2023 JAMB Chemistry Past Questions and Answers

Questions 1–41

1. 1.

   Which of the following compounds is an example of an electrovalent bond?

   1. A.NaCl (sodium chloride)
   2. B.CO2 (carbon dioxide)
   3. C.H2O (water)
   4. D.CH4 (methane)

   Show answer

   Answer: A. NaCl (sodium chloride)

   AI explanation

   Analysis

   The question asks us to identify which of the given compounds is formed by an electrovalent bond (also known as an ionic bond).

   Concept Explanation

   An electrovalent (ionic) bond is formed through the complete transfer of electrons from one atom to another. This typically occurs between:

   • Metals (which lose electrons to become positive ions/cations)
   • Non-metals (which gain electrons to become negative ions/anions)

   In contrast, covalent bonds (found in options B, C, and D) are formed by the sharing of electrons between non-metal atoms.

   Step-by-Step Solution

   1. Analyze NaCl: Sodium (Na) is a Group 1 metal. Chlorine (Cl) is a Group 7 non-metal. Sodium transfers one electron to Chlorine to achieve a stable octet configuration. This electrostatic attraction between the resulting $Na^+$ and $Cl^-$ ions forms an ionic (electrovalent) bond.
   2. Analyze $CO_2$: Carbon and Oxygen are both non-metals. They share electrons to form covalent bonds.
   3. Analyze $H_2O$: Hydrogen and Oxygen are both non-metals. They share electrons to form covalent bonds.
   4. Analyze $CH_4$: Carbon and Hydrogen are both non-metals. They share electrons to form covalent bonds.

   Since NaCl is the only compound formed by the transfer of electrons between a metal and a non-metal, it is the only electrovalent compound listed.

   Identification of Answer

   The correct option is A.

   Exam Tip

   A quick way to spot an electrovalent compound in JAMB Chemistry is to look for a compound containing a Group 1 or Group 2 metal bonded to a non-metal. If you see only non-metals (like C, H, O, N, S), it is almost certainly a covalent compound!

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2. 2.

   A gas occupies a volume of 1.5 liters at a pressure of 2 atmospheres. If the pressure is increased to 4 atmospheres while the temperature remains constant, what will be the new volume of the gas?

   1. A.6 liters
   2. B.1.5 liters
   3. C.0.75 liters
   4. D.3 liters

   Show answer

   Answer: C. 0.75 liters

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3. 3.

   What is the symbol used to represent an alpha particle?

   1. A.α
   2. B.γ
   3. C.δ
   4. D.β

   Show answer

   Answer: A. α

   AI explanation

   1. Analyze the question

   The question asks for the standard scientific symbol used to represent an alpha particle in nuclear chemistry.

   2. Explain the concept

   In nuclear chemistry, radioactive decay involves the emission of particles from an unstable nucleus. The three most common types of radiation are:

   • Alpha ($\alpha$) particles: These are helium nuclei consisting of two protons and two neutrons. They are represented by the Greek letter alpha ($\alpha$) or as $^4_2\text{He}$.
   • Beta ($\beta$) particles: These are high-energy electrons emitted from the nucleus. They are represented by the Greek letter beta ($\beta$) or as $^0_{-1}e$.
   • Gamma ($\gamma$) rays: These are high-energy electromagnetic waves. They are represented by the Greek letter gamma ($\gamma$).

   3. Show the solution

   • Option A ($\alpha$): This is the correct symbol for an alpha particle.
   • Option B ($\gamma$): This is the symbol for gamma radiation.
   • Option C ($\delta$): This is the Greek letter delta, which is not used to represent a standard nuclear decay particle.
   • Option D ($\beta$): This is the symbol for a beta particle.

   Since the question specifically asks for the alpha particle, the correct symbol is $\alpha$.

   4. Identify the answer

   The correct option is A.

   5. Tip

   To remember these, think of the Greek alphabet order: Alpha ($\alpha$) is the first letter, and alpha particles are the "heaviest" and most ionizing of the three. Beta ($\beta$) is the second letter, and Gamma ($\gamma$) is the third. Always look closely at the Greek symbols in your exam booklet to avoid mixing them up!

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4. 4.

   Stainless steel is an alloy made up of

   1. A.Iron and zinc
   2. B.Copper and tin
   3. C.Iron and chromium
   4. D.Iron and carbon

   Show answer

   Answer: C. Iron and chromium

   AI explanation

   Analysis

   The question asks for the composition of stainless steel, which is a common alloy in Chemistry. To answer this, we must identify the primary metallic components that give stainless steel its characteristic resistance to corrosion and rust.

   Concept

   An alloy is a mixture of two or more elements, where at least one is a metal. Stainless steel is a specific type of steel designed to resist oxidation. While all steel contains iron and a small amount of carbon, "stainless" steel is specifically defined by the addition of chromium. Chromium reacts with oxygen to form a thin, invisible layer of chromium oxide on the surface, which prevents further rusting of the iron underneath.

   Solution

   1. Identify the base: All steels are primarily composed of Iron (Fe).
   2. Identify the key additive: The "stainless" property is provided by Chromium (Cr). Typically, stainless steel contains at least 10.5% chromium.
   3. Evaluate the options: • A (Iron and zinc): This describes galvanized iron, not stainless steel. • B (Copper and tin): This is the composition of bronze. • C (Iron and chromium): This is the correct definition of the primary components of stainless steel (often with small amounts of nickel and carbon added). • D (Iron and carbon): This is the definition of plain carbon steel.

   Conclusion

   Stainless steel is primarily an alloy of iron and chromium. While carbon is present in small amounts in almost all steel, the defining characteristic that makes it "stainless" is the chromium content. Therefore, option C is the most accurate description among the choices provided.

   Exam Tip: Remember the mnemonic "Stainless = Chromium." Whenever you see a question about stainless steel, look for Chromium in the options. If you see "Iron and Carbon," that is just regular steel; the Chromium is what makes it "stainless."

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5. 5.

   Which element is placed at the top of the electrochemical series?

   1. A.Copper
   2. B.Hydrogen
   3. C.Sodium
   4. D.Oxygen

   Show answer

   Answer: C. Sodium

   AI explanation

   1. Analyze the question

   The question asks for the element positioned at the very top of the electrochemical series. In chemistry, the electrochemