When steam is passed over red hot carbon the substances produced are

C. hydrogen and carbon (ii) oxide

A. hydrogen and trioxocarbonate (IV) acid

B. hydrogen, oxygen and carbon (IV) oxide

C. hydrogen and carbon (ii) oxide

D. hydrogen and carbon (IV) oxide

A difference between chemical and physical change is that in a chemical change

C. the reversible process occurs

Rare gases are stable because they

C. have duplet or octet electronic configuration in the outermost shells in their atoms

In the industrial production of H2 from water gas the CO2 produced along with the H2 is removed by

B. drying over phosphorus (V) oxide

C. passing the mixture to the limewater

D. using ammonical copper (I) chlorine

Electronic configuration of an element 13 in the subsidiary energy level is

A. $ 1s^2 2s^2 2p^6 3s^2 3p^1 $

C. $ 1s^2 2s^2 2p^6 3s^2 3p^3 $

D. $ 1s^1 2s^2 2p^6 3s^2 3p^4 $

A suitable reagent for distinguish between ethanoic and ethanol is

C. sodium hydrogen trioxocarbonate (iv)

D. Ammoniacal silver trioxonitrate(V)

In countries where the temperature fall below 273k, salt always spilled on the road in order to

D. reduce the freezing point of ice

B. increase the density of the ice

D. reduce the freezing point of ice

In the production of soap, concentrated sodium chloride solution is added to

B. decrease the solubility of the soap

A. increase the solubility of soap

B. decrease the solubility of the soap

Alloys are best prepared by

D. cooking a molten of the metals

C. reducing and mixture of their metallic

D. cooking a molten of the metals

JAMB 2015

2015 JAMB Chemistry Past Questions

The 2015 JAMB Chemistry past questions with answers: 64 objective questions from the 2015 paper in the DeeepSolve question bank, each with its answer behind "Show answer". Try each question before you check, then practise the paper as a timed JAMB-style CBT.

Practise this paper as a timed JAMB-style CBT All JAMB Chemistry years

Questions

1.
When sugar is dissolve in tea, the reaction is accomplished by?
1. A.positive change
2. B.negative entropy change
3. C.no entropy change
4. D.a minimum entropy change
Show answer
Answer: A. positive change
AI explanation
Analysis
The question asks about the thermodynamic change that occurs when a solid solute (sugar) dissolves in a solvent (tea/water). Specifically, it focuses on the concept of entropy.
Concept Explanation
Entropy ( $S$ ) is a measure of the degree of disorder or randomness in a system.
Solid state: Particles are tightly packed in an orderly arrangement, so entropy is low.
Liquid/Solution state: Particles are free to move and are more randomly distributed, so entropy is higher.
When you dissolve sugar (a solid) into tea (a liquid), the sugar molecules break away from their rigid crystal lattice and disperse throughout the liquid. This transition from a highly ordered solid state to a more disordered, dispersed state in the solution represents an increase in entropy.
In thermodynamics, an increase in entropy is represented as a positive change ( $\Delta S > 0$ ).
Step-by-Step Solution
Identify the system: We are moving from a solid (sugar) to a solution (sugar dissolved in tea).
Analyze the disorder: The sugar molecules move from a fixed, ordered position in the crystal to a random, disordered state in the liquid.
Relate to Entropy: Since the disorder of the system has increased, the change in entropy ( $\Delta S$ ) is positive.
Evaluate the options: • A (positive change): This matches our finding that entropy increases. • B (negative entropy change): This would imply the system became more ordered, which is incorrect for dissolving a solid. • C (no entropy change): This is incorrect because the state of the sugar has clearly changed. • D (a minimum entropy change): This is not the standard thermodynamic description for the dissolution process.
Conclusion
The dissolution of sugar in tea leads to an increase in the randomness of the sugar molecules, which is defined as a positive change in entropy.
Exam Tip: Always remember the "Disorder Rule":
Melting (solid to liquid) = Positive entropy change.
Boiling (liquid to gas) = Positive entropy change.
Dissolving a solid in a liquid = Positive entropy change.
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2.
A small quantity of solid ammonium chloride (NH4Cl) heated gently in a test tube, the solid gradually disappear produce two gases. Later, a white cloudy deposit was absence on the cooler part of the test tube. The ammonium chloride is to have undergo
1. A.distillation
2. B.sublimation
3. C.precipitation
4. D.evaporation
Show answer
Answer: B. sublimation
AI explanation
Analysis of the Question
The question describes a process where a solid substance (ammonium chloride) is heated and changes directly into gases without passing through a liquid state. Upon cooling, these gases recombine to form a solid deposit on the cooler parts of the test tube. We need to identify the specific physical process occurring here.
Concept Explanation
The phenomenon described is sublimation.
Sublimation is the process where a solid changes directly into a gas upon heating, without becoming a liquid first.
When the gas cools down, it undergoes deposition (the reverse of sublimation), turning back into a solid.
Ammonium chloride ( $NH_4Cl$ ) is a classic example of a substance that sublimes. When heated, it dissociates into ammonia ( $NH_3$ ) and hydrogen chloride ( $HCl$ ) gases, which then recombine as they cool to form the white solid deposit.
Step-by-Step Solution
Identify the change of state: The solid disappears (turns to gas) upon heating. This eliminates precipitation (which involves forming a solid from a solution) and evaporation (which involves a liquid turning into a gas).
Evaluate the options: • Distillation: This involves boiling a liquid and condensing the vapor. Since we started with a solid, this is incorrect. • Sublimation: This matches the definition of a solid turning directly into a gas and back to a solid. • Precipitation: This occurs in liquid solutions, not by heating a dry solid. • Evaporation: This is the conversion of a liquid to a gas.
Conclusion: The observation of the solid disappearing and reappearing as a white cloud on the cooler part of the test tube is the textbook definition of sublimation.
Exam Tip
Whenever you see questions involving substances like Ammonium Chloride ( $NH_4Cl$ ), Iodine ( $I_2$ ), Naphthalene (mothballs), or Camphor, immediately think of sublimation. These are the most common substances used in JAMB/WASSCE questions to test this concept.
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3.
Vulcanization involve the removal of
1. A.monometer
2. B.the single bond
3. C.the double bond
4. D.a polymer
Show answer
Answer: C. the double bond
AI explanation
1. Analyze the question
The question asks for the chemical process that occurs during the vulcanization of rubber. Specifically, it asks what is removed or altered in the structure of the rubber polymer during this process.
2. Explain the concept
Vulcanization is a chemical process used to improve the physical properties of natural rubber (polyisoprene). Natural rubber is soft, sticky when hot, and brittle when cold.
Natural rubber consists of long polymer chains of isoprene units. These chains contain carbon-carbon double bonds (C=C). During vulcanization, sulfur is added to the rubber and heated. The sulfur atoms form "cross-links" (bridges) between the polymer chains.
To form these cross-links, the sulfur atoms must attach to the carbon atoms. This reaction involves the breaking of the carbon-carbon double bonds in the polymer chain, which allows the sulfur to bond to the carbon atoms and create a stable, cross-linked network.
3. Show the solution
Step 1: Identify the structure of natural rubber: It is a polymer of isoprene, which contains unsaturated double bonds ( $C=C$ ).
Step 2: Understand the vulcanization reaction: Sulfur is introduced to cross-link the polymer chains.
Step 3: Determine the chemical change: For the sulfur to form a bridge between two chains, the existing double bonds must be broken (saturated) so that the carbon atoms can form new single bonds with the sulfur atoms.
Step 4: Conclusion: The process effectively removes the double bonds by converting them into single bonds as part of the cross-linking process.
4. Identify the answer
The correct option is C. Vulcanization involves the saturation of the double bonds in the polymer chain to create cross-links.
5. Exam Tip
Think of vulcanization as "stitching" together loose threads (polymer chains). To stitch them together, you have to "open up" the existing structure (the double bonds) to make room for the "thread" (the sulfur atoms). Remember: Vulcanization = Sulfur + Heat = Cross-linking = Breaking double bonds.
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4.
Which of the following ions requires the largest quantity of electricity for discharge at an electrode?
1. A.2.0 mole of Q3+
2. B.2.5 mole of R2+
3. C.3.0 mole of T-
4. D.4.0 mole of Y-
Show answer
Answer: A. 2.0 mole of Q3+
AI explanation
Analysis
To determine which ion requires the largest quantity of electricity for discharge, we use Faraday’s First Law of Electrolysis. The quantity of electricity ( $Q$ ) required to discharge an ion is directly proportional to the number of moles of the ion and its valency (charge).
Concept
The formula for the quantity of electricity ( $Q$ ) in terms of Faraday's constant ( $F$ ) is:
$Q = n \times z \times F$
Where:
$n$ = number of moles of the ion
$z$ = charge (valency) of the ion
$F$ = Faraday's constant (approx. 96,500 Coulombs/mole)
Since $F$ is a constant, we only need to calculate the product of moles ( $n$ ) × charge ( $z$ ) for each option to compare the relative quantities of electricity.
Step-by-Step Solution
Let's calculate the value of $n \times z$ for each option:
Option A: 2.0 mole of Q³⁺ • $n = 2.0$ , $z = 3$ • $Q \propto 2.0 \times 3 = \mathbf{6.0}$
Option B: 2.5 mole of R²⁺ • $n = 2.5$ , $z = 2$ • $Q \propto 2.5 \times 2 = \mathbf{5.0}$
Option C: 3.0 mole of T⁻ • $n = 3.0$ , $z = 1$ • $Q \propto 3.0 \times 1 = \mathbf{3.0}$
Option D: 4.0 mole of Y⁻ • $n = 4.0$ , $z = 1$ • $Q \propto 4.0 \times 1 = \mathbf{4.0}$
Comparing the results (6.0, 5.0, 3.0, and 4.0), the highest value is 6.0, which corresponds to Option A.
Conclusion
Option A requires the largest quantity of electricity because it involves the highest product of moles and ionic charge.
Exam Tip
When solving electrolysis problems, remember that the charge of the ion acts as a "multiplier" for the amount of electricity needed. Even if you have a large number of moles, a low-valency ion (like a monovalent ion with charge 1) might still require less electricity than a smaller number of moles of a highly charged ion (like a trivalent ion with charge 3). Always calculate $n \times z$ to be safe!
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5.
When steam is passed over red hot carbon the substances produced are
1. A.hydrogen and trioxocarbonate (IV) acid
2. B.hydrogen, oxygen and carbon (IV) oxide
3. C.hydrogen and carbon (ii) oxide
4. D.hydrogen and carbon (IV) oxide
Show answer
Answer: C. hydrogen and carbon (ii) oxide
AI explanation
Analysis
The question asks for the chemical products formed when steam (water vapor) reacts with red-hot carbon. This is a classic industrial process known as the production of water gas.
Concept
When steam ( $H_2O$ ) is passed over red-hot carbon (coke) at a high temperature (approximately 1000°C), a redox reaction occurs. The carbon acts as a reducing agent, removing oxygen from the water molecule.
The chemical equation for this reaction is: $C(s) + H_2O(g) \rightarrow CO(g) + H_2(g)$
$C$ : Carbon (red-hot coke)
$H_2O$ : Steam
$CO$ : Carbon(II) oxide (also known as carbon monoxide)
$H_2$ : Hydrogen gas
The mixture of carbon(II) oxide and hydrogen is collectively called water gas, which is an important industrial fuel.
Step-by-Step Solution
Identify the reactants: Carbon ( $C$ ) and Steam ( $H_2O$ ).
Determine the reaction type: This is a displacement reaction where carbon reduces steam.
Balance the equation: • One atom of Carbon on the left, one on the right. • Two atoms of Hydrogen on the left, two on the right. • One atom of Oxygen on the left, one on the right. • The equation $C + H_2O \rightarrow CO + H_2$ is balanced.
Identify the products: The products are Carbon(II) oxide ( $CO$ ) and Hydrogen gas ( $H_2$ ).
Comparing this to your options:
Option A mentions trioxocarbonate(IV) acid (carbonic acid), which is incorrect.
Option B mentions oxygen, which is not produced.
Option C matches our derived products: hydrogen and carbon(II) oxide.
Option D mentions carbon(IV) oxide ( $CO_2$ ), which is only produced if the reaction occurs at a lower temperature or with excess steam, but the standard reaction for "red hot carbon" is the production of water gas.
Exam Tip
Remember the term "Water Gas". Whenever you see "steam + red hot carbon," immediately think of the mixture $CO + H_2$ . If the question had said "excess steam," then carbon(IV) oxide ( $CO_2$ ) would be produced instead of carbon(II) oxide, but for standard red-hot carbon, stick with $CO$ .
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6.
Which of the following metals burns with brick red
1. A.Pb
2. B.Ca
3. C.Na
4. D.Mg
Show answer
Answer: B. Ca
AI explanation
Analysis
The question asks for the identification of a metal based on the characteristic color it produces when burned in a flame. This is a classic test used in qualitative analysis known as the Flame Test.
Concept: Flame Test
The flame test is used to identify the presence of certain metal ions in a compound. When these metals are heated in a Bunsen burner flame, the electrons in the metal atoms absorb energy and jump to higher energy levels. As they return to their ground state, they emit light at specific wavelengths, which appear as distinct colors.
Sodium (Na): Produces a persistent golden-yellow flame.
Calcium (Ca): Produces a brick-red flame.
Lead (Pb): Does not produce a characteristic flame color (it is often associated with a greyish-white smoke).
Magnesium (Mg): Produces a brilliant white light (often used in flares).
Step-by-Step Solution
Evaluate the options: We need to match each metal to its flame color.
Analyze Option A (Pb): Lead does not give a distinct flame color.
Analyze Option B (Ca): Calcium ions ( $Ca^{2+}$ ) are well-documented in chemistry to impart a "brick-red" or "orange-red" color to a non-luminous Bunsen flame.
Analyze Option C (Na): Sodium is famous for its bright yellow flame.
Analyze Option D (Mg): Magnesium burns with a blinding white light, not red.
Conclusion: Based on the standard flame test results, Calcium is the correct metal.
Exam Tip
To remember these colors for your JAMB/WASSCE exams, use this simple mnemonic:
Sodium = Sunshine (Yellow)
Calcium = Carrot (Brick-red/Orange)
K (Potassium) = Krimson/Lilac
Barium = Baby green (Apple green)
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7.
According to the kinetic theory an absence in temperature causes the kinetic energy of particles to
1. A.decrease
2. B.increase
3. C.remain constant
4. D.be zero
Show answer
Answer: B. increase
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8.
Flow of current in electrolytes is due to the movement of
1. A.electrons
2. B.Holes and electron
3. C.Ions
4. D.Charges
Show answer
Answer: C. Ions
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9.
Which of these radioactive elements is commonly used as a nuclear fuel
1. A.uranium
2. B.palladium
3. C.actium
4. D.thorium
Show answer
Answer: A. uranium
AI explanation
Analysis
The question asks for a radioactive element that is widely utilized as a fuel source in nuclear power plants to generate electricity through the process of nuclear fission.
Concept Explanation
Nuclear fuel is a substance that can be consumed by nuclear reactors to release energy. The most common process used is nuclear fission, where the nucleus of a heavy atom is split into smaller nuclei, releasing a massive amount of energy in the form of heat.
For an element to be an effective nuclear fuel, it must be fissile (capable of sustaining a chain reaction). Uranium-235 is the most widely used isotope for this purpose because its nucleus is unstable enough to be split by neutrons, yet stable enough to be handled and processed into fuel rods.
Step-by-Step Solution
Evaluate Option A (Uranium): Uranium (specifically the isotope U-235) is the primary fuel used in nuclear reactors worldwide. When bombarded with neutrons, it undergoes fission, releasing energy and more neutrons to sustain the reaction.
Evaluate Option B (Palladium): Palladium is a transition metal used primarily in catalytic converters and electronics. It is not a radioactive fuel source.
Evaluate Option C (Actinium): Actinium is a rare radioactive element. While it is radioactive, it is not used as a nuclear fuel due to its scarcity and high cost of production.
Evaluate Option D (Thorium): While Thorium is being researched as a potential future nuclear fuel (it is "fertile" rather than "fissile"), it is not currently the standard, commonly used nuclear fuel compared to Uranium.
Conclusion
Based on standard nuclear physics and industrial applications, Uranium is the element universally recognized as the primary nuclear fuel.
Exam Tip
When you see questions about "nuclear fuel" in JAMB Chemistry, always look for Uranium or Plutonium. These are the two heavy elements that dominate the nuclear energy industry. Don't get distracted by other radioactive elements like Thorium or Actinium, which are either experimental or not used for power generation.
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10.
The weakest attractive force that can be observed between two molecules is
1. A.ionic
2. B.covalent
3. C.co-ordinate covalent
4. D.vander Waals
Show answer
Answer: D. vander Waals
AI explanation
Analysis
The question asks us to identify the weakest type of attractive force among the options provided. To answer this, we must compare the relative strengths of chemical bonds and intermolecular forces.
Concept Explanation
In chemistry, forces of attraction are generally categorized into two groups:
Intramolecular forces (Chemical Bonds): These are the forces that hold atoms together within a molecule. They are very strong. Examples include: • Ionic bonds: Electrostatic attraction between oppositely charged ions. • Covalent bonds: Sharing of electron pairs between atoms. • Co-ordinate covalent (Dative) bonds: A type of covalent bond where both electrons come from one atom.
Intermolecular forces: These are the forces of attraction between separate molecules. They are significantly weaker than chemical bonds. Van der Waals forces are the weakest of these intermolecular forces. They arise from temporary fluctuations in electron distribution, creating temporary dipoles.
Step-by-Step Solution
Evaluate Options A, B, and C: Ionic, Covalent, and Co-ordinate covalent bonds are all strong chemical bonds. They require a significant amount of energy to break because they involve the transfer or sharing of electrons to achieve stable electronic configurations.
Evaluate Option D: Van der Waals forces are weak, short-range electrostatic attractions between molecules. Because they depend on temporary or induced dipoles, they are easily disrupted by thermal energy.
Comparison: Since Van der Waals forces are intermolecular and the others are intramolecular, Van der Waals forces are significantly weaker than the bonds listed in A, B, and C.
Conclusion
The weakest attractive force among the choices is the Van der Waals force.
Exam Tip
Remember the hierarchy of strength: Ionic > Covalent > Hydrogen Bonding > Van der Waals. If you ever forget, think about the state of matter: substances held together by Van der Waals forces (like noble gases or non-polar molecules) usually have very low melting and boiling points because the forces are so easy to overcome!
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11.
A difference between chemical and physical change is that in a chemical change
1. A.oxygen is consumed
2. B.heat is supplied
3. C.the reversible process occurs
4. D.a new substance is formed
Show answer
Answer: D. a new substance is formed
AI explanation
1. Analyze the question
The question asks for the fundamental distinction between a physical change and a chemical change. You need to identify which of the provided options is a unique characteristic of chemical changes that does not apply to physical changes.
2. Explain the concept
Physical Change: This is a change in the state or appearance of matter without changing its chemical composition. No new substance is created. Examples include melting ice (solid to liquid), dissolving sugar in water, or tearing paper. These processes are often easily reversible.
Chemical Change: This involves a chemical reaction where the original substances (reactants) are transformed into entirely new substances (products) with different chemical properties. This process is usually permanent and difficult to reverse. Examples include rusting of iron, burning wood, or the souring of milk.
3. Show the solution
Let’s evaluate the options:
A (Oxygen is consumed): While oxygen is consumed in combustion (a chemical change), it is not consumed in all chemical changes (e.g., the decomposition of calcium carbonate).
B (Heat is supplied): Heat can be supplied in both physical changes (like boiling water) and chemical changes (like thermal decomposition). Therefore, this is not a defining difference.
C (The reversible process occurs): Physical changes are typically reversible, but some chemical changes are also reversible (e.g., the Haber process). This is not the primary distinction.
D (A new substance is formed): This is the hallmark of a chemical change. In a chemical reaction, atoms are rearranged to form new chemical bonds, resulting in a product that is chemically different from the starting material. This never happens in a physical change.
4. Identify the answer
A chemical change is defined by the formation of a new substance, whereas a physical change only alters the form or state of the existing substance.
5. Tip
Memory Trick: Think of the "New Substance" rule. If you can't easily "undo" the change to get your original material back (like trying to turn ash back into wood), it is almost certainly a chemical change because a new substance has been formed!
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12.
Which of the following gives a precipitation when treated with NaOH Solution?
1. A.AlCl3
2. B.NH4Cl
3. C.Na2CO3
4. D.CH3COONa
Show answer
Answer: A. AlCl3
AI explanation
Analysis
The question asks us to identify which of the given substances will form a precipitate when reacted with Sodium Hydroxide (NaOH) solution. In chemistry, a precipitate is an insoluble solid that emerges from a liquid solution.
Concept
When NaOH is added to a solution, it provides hydroxide ions ( $OH^-$ ). If these ions react with a metal cation to form an insoluble metal hydroxide, a precipitate will be observed.
Aluminium ions ( $Al^{3+}$ ) react with $OH^-$ to form Aluminium hydroxide, $Al(OH)_3$ , which is a white gelatinous precipitate.
Ammonium ions ( $NH_4^+$ ) react with $OH^-$ to produce ammonia gas ( $NH_3$ ) and water, not a precipitate.
Sodium ions ( $Na^+$ ) and Carbonate ions ( $CO_3^{2-}$ ) are generally soluble in water, so they do not form precipitates with NaOH.
Step-by-Step Solution
Evaluate Option A ( $AlCl_3$ ): When $AlCl_3$ reacts with $NaOH$ , the following reaction occurs: $AlCl_3(aq) + 3NaOH(aq) \rightarrow Al(OH)_3(s) + 3NaCl(aq)$ $Al(OH)_3$ is an insoluble white precipitate. This fits the criteria.
Evaluate Option B ( $NH_4Cl$ ): $NH_4Cl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_2O(l) + NH_3(g)$ This reaction produces ammonia gas (which has a pungent smell), but no precipitate is formed.
Evaluate Option C ( $Na_2CO_3$ ): $Na_2CO_3$ is a sodium salt. Sodium salts are highly soluble in water. Adding $NaOH$ (which also contains sodium) will not result in any reaction or precipitation.
Evaluate Option D ( $CH_3COONa$ ): This is Sodium ethanoate. Like $Na_2CO_3$ , it is a soluble salt and will not form a precipitate when more sodium ions and hydroxide ions are added.
Conclusion
Only $AlCl_3$ produces an insoluble hydroxide precipitate upon the addition of $NaOH$ .
Exam Tip
Remember the "Solubility Rules": Most metal hydroxides are insoluble in water (except for Group 1 metals like $Na^+$ and $K^+$ ). Since $Al^{3+}$ is not a Group 1 metal, its hydroxide is insoluble and will form a precipitate.
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13.
All these are electromagnetic waves except
1. A.White light
2. B.Photon
3. C.X-ray
4. D.Infrared
Show answer
Answer: B. Photon
AI explanation
Analysis
The question asks us to identify which of the listed items is not an electromagnetic wave. To answer this, we must understand what constitutes the electromagnetic spectrum.
Concept Explanation
Electromagnetic (EM) waves are waves that are created as a result of vibrations between an electric field and a magnetic field. They do not require a medium to travel (they can travel through a vacuum). The electromagnetic spectrum includes:
Radio waves
Microwaves
Infrared radiation
Visible light (White light)
Ultraviolet rays
X-rays
Gamma rays
A photon, on the other hand, is not a wave itself; it is a quantum or a "packet" of electromagnetic energy. While electromagnetic waves exhibit particle-like behavior (the wave-particle duality), a photon is defined as the fundamental particle of light, not the wave itself.
Step-by-Step Solution
Evaluate Option A (White light): White light is part of the visible spectrum of electromagnetic waves.
Evaluate Option B (Photon): A photon is a discrete particle of electromagnetic radiation. It is the carrier of the electromagnetic force, but it is classified as a subatomic particle, not a wave.
Evaluate Option C (X-ray): X-rays are high-energy electromagnetic waves used in medical imaging.
Evaluate Option D (Infrared): Infrared radiation is a type of electromagnetic wave with a wavelength longer than visible light.
Comparing these, while all the others represent types or ranges of electromagnetic waves, a photon is the particle unit of that energy. Therefore, it is the odd one out.
Conclusion
Exam Tip
When you see questions about the electromagnetic spectrum, remember the mnemonic: "Raging Martians Invaded Venus Using X-ray Guns" (Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma). If an option isn't on that list, it's likely the answer!
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14.
The substance that is used in the steel industry for the removal of carbon. Sulphur and phosphorus impurities from pig iron is
1. A.oxygen
2. B.chlorine
3. C.nitrogen
4. D.hydrogen
Show answer
Answer: A. oxygen
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15.
In the electrolysis of brine the anode is
1. A.platinum
2. B.copper
3. C.zinc
4. D.carbon
Show answer
Answer: D. carbon
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16.
When salt loses its water of crystallization to the atmosphere on exposure, the process is said to be
1. A.efflorescence
2. B.déliquescence
3. C.effervescence
4. D.fluorescence
Show answer
Answer: A. efflorescence
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17.
The principal constituent of natural gas is
1. A.methane
2. B.ethane
3. C.propane
4. D.Butane
Show answer
Answer: A. methane
AI explanation
Analysis
The question asks for the primary chemical component found in natural gas. Natural gas is a fossil fuel energy source that consists mostly of simple hydrocarbons.
Concept
Natural gas is primarily composed of alkanes, which are saturated hydrocarbons. While natural gas can contain small amounts of ethane, propane, and butane, the vast majority (often 70% to 90%) of its composition is the simplest alkane, which has the chemical formula $CH_4$ .
Solution
Identify the components: Natural gas is a mixture of gaseous hydrocarbons.
Evaluate the options: • Methane ( $CH_4$ ): This is the simplest hydrocarbon and the most abundant component in natural gas deposits. • Ethane ( $C_2H_6$ ): Present in smaller quantities. • Propane ( $C_3H_8$ ) and Butane ( $C_4H_{10}$ ): These are often separated from natural gas to be sold as Liquefied Petroleum Gas (LPG) for cooking and heating.
Conclusion: Since methane makes up the largest percentage of natural gas, it is considered its principal constituent.
Correct Answer
The correct option is A.
Exam Tip
To remember this easily, think of the acronym "MEP-B" for the first four alkanes (Methane, Ethane, Propane, Butane). Always remember that Methane is the "king" of natural gas, while Butane/Propane are the main components of the gas cylinders we use in our kitchens (LPG).
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18.
PCL5(g)= PCL3(g) + Cl2(g) In the reaction above, a decrease in pressure will
1. A.Decelerate the reaction
2. B.Increase yield of Pcl3
3. C.Increase the yield of Pcl5
4. D.Accurate the reaction
Show answer
Answer: B. Increase yield of Pcl3
AI explanation
Analysis
This question tests your understanding of Le Chatelier’s Principle, which states that if a dynamic equilibrium is disturbed by changing the conditions (such as pressure, temperature, or concentration), the position of equilibrium shifts to counteract the change.
Concept: Effect of Pressure on Equilibrium
To determine how pressure affects a gaseous equilibrium, look at the number of moles of gas on both sides of the equation:
Reactant side: $PCl_5(g)$ = 1 mole of gas.
Product side: $PCl_3(g) + Cl_2(g)$ = 1 + 1 = 2 moles of gas.
The Rule:
Increase in pressure: The equilibrium shifts toward the side with fewer moles of gas to reduce the pressure.
Decrease in pressure: The equilibrium shifts toward the side with more moles of gas to increase the pressure.
Step-by-Step Solution
Identify the change: The question specifies a decrease in pressure.
Apply the rule: According to Le Chatelier’s Principle, a decrease in pressure favors the side with a larger volume (more moles of gas).
Analyze the reaction: • The product side has 2 moles of gas. • The reactant side has 1 mole of gas.
Determine the shift: Since the product side has more moles, a decrease in pressure will shift the equilibrium to the right (towards the products).
Conclusion: Shifting to the right means more $PCl_5$ is consumed to produce more $PCl_3$ and $Cl_2$ . Therefore, the yield of $PCl_3$ increases.
Evaluation of Options
A & D: Pressure changes affect the position of equilibrium, not necessarily the rate (deceleration/acceleration) in the context of equilibrium yield.
C: This would happen if pressure were increased.
B: This is correct because the equilibrium shifts to the side with more moles (the products).
*
Exam Tip
Always count the moles of gas on both sides of the equation before applying pressure rules. Remember: "High pressure favors the side with fewer moles; Low pressure favors the side with more moles."
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19.
If glucose is heated with concentrated tetraoxosulphate(vi)acid, it will be dehydrated to?
1. A.carbon
2. B.carbon(iv)oxide
3. C.ethane
4. D.ethanol
Show answer
Answer: A. carbon
AI explanation
Analysis
The question asks for the product formed when glucose ( $C_6H_{12}O_6$ ) undergoes a dehydration reaction in the presence of concentrated tetraoxosulphate(VI) acid ( $H_2SO_4$ ).
Concept Explanation
Concentrated tetraoxosulphate(VI) acid is a powerful dehydrating agent. In chemistry, dehydration refers to the removal of water molecules ( $H_2O$ ) from a compound.
Glucose is a carbohydrate, which literally means "hydrated carbon" ( $C_n(H_2O)_m$ ). When concentrated $H_2SO_4$ is added to glucose, it strips away the hydrogen and oxygen atoms in the ratio of 2:1 (the ratio found in water), leaving behind the carbon atoms.
Step-by-Step Solution
Identify the chemical formula of glucose: $C_6H_{12}O_6$ .
Understand the role of the reagent: Concentrated $H_2SO_4$ acts as a dehydrating agent, meaning it removes water ( $H_2O$ ) from the molecule.
Write the chemical equation: $ $C_6H_{12}O_6 \xrightarrow{\text{conc. } H_2SO_4} 6C + 6H_2O$ $
Observe the products: The glucose molecule is broken down into 6 atoms of carbon (a black, porous solid) and 6 molecules of water.
Conclusion
Because the acid removes all the hydrogen and oxygen as water, only the carbon remains. Therefore, glucose is dehydrated to carbon.
Exam Tip
Whenever you see "concentrated tetraoxosulphate(VI) acid" acting on carbohydrates like sugar or glucose, always associate it with the production of carbon (which appears as a black charred mass). This is a classic dehydration reaction frequently tested in JAMB.
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20.
The energy value of petrol can be determined by
1. A.Bomb calorimeter
2. B.Catalytic cracker
3. C.Fractionating column
4. D.Thermometer
Show answer
Answer: A. Bomb calorimeter
AI explanation
Analysis
The question asks for the specific laboratory apparatus used to measure the energy content (heat of combustion) of a fuel like petrol.
Concept Explanation
In chemistry, the heat of combustion is the amount of heat energy released when a specific amount of a substance is burned completely in oxygen. To measure this accurately, we use a device called a calorimeter.
Specifically, for fuels like petrol, which are volatile and release a large amount of energy, we use a Bomb calorimeter.
How it works: A known mass of the fuel is placed in a sealed, strong steel container (the "bomb") filled with pure oxygen. This bomb is submerged in a known volume of water. The fuel is ignited electrically, and the heat released is absorbed by the water. By measuring the temperature change of the water, we can calculate the energy value of the fuel using the formula: $q = mc\Delta T$ .
Step-by-Step Solution
Evaluate Option A (Bomb calorimeter): This is a constant-volume calorimeter used specifically to measure the heat of combustion of substances. It is the standard tool for determining the energy value of fuels.
Evaluate Option B (Catalytic cracker): This is an industrial unit used in petroleum refineries to break down heavy hydrocarbons into lighter, more valuable products like petrol. It is not a measuring instrument.
Evaluate Option C (Fractionating column): This is used in the process of fractional distillation to separate crude oil into different components based on their boiling points. It does not measure energy.
Evaluate Option D (Thermometer): While a thermometer is a part of a calorimeter used to measure temperature change, it is not the complete apparatus used to determine the energy value of a fuel on its own.
Conclusion
The Bomb calorimeter is the correct apparatus designed for this purpose.
Exam Tip: Whenever you see questions about "heat of combustion" or "energy value" of fuels in your JAMB or WASSCE exams, always look for "calorimeter." If the fuel is a solid or liquid, "Bomb calorimeter" is the specific type you need to identify.
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21.
The filter in the cigarette reduce the nicotine construct by
1. A.burning
2. B.adsorption
3. C.evaporation
4. D.absorption
Show answer
Answer: B. adsorption
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22.
P1V1 = P2V2 supports ?
1. A.Charles’s law
2. B.Boyles’s law
3. C.Graham’s law
4. D.Avogadro’s law
Show answer
Answer: B. Boyles’s law
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23.
NH3(g) + HCl(s) → NH 4Cl (s) The entropy change in the system above is
1. A.positive
2. B.zero
3. C.negative
4. D.intermediate
Show answer
Answer: C. negative
AI explanation
Analysis of the Question
The question asks for the sign of the entropy change ( $\Delta S$ ) for the reaction:
$\text{NH}_3(g) + \text{HCl}(g) \rightarrow \text{NH}_4\text{Cl}(s)$
(Note: While the question lists HCl as a solid, the reaction between ammonia and hydrogen chloride gas is a classic example of a gas-phase reaction forming a solid.)
Concept Explanation
Entropy ( $S$ ) is a measure of the degree of disorder or randomness in a system.
Gases have the highest entropy because their particles move randomly and occupy a large volume.
Liquids have intermediate entropy.
Solids have the lowest entropy because their particles are fixed in a rigid, ordered lattice structure.
The entropy change ( $\Delta S$ ) is calculated as:
$\Delta S = S_{\text{products}} - S_{\text{reactants}}$
If the system moves from a state of high disorder (gases) to a state of high order (solid), the entropy decreases, meaning $\Delta S$ is negative.
Step-by-Step Solution
Examine the reactants: We have two moles of gaseous substances ( $\text{NH}_3$ and $\text{HCl}$ ). Gases have high entropy.
Examine the product: We have one mole of a solid substance ( $\text{NH}_4\text{Cl}$ ). Solids have very low entropy.
Compare: The reaction involves the conversion of highly disordered gaseous molecules into a highly ordered solid crystal lattice.
Conclusion: Since the system is becoming more ordered (moving from gas to solid), the final entropy is lower than the initial entropy. Therefore, $\Delta S$ must be negative.
Identification of the Answer
The correct option is C.
Exam Tip
Whenever you see a reaction where the number of moles of gas decreases (or gas is converted to solid/liquid), the entropy change is almost always negative. Conversely, if a solid decomposes into gases, the entropy change is positive.
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24.
Rare gases are stable because they
1. A.are monoatomic
2. B.form ions easily
3. C.have duplet or octet electronic configuration in the outermost shells in their atoms
4. D.are volatile gases
Show answer
Answer: C. have duplet or octet electronic configuration in the outermost shells in their atoms
AI explanation
Analysis
The question asks for the fundamental reason behind the chemical stability (or inertness) of rare gases (also known as noble gases or Group 18 elements).
Concept Explanation
In chemistry, the stability of an atom is largely determined by its electronic configuration. Atoms generally react with one another to achieve a stable state, which is defined by having a "full" outermost shell.
The Octet Rule: Most elements strive to have 8 electrons in their outermost shell (an octet) to achieve stability, similar to the noble gases.
The Duplet Rule: For the smallest element, Helium (He), stability is achieved with 2 electrons in its outermost shell (a duplet).
Noble Gases: Elements like Helium, Neon, Argon, Krypton, Xenon, and Radon already possess these full outer shells naturally. Because their outermost shells are completely filled, they have no tendency to gain, lose, or share electrons. This makes them chemically inert or "stable."
Step-by-Step Solution
Evaluate Option A: While it is true that rare gases are monoatomic, being monoatomic is a result of their stability, not the cause of it.
Evaluate Option B: Rare gases do not form ions easily. In fact, they are known for their extremely high ionization energies, meaning they resist losing electrons.
Evaluate Option C: This describes the electronic structure of the noble gases. Because they have a full duplet (for Helium) or a full octet (for the others), they have no "vacancies" in their valence shells. This lack of vacancy prevents them from reacting with other elements under normal conditions.
Evaluate Option D: Being volatile is a physical property related to boiling points and intermolecular forces, but it does not explain why they are chemically stable.
Conclusion
The stability of rare gases is a direct consequence of their electronic configuration. Having a full outer shell (duplet or octet) means they have reached the lowest possible energy state, making them unreactive.
Exam Tip: Whenever you see a question about the reactivity of elements, always look for the option that mentions the "outermost shell" or "valence electrons." Elements react specifically to complete their octet; if they already have it, they stay stable!
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25.
Hydrogen can be displaced from a hot alkaline solution by
1. A.Fe
2. B.Cu
3. C.Ca
4. D.Sn
Show answer
Answer: D. Sn
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26.
The elements that belong to the third period of periodic table are
1. A.Li, Be, Al and D
2. B.Na, P, O and Cl
3. C.B, C, N, and O
4. D.Na, Mg, S and Ar
Show answer
Answer: D. Na, Mg, S and Ar
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27.
Which of these require crystallization most?
1. A.Drug making
2. B.Cement making
3. C.Paint making
4. D.Perfume making
Show answer
Answer: A. Drug making
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28.
In the electrolysis of CuSo4(g) using platinum electrode the reaction at the anode is
1. A.4H+ 4e - 2H2
2. B.4OH= 4e- + 2H2O + O2
3. C.2OH - 2e- = 2OH
4. D.2OH- + 2OH = 2H2O + O2
Show answer
Answer: B. 4OH= 4e- + 2H2O + O2
AI explanation
Analysis of the Question
The question asks for the reaction occurring at the anode during the electrolysis of aqueous copper(II) tetraoxosulphate(VI) solution ( $\text{CuSO}_4$ ) using platinum (inert) electrodes.
Concept Explanation
In the electrolysis of an aqueous solution, we must consider the ions present in the electrolyte and the nature of the electrodes:
Ions present: $\text{Cu}^{2+}$ and $\text{SO}_4^{2-}$ from the salt, and $\text{H}^+$ and $\text{OH}^-$ from the water.
The Anode (Positive Electrode): Anions ( $\text{SO}_4^{2-}$ and $\text{OH}^-$ ) migrate to the anode. According to the electrochemical series, the hydroxide ion ( $\text{OH}^-$ ) is preferentially discharged over the sulphate ion ( $\text{SO}_4^{2-}$ ).
The Reaction: When $\text{OH}^-$ ions reach the anode, they lose electrons (oxidation) to form water and oxygen gas.
The balanced half-equation for the discharge of hydroxide ions is:
$4\text{OH}^-_{(aq)} \rightarrow 2\text{H}_2\text{O}_{(l)} + \text{O}_{2(g)} + 4e^-$
Rearranging this to show the loss of electrons (as requested in your options):
$4\text{OH}^- - 4e^- \rightarrow 2\text{H}_2\text{O} + \text{O}_2$
Or, moving the electrons to the other side:
$4\text{OH}^- \rightarrow 2\text{H}_2\text{O} + \text{O}_2 + 4e^-$
Step-by-Step Solution
Step 1: Identify the anions migrating to the anode: $\text{SO}_4^{2-}$ and $\text{OH}^-$ .
Step 2: Apply the preferential discharge rule. $\text{OH}^-$ is discharged more easily than $\text{SO}_4^{2-}$ .
Step 3: Write the oxidation half-equation for $\text{OH}^-$ . The hydroxide ion loses an electron to become a neutral hydroxyl radical, which then combines to form water and oxygen gas.
Step 4: Balance the equation. To produce one molecule of $\text{O}_2$ , we need four $\text{OH}^-$ ions, which release four electrons.
Step 5: Compare with the provided options. Option B represents the discharge of hydroxide ions correctly: $4\text{OH}^- \rightarrow 2\text{H}_2\text{O} + \text{O}_2 + 4e^-$ . (Note: The notation in the option $4\text{OH}^- = 4e^- + 2\text{H}_2\text{O} + \text{O}_2$ is a standard way of expressing this in exam formats).
Conclusion
The correct reaction at the anode is the oxidation of hydroxide ions to produce oxygen gas and water.
Correct Option: B
Exam Tip
Remember the mnemonic "OH- Anode": In aqueous electrolysis, if the anion is not a halide (like $\text{Cl}^-$ , $\text{Br}^-$ , or $\text{I}^-$ ), the hydroxide ion ( $\text{OH}^-$ ) from water will almost always be the one discharged at the anode, resulting in the evolution of Oxygen gas.
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29.
Tartaric acid is used industrially to
1. A.make baking powder
2. B.make fruit juice
3. C.remove rust
4. D.dry substance
Show answer
Answer: A. make baking powder
AI explanation
Analysis
The question asks for the industrial application of tartaric acid. To answer this, we need to look at the chemical properties of tartaric acid and its common uses in the food and chemical industries.
Concept Explanation
Tartaric acid ( $C_4H_6O_6$ ) is a naturally occurring organic acid found in many fruits, particularly grapes. In industrial chemistry and food science, it is classified as a weak acid. Its most significant property in this context is its ability to react with bases (like sodium bicarbonate) to release carbon dioxide gas.
Baking Powder: Baking powder is a mixture of a dry acid (often tartaric acid or its salts like cream of tartar) and a base (sodium bicarbonate). When water is added, the acid reacts with the base to produce carbon dioxide gas, which causes dough or batter to rise.
Other options: While tartaric acid is found in some fruits, it is not the primary ingredient used to make fruit juice. It is also not the standard industrial chemical for removing rust (which usually requires stronger acids like hydrochloric or phosphoric acid) or for drying substances (which requires desiccants like silica gel or calcium chloride).
Step-by-Step Solution
Identify the chemical nature: Tartaric acid is an acidic salt used as a leavening agent.
Evaluate the options: • A (Make baking powder): This is a classic application. The reaction between tartaric acid and sodium bicarbonate ( $NaHCO_3$ ) is the fundamental chemistry behind the leavening process in baking. • B (Make fruit juice): Tartaric acid is a component of some fruits, but it is not used to manufacture juice. • C (Remove rust): Rust removal requires stronger mineral acids. • D (Dry substance): Tartaric acid is not a desiccant.
Conclusion: The industrial use of tartaric acid is primarily in the food industry for the production of baking powder.
Correct Option
The correct option is A.
Exam Tip
When you see questions about organic acids in chemistry exams, always associate them with their functional uses:
Citric acid: Used as a preservative and flavoring in drinks.
Tartaric acid: Used in baking powder (leavening).
Ethanoic acid (Acetic acid): Used as vinegar and in the production of esters.
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30.
S block elements of the periodic table one made up of
1. A.groups 1, 2, 3
2. B.groups 1, and 2
3. C.group 3
4. D.group 3 to 7
Show answer
Answer: B. groups 1, and 2
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31.
In the industrial production of H2 from water gas the CO2 produced along with the H2 is removed by
1. A.washing under pressure
2. B.drying over phosphorus (V) oxide
3. C.passing the mixture to the limewater
4. D.using ammonical copper (I) chlorine
Show answer
Answer: A. washing under pressure
AI explanation
Analysis of the Question
The question asks for the industrial method used to remove carbon(IV) oxide ( $CO_2$ ) from a mixture of hydrogen ( $H_2$ ) and $CO_2$ (often called "water gas shift" products).
Concept Explanation
In the industrial production of hydrogen (the Bosch process), water gas ( $CO + H_2$ ) is reacted with steam to produce more hydrogen and carbon(IV) oxide:
$CO(g) + H_2O(g) \rightarrow CO_2(g) + H_2(g)$
To obtain pure hydrogen, the $CO_2$ must be separated from the mixture. Industrially, this is achieved by taking advantage of the solubility of $CO_2$ in water. When the gas mixture is subjected to high pressure, $CO_2$ dissolves readily in water, while hydrogen remains as a gas.
Step-by-Step Solution
Analyze the options: • Option B: Phosphorus(V) oxide is a drying agent used to remove water vapor, not $CO_2$ . • Option C: Limewater ( $Ca(OH)_2$ ) reacts with $CO_2$ to form a precipitate, but this is a laboratory test for $CO_2$ , not an efficient industrial-scale removal method for large volumes of gas. • Option D: Ammoniacal copper(I) chloride is used specifically to remove carbon(II) oxide ( $CO$ ), not $CO_2$ . • Option A: Washing under pressure is the standard industrial technique. By scrubbing the gas mixture with water under high pressure, $CO_2$ is dissolved and washed away, leaving the hydrogen gas behind.
Conclusion: The industrial process relies on the physical solubility of $CO_2$ in water, which is significantly enhanced under high pressure.
Final Answer
The correct option is A.
Exam Tip
When dealing with industrial gas purification questions:
$CO_2$ removal: Think of "washing under pressure" or using alkaline solutions like potassium hydroxide ( $KOH$ ).
$CO$ removal: Think of "ammoniacal copper(I) chloride."
Drying: Think of "concentrated $H_2SO_4$ " or "phosphorus(V) oxide."
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32.
$Cu_2S_{(s)}+ O_{2(g)} = 2CU_{(s)} + SO_{2(g)}$ . In the above reaction, the oxidation number of Cu changes from ___ to _______?
1. A.+1 to 0
2. B.0 to +2
3. C.+2 to +1
4. D.0 to +1
Show answer
Answer: A. +1 to 0
AI explanation
Analysis
To determine the change in the oxidation number of Copper (Cu), we need to calculate the oxidation state of Cu in the reactant ( $Cu_2S$ ) and compare it to its oxidation state in the product ( $Cu$ ).
Concept: Rules for Oxidation Numbers
Elements in their free state: The oxidation number of an atom in its elemental form (like solid Copper, $Cu$ ) is always 0.
Compounds: The sum of oxidation numbers in a neutral compound is 0.
Sulfur: In metal sulfides, Sulfur typically has an oxidation number of -2.
Step-by-Step Solution
Step 1: Find the oxidation number of Cu in $Cu_2S$
Let the oxidation number of Cu be $x$ .
There are two Cu atoms, so we have $2x$ .
The oxidation number of Sulfur (S) is $-2$ .
Since $Cu_2S$ is a neutral compound, the sum is zero: $2x + (-2) = 0$ $2x = 2$ $x = +1$
Therefore, the oxidation number of Cu in $Cu_2S$ is +1.
Step 2: Find the oxidation number of Cu in the product
The product is $Cu_{(s)}$ .
According to the rules, any element in its standard elemental state has an oxidation number of 0.
Step 3: Determine the change
The oxidation number changes from +1 (in $Cu_2S$ ) to 0 (in $Cu$ ).
Conclusion
The oxidation number of Copper decreases from +1 to 0. This indicates that the copper ion is being reduced. Comparing this to your options, it matches option A.
Exam Tip: Always remember that metals in compounds are usually positive, but when they stand alone as a solid element (like $Cu$ , $Fe$ , or $Zn$ ), their oxidation number is always zero. This is a common trap in JAMB Chemistry questions!
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33.
Electronic configuration of an element 13 in the subsidiary energy level is
1. A. $1s^2 2s^2 2p^6 3s^2 3p^1$
2. B. $1s^22s^2 2p^4 3p^1 3s^1$
3. C. $1s^2 2s^2 2p^6 3s^2 3p^3$
4. D. $1s^1 2s^2 2p^6 3s^2 3p^4$
Show answer
Answer: A. $1s^2 2s^2 2p^6 3s^2 3p^1$
AI explanation
Analysis
The question asks for the electronic configuration of an element with an atomic number ( $Z$ ) of 13. In chemistry, the atomic number represents the total number of protons (and electrons in a neutral atom). Therefore, we need to distribute 13 electrons into the various energy levels and subshells following the Aufbau principle.
Concept: The Aufbau Principle
The Aufbau principle states that electrons fill atomic orbitals in order of increasing energy levels. The order of filling is: $1s \rightarrow 2s \rightarrow 2p \rightarrow 3s \rightarrow 3p \rightarrow 4s \dots$
s-orbitals can hold a maximum of 2 electrons.
p-orbitals can hold a maximum of 6 electrons.
Step-by-Step Solution
To find the configuration for $Z = 13$ , we fill the orbitals until we reach a total of 13 electrons:
1s orbital: Holds 2 electrons ( $1s^2$ ). Remaining: $13 - 2 = 11$ .
2s orbital: Holds 2 electrons ( $2s^2$ ). Remaining: $11 - 2 = 9$ .
2p orbital: Holds 6 electrons ( $2p^6$ ). Remaining: $9 - 6 = 3$ .
3s orbital: Holds 2 electrons ( $3s^2$ ). Remaining: $3 - 2 = 1$ .
3p orbital: Holds the final 1 electron ( $3p^1$ ).
Putting it all together, we get: $1s^2 2s^2 2p^6 3s^2 3p^1$
Comparison with Options
Option A: $1s^2 2s^2 2p^6 3s^2 3p^1$ (Total = 13) - Matches our calculation.
Option B: $1s^2 2s^2 2p^4 3p^1 3s^1$ (Total = 10) - Incorrect.
Option C: $1s^2 2s^2 2p^6 3s^2 3p^3$ (Total = 15) - Incorrect.
Option D: $1s^1 2s^2 2p^6 3s^2 3p^4$ (Total = 15) - Incorrect.
Exam Tip
When writing electronic configurations, always remember the "2-8-3" rule for the main shells (K, L, M). For element 13, the shells are 2, 8, and 3. If you look at the subshells in Option A, the 3rd shell ( $3s^2 3p^1$ ) contains $2 + 1 = 3$ electrons, which matches the valence electrons of Group 13 elements. This is a quick way to verify your answer!
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34.
Chlorine consisting of two isotope of mass number 35 and 37 in the ratio 3:1 has an atomic mass of 35.5. Calculate the relative abundance of the isotope of mass number 37
1. A.20
2. B.25
3. C.60
4. D.75
Show answer
Answer: B. 25
AI explanation
Analysis
The question asks for the relative abundance (percentage) of the chlorine isotope with a mass number of 37, given the ratio of the two isotopes ( $^{35}\text{Cl}$ and $^{37}\text{Cl}$ ) is 3:1.
Concept
Relative atomic mass is the weighted average of the masses of all naturally occurring isotopes of an element. The formula is:
$\text{Relative Atomic Mass} = \sum (\text{Isotope Mass} \times \text{Relative Abundance})$
Where the sum of the relative abundances must equal 100%.
Solution
Understand the Ratio: The isotopes are in the ratio 3:1. This means for every 4 atoms of chlorine, 3 are $^{35}\text{Cl}$ and 1 is $^{37}\text{Cl}$ .
Calculate the Total Parts: The total number of parts in the ratio is $3 + 1 = 4$ .
Calculate the Fraction of $^{37}\text{Cl}$ : The isotope with mass number 37 represents 1 part out of 4. $ $\text{Fraction} = \frac{1}{4}$ $
Convert to Percentage: To find the relative abundance (percentage), multiply the fraction by 100: $ $\text{Relative Abundance} = \left( \frac{1}{4} \right) \times 100\% = 25\%$ $
(Self-check: The relative abundance of $^{35}\text{Cl}$ would be $\frac{3}{4} \times 100\% = 75\%$ . Calculating the average mass: $(35 \times 0.75) + (37 \times 0.25) = 26.25 + 9.25 = 35.5$ . This confirms our calculation is correct.)
Conclusion
The relative abundance of the isotope with mass number 37 is 25%. This matches option B.
Exam Tip
When you see a ratio like $x:y$ , the percentage of the second component is always $\frac{y}{x+y} \times 100$ . Don't waste time doing complex algebraic equations if the ratio is already provided; simply convert the ratio parts into a percentage of the total!
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35.
A suitable reagent for distinguish between ethanoic and ethanol is
1. A.bromine water
2. B.Fehling’s solution
3. C.sodium hydrogen trioxocarbonate (iv)
4. D.Ammoniacal silver trioxonitrate(V)
Show answer
Answer: C. sodium hydrogen trioxocarbonate (iv)
AI explanation
1. Analyze the question
The goal is to identify a chemical reagent that reacts differently with ethanoic acid (a carboxylic acid) and ethanol (an alcohol). We need a substance that will produce a visible change (like effervescence) with one but not the other.
2. Explain the concept
Ethanoic acid ( $CH_3COOH$ ): As an acid, it reacts with carbonates and hydrogen carbonates to liberate carbon(IV) oxide gas ( $CO_2$ ). This gas causes effervescence (fizzing) when passed through limewater, turning it milky.
Ethanol ( $C_2H_5OH$ ): As a neutral organic compound (alcohol), it does not react with carbonates or hydrogen carbonates. Therefore, no gas is evolved.
3. Show the solution
Let's evaluate the options:
A. Bromine water: Used to test for unsaturation (alkenes/alkynes). Neither ethanol nor ethanoic acid reacts with it under normal conditions.
B. Fehling’s solution: Used to distinguish between aldehydes and ketones. Neither of these compounds is an aldehyde or ketone.
C. Sodium hydrogen trioxocarbonate(IV) ( $NaHCO_3$ ): This is a base. When added to ethanoic acid, the following reaction occurs: $CH_3COOH_{(aq)} + NaHCO_{3(s)} \rightarrow CH_3COONa_{(aq)} + H_2O_{(l)} + CO_{2(g)}$ The production of $CO_2$ gas (effervescence) confirms the presence of the acid. Ethanol does not react with $NaHCO_3$ .
D. Ammoniacal silver trioxonitrate(V) (Tollens' reagent): Used to test for aldehydes. Neither compound will give a positive "silver mirror" test.
4. Identify the answer
The correct reagent is sodium hydrogen trioxocarbonate(IV), because it reacts with the acidic group in ethanoic acid to produce bubbles of carbon(IV) oxide, while ethanol remains inert.
5. Exam Tip
Whenever you see a question asking to distinguish between an acid and another organic compound, always look for a carbonate or hydrogen carbonate in the options. These are the "gold standard" reagents for identifying carboxylic acids in JAMB Chemistry!
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36.
The basic particles from which matter could be made up of are as follow, except?
1. A.Salt
2. B.Atom
3. C.Ion
4. D.Molecule
Show answer
Answer: A. Salt
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37.
Cathode rays cause an object placed behind a perforated anode to cast a shadow on the screen. This observation shows that the rays
1. A.are positively charged
2. B.are negatively charged
3. C.Have mass
4. D.travel in straight lines
Show answer
Answer: D. travel in straight lines
AI explanation
Analysis of the Question
The question asks us to identify the physical property of cathode rays based on the observation that they cast a shadow of an object placed in their path.
Concept Explanation
Cathode rays are streams of electrons emitted from the cathode in a vacuum tube. To understand why they cast a shadow, we look at the principles of wave and particle motion:
Rectilinear Propagation: Light and certain particle beams travel in straight lines. If an opaque object is placed in the path of such a beam, the rays are blocked by the object, preventing them from reaching the screen behind it.
Shadow Formation: A shadow is formed only when a beam of radiation is obstructed by an object. If the rays were able to bend or curve around the object, a clear shadow would not be cast. Therefore, the presence of a sharp shadow is a classic experimental proof that the rays travel in a straight line.
Step-by-Step Solution
Examine the setup: We have a perforated anode and an object placed in the path of the rays.
Observe the effect: The rays hit the object and are blocked. Because the rays cannot "bend" around the object, the area behind the object remains dark (a shadow).
Relate to properties: • If they were simply charged, they would be deflected by electric or magnetic fields, but that doesn't explain the shadow. • If they had mass, that would be proven by their ability to rotate a paddle wheel, not by casting a shadow. • The formation of a shadow is the direct consequence of the rays moving in a straight-line path.
Conclusion
The observation that cathode rays cast a shadow confirms that they travel in straight lines. While cathode rays are indeed negatively charged (electrons) and possess mass, the specific observation of a "shadow" is the experimental evidence for their rectilinear (straight-line) propagation.
Exam Tip
When you see questions about cathode ray properties, remember these three key experiments:
Shadow formation: Proves they travel in straight lines.
Paddle wheel rotation: Proves they possess mass/momentum.
Deflection by electric/magnetic fields: Proves they are negatively charged.
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38.
An elements used in production of matches is
1. A.nitrogen
2. B.aluminum
3. C.copper
4. D.sulphur
Show answer
Answer: D. sulphur
AI explanation
Analysis
The question asks for the specific element used in the manufacturing of matches. We need to look at the chemical composition of match heads and the striking surface of a matchbox.
Concept Explanation
Matches work based on a chemical reaction between an oxidizing agent and a fuel.
Match heads: Typically contain an oxidizing agent (like potassium chlorate) and a fuel (like sulphur or antimony trisulphide).
Striking surface: Usually contains red phosphorus.
When the match is struck, the friction generates enough heat to convert a small amount of red phosphorus into white phosphorus, which ignites the potassium chlorate, providing the heat necessary to ignite the sulphur and the wooden stick.
Step-by-Step Solution
Evaluate Nitrogen (A): Nitrogen is an inert gas used in food packaging and light bulbs to prevent oxidation. It is not a component of match heads.
Evaluate Aluminum (B): Aluminum is a metal used in construction, alloys, and kitchen utensils. It is not used in the combustion process of matches.
Evaluate Copper (C): Copper is a transition metal used primarily for electrical wiring and plumbing. It does not play a role in the ignition chemistry of matches.
Evaluate Sulphur (D): Sulphur is a non-metal that acts as a fuel in the match head. It has a low ignition temperature, which allows the match to catch fire easily once the initial spark is created.
Conclusion
Based on the chemical composition of matches, sulphur is the essential element listed among the options that serves as a fuel in the match head.
Exam Tip: When dealing with questions about match production, remember the "Matchbox Trio": Red Phosphorus (on the box), Potassium Chlorate (oxidizer in the head), and Sulphur (fuel in the head). If you see any of these three in an exam question, they are likely your target answer!
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39.
In countries where the temperature fall below 273k, salt always spilled on the road in order to
1. A.increase the boiling point
2. B.increase the density of the ice
3. C.make the ice impure
4. D.reduce the freezing point of ice
Show answer
Answer: D. reduce the freezing point of ice
AI explanation
Analysis
The question asks for the scientific reason why salt (sodium chloride) is spread on icy roads in cold climates (where temperatures drop below 273K, which is 0°C).
Concept: Freezing Point Depression
This phenomenon is based on a colligative property of solutions known as Freezing Point Depression.
What is Freezing Point Depression? When a solute (like salt) is dissolved in a solvent (like water), the freezing point of the resulting solution becomes lower than that of the pure solvent.
How it works: The salt particles interfere with the ability of water molecules to arrange themselves into the rigid, crystalline structure of ice. Because the salt disrupts this process, the water needs to be cooled to a much lower temperature than 0°C before it can successfully turn into ice.
Application: By spreading salt on the road, the freezing point of the water/ice mixture is lowered. If the ambient temperature is, for example, -2°C, the salt might lower the freezing point of the ice to -5°C. Since the ambient temperature is now above the new freezing point, the ice melts into liquid water.
Step-by-Step Solution
Step 1: Identify the state of the road. It is covered in ice (solid water) at 273K (0°C) or below.
Step 2: Recognize the effect of adding salt. Salt acts as an impurity that dissolves in the thin layer of water on the ice surface.
Step 3: Apply the principle of colligative properties. The presence of the solute (salt) lowers the chemical potential of the liquid phase, making it harder for the water to freeze and easier for the ice to melt.
Step 4: Conclude the result. The freezing point of the ice is reduced, causing it to melt even if the air temperature remains below the standard freezing point of pure water.
Conclusion
Exam Tip: Remember that adding a solute to a solvent always lowers the freezing point and raises the boiling point. This is why we add salt to water when boiling pasta (to raise the boiling point) and why we add salt to icy roads (to lower the freezing point).
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40.
A fixed mass of gas occupies 92cm3 at 3°C. What will be its volume at 18C if the pressure remains constant?
1. A.15.3cm3
2. B.87.3cm3
3. C.2.0cm3
4. D.97.0cm3
Show answer
Answer: D. 97.0cm3
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41.
In the production of soap, concentrated sodium chloride solution is added to
1. A.increase the solubility of soap
2. B.decrease the solubility of the soap
3. C.saponify the soap
4. D.emulsify the soap
Show answer
Answer: B. decrease the solubility of the soap
AI explanation
Analysis
This question tests your understanding of the Saponification process, which is the industrial method of manufacturing soap by reacting fats or oils with an alkali (like sodium hydroxide).
Concept: Salting-out
In the soap-making process, the reaction produces a mixture of soap, glycerol, and water. To separate the soap from this mixture, we perform a process called "salting-out."
When concentrated sodium chloride (common salt) solution is added to the mixture, it increases the ionic strength of the solution. Soap is a salt of a long-chain fatty acid. According to the principle of common ion effect and solubility, the presence of a high concentration of $Na^+$ ions from the salt significantly reduces the solubility of the soap in the aqueous layer. As a result, the soap precipitates and floats to the top as a solid curd, making it easy to skim off.
Step-by-Step Solution
The Reaction: Fats/Oils + NaOH → Soap + Glycerol.
The Problem: At the end of the reaction, the soap is dissolved in the water/glycerol mixture.
The Action: We add concentrated sodium chloride (brine).
The Effect: The high concentration of ions makes the soap less soluble in the aqueous phase.
The Result: The soap "salts out" (precipitates) and separates from the liquid, allowing for collection.
Conclusion
Adding concentrated sodium chloride does not saponify the soap (that is the job of the alkali) nor does it emulsify it. Its primary purpose is to make the soap insoluble so it can be separated from the mixture.
The correct option is B.
Exam Tip
Whenever you see "sodium chloride" in the context of soap production in a JAMB question, immediately associate it with "salting-out" or "decreasing solubility." It is a classic separation technique!
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42.
Which of the following types of alkanols undergo oxidation to produce alkanoic acids. I. Primary alkanols II. Secondary alkanols III. Tertiary alkanols
1. A.I, II and III
2. B.I and II only
3. C.III only
4. D.I only
Show answer
Answer: D. I only
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43.This question needs a diagram, table or passage that we don't have yet, so it isn't shown.
44.
Which of the noble gases has the greatest ionization energy
1. A.He
2. B.Xe
3. C.Ar
4. D.Rr
Show answer
Answer: A. He
AI explanation
Analysis
The question asks for the noble gas with the greatest ionization energy. Ionization energy is the amount of energy required to remove the most loosely held electron from a neutral gaseous atom.
Concept Explanation
Periodic Trend: Ionization energy generally increases across a period (from left to right) and decreases down a group.
Atomic Size: As you move down a group in the periodic table, the number of electron shells increases. This means the outermost electrons are further away from the nucleus and are shielded by more inner-shell electrons.
Nuclear Attraction: Because the outermost electrons are further from the nucleus in larger atoms, the electrostatic attraction between the nucleus and these electrons is weaker. Therefore, it requires less energy to remove an electron from a larger atom than from a smaller one.
Noble Gases (Group 18): Helium (He) is at the top of the group, meaning it has the smallest atomic radius. Because its electrons are closest to the nucleus and experience the strongest nuclear pull, it requires the most energy to remove an electron.
Step-by-Step Solution
Step 1: Identify the positions of the elements in Group 18: • Helium (He) - Period 1 • Neon (Ne) - Period 2 • Argon (Ar) - Period 3 • Krypton (Kr) - Period 4 • Xenon (Xe) - Period 5 • Radon (Rn) - Period 6
Step 2: Apply the trend. Since ionization energy decreases as you go down the group, the element at the very top (Helium) will have the highest ionization energy.
Step 3: Compare the options provided. Helium (He) is the smallest noble gas, making its electrons the most tightly bound to the nucleus.
Conclusion
Helium has the smallest atomic radius among the noble gases, which results in the highest effective nuclear charge felt by its valence electrons. Consequently, it has the highest first ionization energy of all elements in the periodic table.
Exam Tip: Always remember the mnemonic "Up and Right": Ionization energy, electronegativity, and electron affinity generally increase as you move up a group and right across a period.
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45.
Chlorine gas turns damp starch-iodide paper
1. A.pink
2. B.colourless
3. C.red
4. D.dark blue
Show answer
Answer: D. dark blue
AI explanation
1. Analyze the question
The question asks for the observable change that occurs when chlorine gas comes into contact with damp starch-iodide paper. This is a classic test for oxidizing agents in chemistry.
2. Explain the concept
Chlorine ( $Cl_2$ ) is a powerful oxidizing agent. Starch-iodide paper contains potassium iodide ( $KI$ ) and starch. When an oxidizing agent like chlorine gas is introduced, it reacts with the iodide ions ( $I^-$ ) in the paper to produce free iodine ( $I_2$ ).
The chemical equation for this reaction is: $Cl_{2(g)} + 2I^-_{(aq)} \rightarrow 2Cl^-_{(aq)} + I_{2(s)}$
Once the free iodine is produced, it reacts with the starch present in the paper to form a deep blue-black complex. This reaction is a standard qualitative test used to detect the presence of oxidizing gases.
3. Show the solution
Step 1: Chlorine gas acts as an oxidizing agent.
Step 2: It displaces iodine from the potassium iodide in the damp paper.
Step 3: The liberated iodine reacts with the starch molecules.
Step 4: The starch-iodine complex creates a characteristic dark blue (or blue-black) color.
4. Identify the answer
Comparing our findings to the provided options: A. pink B. colourless C. red D. dark blue
The reaction produces a dark blue color. This matches option D.
5. Tip
Think of this as a "color-coded" test: Iodine + Starch = Blue-Black. Whenever you see "starch-iodide" in a question, immediately associate it with the detection of an oxidizing agent and the resulting dark blue color. This is a very common question in JAMB Chemistry, so keep it in your memory bank!
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46.
The number of isomers formed by C6H14 is
1. A.4
2. B.5
3. C.2
4. D.3
Show answer
Answer: B. 5
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47.
Alloys are best prepared by
1. A.electroplating
2. B.Arc-welding
3. C.reducing and mixture of their metallic
4. D.cooking a molten of the metals
Show answer
Answer: D. cooking a molten of the metals
AI explanation
Analysis of the Question
The question asks for the most effective method used to prepare alloys. An alloy is a homogeneous mixture of two or more metals (or a metal and a non-metal). To create this mixture, the components must be thoroughly combined at a molecular level.
Concept Explanation
An alloy is formed by combining metals in their molten (liquid) state. When metals are heated until they melt, their atoms gain enough kinetic energy to move freely. By mixing these molten metals together and then allowing the mixture to cool and solidify, the atoms become uniformly distributed throughout the solid structure. This process ensures the resulting material has the desired physical and chemical properties (like increased strength or corrosion resistance).
Step-by-Step Solution
Evaluate Option A (Electroplating): This is a process used to coat one metal with another using electricity. It does not create an alloy; it creates a surface layer.
Evaluate Option B (Arc-welding): This is a technique used to join two pieces of metal together using heat from an electric arc. While it involves melting, it is a joining process, not a method for creating a bulk alloy.
Evaluate Option C (Reducing and mixture of their metallic): This phrasing is grammatically incorrect and scientifically inaccurate. Reduction is a process used to extract metals from their ores, not to mix them into alloys.
Evaluate Option D (Cooking a molten of the metals): In chemistry, "cooking" in this context refers to the process of melting the metals together in a furnace (often called "melting" or "fusion"). By melting the constituent metals and stirring them together, you create a uniform liquid solution that forms an alloy upon cooling.
Conclusion
The most accurate way to describe the preparation of an alloy is by melting the metals together. While the phrasing in option D is slightly informal ("cooking"), it is the only option that correctly describes the process of fusion (melting) to create a metallic mixture.
Exam Tip: Whenever you see questions about alloys, remember the keyword "Fusion." Alloys are almost always prepared by the fusion of the constituent metals. If you see "melting" or "fusion" in the options, that is almost certainly your correct answer.
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48.
The acid in electrolysis of water is dilute
1. A.HNO3
2. B.CH3COOH
3. C.H2SO4
4. D.HCl
Show answer
Answer: C. H2SO4
AI explanation
Analysis
The question asks for the specific acid used to facilitate the electrolysis of water. Pure water is a poor conductor of electricity because it has very few ions. To make it conduct electricity effectively, we add a small amount of an electrolyte (an acid, base, or salt).
Concept
In the electrolysis of water, we aim to decompose water ( $H_2O$ ) into hydrogen gas and oxygen gas. The acid added must be non-volatile and must not interfere with the discharge of the hydrogen and hydroxide ions at the electrodes.
HNO₃ (Nitric acid): This is an oxidizing acid. It can interfere with the products formed at the electrodes.
CH₃COOH (Ethanoic acid): This is a weak acid and does not provide enough ions to make the water a good conductor.
H₂SO₄ (Tetraoxosulphate(VI) acid): This is a strong, non-volatile acid. It provides a high concentration of $H^+$ and $SO_4^{2-}$ ions, which increases the conductivity of the water without being consumed in the reaction or producing unwanted side products at the electrodes.
HCl (Hydrochloric acid): This is a volatile acid. During electrolysis, chloride ions ( $Cl^-$ ) would be preferentially discharged at the anode instead of hydroxide ions, leading to the production of chlorine gas instead of oxygen gas.
Solution
Requirement: We need an electrolyte that increases conductivity without being discharged itself.
Process: Dilute tetraoxosulphate(VI) acid ( $H_2SO_4$ ) is preferred because the sulphate ion ( $SO_4^{2-}$ ) is much harder to discharge than the hydroxide ion ( $OH^-$ ) from water.
Result: Consequently, $OH^-$ ions are discharged at the anode to produce oxygen, and $H^+$ ions are discharged at the cathode to produce hydrogen. This allows the electrolysis of water to proceed efficiently.
Tip
When choosing an electrolyte for electrolysis, always remember the Electrochemical Series. You want an electrolyte whose ions are "less easily discharged" than the ions of the solvent (water), so that the water itself is the substance being decomposed.
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49.
A liquid that will dissolve fat is
1. A.hydrochloric acid
2. B.calcium hydrochloride
3. C.kerosene
4. D.water
Show answer
Answer: C. kerosene
AI explanation
Analysis
The question asks for a substance capable of dissolving fat. In chemistry, the principle of "like dissolves like" is key: polar solvents dissolve polar solutes, and non-polar solvents dissolve non-polar solutes. Fats and oils are non-polar organic compounds.
Concept Explanation
Polarity: Water is a highly polar solvent. Because fats are non-polar, they do not mix or dissolve in water; instead, they form a separate layer (immiscible).
Acids/Salts: Hydrochloric acid and calcium hydrochloride are polar/ionic substances. They are generally used for chemical reactions or bleaching, not for dissolving non-polar fats.
Organic Solvents: Kerosene is a mixture of hydrocarbons. Hydrocarbons are non-polar organic compounds. Since both kerosene and fat are non-polar, kerosene acts as an effective solvent for fats and oils.
Step-by-Step Solution
Identify the nature of the solute: Fat is a non-polar organic molecule.
Evaluate the options: • A (Hydrochloric acid): An inorganic acid; it will not dissolve fat. • B (Calcium hydrochloride): An inorganic salt; it will not dissolve fat. • C (Kerosene): A non-polar organic solvent (hydrocarbon). It is chemically similar to fat, allowing it to break down and dissolve fat molecules. • D (Water): A polar solvent; it cannot dissolve non-polar fats.
Conclusion: Based on the principle of "like dissolves like," kerosene is the correct solvent for fat.
Correct Answer
The correct option is C.
Exam Tip
Whenever you see a question about "dissolving" in Chemistry, remember the golden rule: "Like dissolves like."
Water dissolves ionic salts and polar substances (like sugar).
Organic solvents (like kerosene, petrol, benzene, or ethanol) dissolve non-polar substances (like fats, oils, and grease).
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50.
Atomicity of ozone is
1. A.1
2. B.2
3. C.3
4. D.4
Show answer
Answer: C. 3
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51.
The gas that is most useful in protecting humans against solar marathon is
1. A.chlorine
2. B.ozone
3. C.carbon IV oxide
4. D.hydrogen sulphide
Show answer
Answer: B. ozone
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52.
N2O4(g)→ 2NO2(g) In the endothermic reaction above, more products formed will be favored by
1. A.A constant values
2. B.an increase in pressure
3. C.a decrease pressure
4. D.a decrease volume
Show answer
Answer: C. a decrease pressure
AI explanation
Analysis of the Question
This question tests your understanding of Le Chatelier’s Principle, which states that if a dynamic equilibrium is disturbed by changing the conditions (such as temperature, pressure, or concentration), the position of equilibrium shifts to counteract the change.
Concept Explanation
To determine how pressure affects an equilibrium reaction, we look at the number of moles of gas on both sides of the equation:
Reactant side: $N_2O_4(g)$ = 1 mole of gas.
Product side: $2NO_2(g)$ = 2 moles of gas.
Le Chatelier’s Principle regarding pressure:
Increasing pressure shifts the equilibrium toward the side with fewer moles of gas to reduce the pressure.
Decreasing pressure shifts the equilibrium toward the side with more moles of gas to increase the pressure.
Step-by-Step Solution
Identify the goal: We want to favor the formation of more products ( $2NO_2$ ).
Compare moles: The product side has 2 moles, while the reactant side has only 1 mole.
Apply the rule: To favor the side with more moles (the product side), we must decrease the pressure of the system.
Evaluate the options: • Increasing pressure (Option B) would favor the reactant side (1 mole). • Decreasing volume (Option D) is equivalent to increasing pressure, so it would also favor the reactant side. • Decreasing pressure (Option C) allows the system to shift toward the side with more moles to fill the space, thus favoring the production of $NO_2$ .
Conclusion
By decreasing the pressure, the system shifts to the right (the side with more gas molecules) to restore equilibrium, thereby producing more $NO_2$ .
Exam Tip
Think of pressure like a crowd in a room: if you increase the pressure (squeeze the room), the molecules will try to "clump together" into the side with fewer moles to save space. If you decrease the pressure (expand the room), the molecules will "spread out" into the side with more moles to fill the extra space!
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53.
What volume of 0.5mldm3 H2SO4 will exactly neutralize 20cm3 of 0.1moldm3 NaOH Solution?
1. A.2.0cm3
2. B.5.0cm3
3. C.6.8cm3
4. D.8.3cm3
Show answer
Answer: A. 2.0cm3
AI explanation
Analysis
To solve this problem, we need to use the principle of titration (neutralization). We are given the concentration and volume of a base (NaOH) and the concentration of an acid ( $H_2SO_4$ ). We need to find the volume of the acid required to neutralize the base.
Concept
The reaction between Sulfuric acid ( $H_2SO_4$ ) and Sodium hydroxide ( $NaOH$ ) is:
$H_2SO_4 + 2NaOH \rightarrow Na_2SO_4 + 2H_2O$
From the balanced equation, the mole ratio is:
$n_a$ (moles of acid) = 1
$n_b$ (moles of base) = 2
We use the titration formula:
$\frac{C_a V_a}{C_b V_b} = \frac{n_a}{n_b}$
Where:
$C_a$ = Concentration of acid = $0.5 \, \text{mol/dm}^3$
$V_a$ = Volume of acid = ?
$C_b$ = Concentration of base = $0.1 \, \text{mol/dm}^3$
$V_b$ = Volume of base = $20 \, \text{cm}^3$
Solution
Substitute the values into the formula: $ $\frac{0.5 \times V_a}{0.1 \times 20} = \frac{1}{2}$ $
Simplify the denominator: $ $\frac{0.5 \times V_a}{2} = \frac{1}{2}$ $
Cross-multiply to solve for $V_a$ : $ $2 \times (0.5 \times V_a) = 2 \times 1$ $ $ $1 \times V_a = 2$ $ $ $V_a = 2.0 \, \text{cm}^3$ $
Conclusion
The volume of $0.5 \, \text{mol/dm}^3$ $H_2SO_4$ required is $2.0 \, \text{cm}^3$ .
Exam Tip
Always remember to balance your chemical equation first! Many students forget the mole ratio ( $n_a/n_b$ ) and simply use $C_aV_a = C_bV_b$ . If you ignore the stoichiometry of the reaction, you will get the wrong answer. In this case, the $H_2SO_4$ is diprotic (has two $H^+$ ions), which is why the ratio is 1:2.
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54.
Which of the following compounds can be represented by the molecular formula C2 H6O?
1. A.propanal
2. B.ethanol
3. C.methanoic acid
4. D.glucose
Show answer
Answer: B. ethanol
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55.
Iron is often galvanized in order to
1. A.Make it more malleable
2. B.Remove the impurities unit
3. C.Protect it against corrosion
4. D.Render it passive
Show answer
Answer: C. Protect it against corrosion
AI explanation
Analysis
The question asks for the primary purpose of the industrial process known as galvanization when applied to iron.
Concept Explanation
Galvanization is a metallurgical process where a protective coating of zinc is applied to iron or steel.
Why Zinc? Zinc is more reactive than iron. When iron is exposed to air and moisture, it undergoes oxidation (rusting). By coating the iron with zinc, we create a "sacrificial anode."
How it works: Even if the zinc coating is scratched, the zinc will corrode in preference to the iron because it is more electropositive. This effectively prevents the iron underneath from rusting. This process is a common method used in Nigeria for protecting roofing sheets and iron pipes from the humid, corrosive environment.
Step-by-Step Solution
Evaluate Option A: Malleability is a physical property of metals. Galvanization creates a surface layer; it does not change the internal crystalline structure of iron to make it more malleable.
Evaluate Option B: Removing impurities is typically done during the extraction of iron from its ore (e.g., in a blast furnace), not by galvanizing the finished product.
Evaluate Option C: Corrosion is the gradual destruction of materials by chemical reaction with their environment (rusting). Since zinc prevents iron from reacting with oxygen and water, this is the primary purpose of galvanization.
Evaluate Option D: Rendering a metal "passive" refers to making it unreactive by forming a thin, non-porous oxide layer (like aluminum does naturally). Galvanization is an external coating process, not a passivation process.
Conclusion
The process of galvanization is specifically designed to prevent the oxidation of iron, which is commonly known as corrosion or rusting.
Exam Tip: Always remember the "Sacrificial Protection" concept. If you see a question about "galvanizing," immediately associate it with Zinc and Rust Prevention.
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56.
An oxidation state of Cr in K2Cr2O7
1. A.7
2. B.6
3. C.5
4. D.4
Show answer
Answer: B. 6
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57.
Detergents are manufactured with straight hydrocarbon chains, is to make them
1. A.soluble
2. B.biodegradable
3. C.cheaper
4. D.foamy
Show answer
Answer: B. biodegradable
AI explanation
Analysis
The question asks why manufacturers prefer using straight hydrocarbon chains when producing detergents. This is a classic environmental chemistry question often found in JAMB and WASSCE syllabi.
Concept Explanation
Detergents are synthetic cleaning agents. Early detergents were made with branched hydrocarbon chains. These branched chains were resistant to bacterial decomposition, meaning they did not break down easily in water bodies, leading to persistent water pollution and excessive foaming in rivers.
To solve this, manufacturers switched to straight-chain (linear) alkylbenzenes. Straight chains are much easier for microorganisms (bacteria) to break down. When a substance can be broken down by biological processes (like bacteria), it is said to be biodegradable.
Step-by-Step Solution
Identify the problem: Branched-chain detergents cause environmental pollution because they are "non-biodegradable" (they persist in the environment).
Analyze the solution: By using straight hydrocarbon chains, the molecular structure becomes more accessible to the enzymes produced by bacteria.
Connect to the options: • Solubility (A): While straight chains affect solubility, the primary manufacturing goal for using them is environmental safety. • Biodegradability (B): Straight chains allow bacteria to break the molecules down into simpler, harmless substances. • Cost (C): Straight-chain detergents are often more expensive to produce than branched ones, so this is not the reason. • Foaming (D): Both branched and straight chains produce foam; the straight chain does not make it "more" foamy.
Conclusion
The primary reason for using straight hydrocarbon chains in the production of detergents is to ensure they can be broken down by microorganisms in the environment, preventing pollution.
Exam Tip: Always remember the "Straight = Biodegradable" rule for detergents. If you see a question about "branched" chains, the answer is almost always that they are "non-biodegradable" or cause "water pollution."
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58.
Which of the following results in the fall of acid rain?
1. A.oxide of lead
2. B.particulate matter
3. C.oxides of sulphur
4. D.gaseous hydrocarbon
Show answer
Answer: C. oxides of sulphur
AI explanation
Analysis
The question asks for the primary pollutant responsible for the phenomenon known as "acid rain." Acid rain occurs when certain gases react with water vapor in the atmosphere to form acidic solutions that fall to the earth.
Concept Explanation
Acid rain is primarily caused by the emission of non-metallic oxides into the atmosphere. When these oxides (specifically oxides of sulphur and nitrogen) react with water ( $H_2O$ ) in the clouds, they form strong acids.
Sulphur dioxide ( $SO_2$ ): When released from the burning of fossil fuels (like coal and oil), it reacts with oxygen and water in the atmosphere to form sulphuric acid ( $H_2SO_4$ ).
Nitrogen oxides ( $NO_x$ ): These also contribute to the formation of nitric acid ( $HNO_3$ ).
These acids lower the pH of rainwater, making it acidic, which can damage buildings, harm aquatic life, and degrade soil quality.
Step-by-Step Solution
Evaluate Option A (Oxide of lead): Lead oxides are toxic heavy metal pollutants but do not significantly contribute to the acidity of rain.
Evaluate Option B (Particulate matter): These are solid or liquid particles suspended in the air (like dust or soot). While they cause air pollution and respiratory issues, they are not the primary chemical cause of acid rain.
Evaluate Option C (Oxides of sulphur): Sulphur dioxide ( $SO_2$ ) and sulphur trioxide ( $SO_3$ ) are the main culprits. They dissolve in rainwater to produce sulphurous and sulphuric acids. This is the classic cause of acid rain taught in the chemistry syllabus.
Evaluate Option D (Gaseous hydrocarbon): Hydrocarbons contribute to smog and the greenhouse effect, but they do not directly form acids when reacting with water vapor.
Conclusion
Based on the chemical processes involved in atmospheric pollution, oxides of sulphur are the primary agents responsible for the formation of acid rain.
Exam Tip: Whenever you see "Acid Rain" in a JAMB or WASSCE question, immediately look for Oxides of Sulphur ( $SO_2$ ) or Oxides of Nitrogen ( $NO_2$ ). If both are present, they are both correct, but usually, one is provided as the primary answer.
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59.
The furring of kettles is caused by the presence of what compound in water?
1. A.calcium tetraoxosulphate (IV)
2. B.calcium hydrogentrioxocarbonate (IV)
3. C.calcium hydroxide
4. D.calcium trioxocarbonate (IV)
Show answer
Answer: B. calcium hydrogentrioxocarbonate (IV)
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60.
Calculate the relative molecular mass of Limestone CaCO3, (Ca = 40, C =12, O = 16)
1. A.56
2. B.100
3. C.76
4. D.90
Show answer
Answer: B. 100
AI explanation
Analysis
To find the relative molecular mass (also known as molar mass) of a compound, you must sum the relative atomic masses of all the individual atoms present in the chemical formula.
Concept
The formula for Limestone is CaCO₃. This means one molecule consists of:
1 atom of Calcium (Ca)
1 atom of Carbon (C)
3 atoms of Oxygen (O)
The formula to calculate the total mass is:
$\text{Relative Molecular Mass} = (\text{Number of Ca} \times \text{Mass of Ca}) + (\text{Number of C} \times \text{Mass of C}) + (\text{Number of O} \times \text{Mass of O})$
Step-by-Step Solution
Identify the atomic masses provided: • Ca = 40 • C = 12 • O = 16
Substitute the values into the formula: • Mass of Ca = $1 \times 40 = 40$ • Mass of C = $1 \times 12 = 12$ • Mass of O = $3 \times 16 = 48$ (Since there are 3 oxygen atoms)
Sum the values: • Total Mass = $40 + 12 + 48$ • Total Mass = $100$
The calculation confirms that the relative molecular mass of CaCO₃ is 100.
Exam Tip
When calculating molecular mass, always pay close attention to the subscripts (the small numbers after an element). A common mistake is forgetting to multiply the mass of Oxygen by 3. Always write out the count of each atom before you start multiplying to avoid silly errors!
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61.
A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen. If the molar mass of the compound is 180, Find the molecular formula [H = 1, C = 12, O = 16)
1. A.CH2O
2. B.C3H6O3
3. C.C6H12O6
4. D.C6H12O3
Show answer
Answer: C. C6H12O6
AI explanation
To find the molecular formula of this compound, we follow a systematic two-part process: first, finding the empirical formula, and then finding the molecular formula.
1. Determine the Empirical Formula
Assume we have 100g of the compound. This means we have:
Carbon (C): 40.0g
Hydrogen (H): 6.7g
Oxygen (O): 53.3g
Next, divide each mass by its relative atomic mass to find the number of moles:
Moles of C: $40.0 / 12 = 3.33$
Moles of H: $6.7 / 1 = 6.7$
Moles of O: $53.3 / 16 = 3.33$
Now, divide each value by the smallest result (which is 3.33) to get the simplest ratio:
C: $3.33 / 3.33 = 1$
H: $6.7 / 3.33 \approx 2$
O: $3.33 / 3.33 = 1$
The empirical formula is $CH_2O$ .
2. Determine the Molecular Formula
The molecular formula is a multiple ( $n$ ) of the empirical formula. We use the formula: $n = \text{Molar Mass} / \text{Empirical Formula Mass}$
Empirical Formula Mass ( $CH_2O$ ): $(12 \times 1) + (1 \times 2) + (16 \times 1) = 12 + 2 + 16 = 30$
$n$ : $180 / 30 = 6$
Now, multiply the empirical formula by $n$ : Molecular Formula $= 6 \times (CH_2O) = \mathbf{C_6H_{12}O_6}$
Conclusion
Comparing our result to the options provided: A. $CH_2O$ (This is the empirical formula) B. $C_3H_6O_3$ C. $C_6H_{12}O_6$ D. $C_6H_{12}O_3$
The correct option is C.
Exam Tip: When calculating the mole ratio, if you get a decimal like 1.5, multiply all values by 2 to get whole numbers. If you get 1.33, multiply by 3. In this question, the values were very close to whole numbers, making it straightforward!
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62.
A major source of oxide of nitrogen is from the burning of
1. A.coal
2. B.wood
3. C.fuel
4. D.chlorofluorocarbons
Show answer
Answer: C. fuel
AI explanation
1. Analyze the question
The question asks for the primary source of nitrogen oxides ( $NO_x$ ) released into the atmosphere through combustion processes. We need to identify which of the provided options is most associated with the high-temperature combustion that facilitates the reaction between atmospheric nitrogen and oxygen.
2. Explain the concept
Nitrogen oxides (primarily $NO$ and $NO_2$ ) are formed during combustion processes when nitrogen and oxygen from the air react at very high temperatures. This reaction is represented as:
$N_{2(g)} + O_{2(g)} \rightarrow 2NO_{(g)}$
In the context of environmental chemistry, the burning of fossil fuels in internal combustion engines (like those in cars, trucks, and power plants) is the most significant anthropogenic source of nitrogen oxides. While coal and wood contain some nitrogen, the combustion of liquid petroleum fuel (hydrocarbons) in engines operating at high temperatures and pressures is the classic source taught in the Nigerian secondary school chemistry curriculum regarding air pollution.
3. Show the solution
Coal (A): While burning coal releases sulfur dioxide ( $SO_2$ ) and carbon dioxide, it is not the primary source of nitrogen oxides compared to internal combustion engines.
Wood (B): Burning wood releases carbon monoxide and particulate matter, but it is not the major industrial source of $NO_x$ .
Fuel (C): The combustion of fossil fuels (petrol, diesel) in automobile engines is the leading cause of nitrogen oxide emissions. The high temperature of the engine forces the nitrogen in the air to react with oxygen.
Chlorofluorocarbons (D): These are refrigerants and propellants; they are responsible for ozone layer depletion, not the production of nitrogen oxides.
4. Identify the answer
The correct option is C.
5. Tip
Exam Strategy: When you see questions about "oxides of nitrogen" in the context of pollution, always look for keywords like "automobile exhaust," "internal combustion engines," or "fossil fuels." Remember that $SO_2$ is usually linked to "burning coal/sulfur," while $NO_x$ is linked to "high-temperature combustion of fuels."
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63.
The oxidation state of sulphur on H2SO4 acid is
1. A.-4
2. B.+6
3. C.4
4. D.-8
Show answer
Answer: B. +6
AI explanation
Analysis
To find the oxidation state of sulphur (S) in sulphuric acid ( $H_2SO_4$ ), we apply the rule that the sum of the oxidation states of all atoms in a neutral compound must equal zero.
Concept
Hydrogen (H): In most compounds, hydrogen has an oxidation state of +1.
Oxygen (O): In most compounds, oxygen has an oxidation state of -2.
Sulphur (S): This is the unknown element we need to solve for. Let its oxidation state be represented by $x$ .
Step-by-Step Solution
Write the formula: The compound is $H_2SO_4$ .
Set up the equation: $(2 \times \text{Oxidation state of H}) + (1 \times \text{Oxidation state of S}) + (4 \times \text{Oxidation state of O}) = 0$
Substitute the known values: $(2 \times +1) + (x) + (4 \times -2) = 0$
Simplify the expression: $2 + x - 8 = 0$
Solve for $x$ : $x - 6 = 0$ $x = +6$
The oxidation state of sulphur in $H_2SO_4$ is +6.
Conclusion
Comparing our result to the given options, the correct choice is B.
Exam Tip
Always remember that for neutral molecules, the sum is zero, but if you were dealing with a polyatomic ion (like $SO_4^{2-}$ ), the sum would be equal to the charge of the ion (in this case, -2). This simple distinction helps you solve oxidation state questions for both molecules and radicals!
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64.
what is the pH of 0.00lmoldm3 solution of sodium hydroxide
1. A.14
2. B.13
3. C.12
4. D.11
Show answer
Answer: D. 11
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2015 JAMB Chemistry Past Questions

Questions

Analysis

Concept Explanation

Step-by-Step Solution

Conclusion

Analysis of the Question

Concept Explanation

Step-by-Step Solution

Exam Tip

1. Analyze the question

2. Explain the concept

3. Show the solution

4. Identify the answer

5. Exam Tip

Analysis

Concept

Step-by-Step Solution

Conclusion

Exam Tip

Analysis

Concept

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Exam Tip

Analysis

Concept: Flame Test

Step-by-Step Solution

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Conclusion

Exam Tip

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Exam Tip

1. Analyze the question

2. Explain the concept

3. Show the solution

4. Identify the answer

5. Tip

Analysis

Concept

Step-by-Step Solution

Conclusion

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Analysis

Concept Explanation

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Conclusion

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Concept

Solution

Correct Answer

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Analysis

Concept: Effect of Pressure on Equilibrium

Step-by-Step Solution

Evaluation of Options

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Concept Explanation

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Conclusion

Exam Tip

Analysis

Concept Explanation

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Conclusion

Analysis of the Question

Concept Explanation

Step-by-Step Solution

Identification of the Answer

Exam Tip

Analysis

Concept Explanation

Step-by-Step Solution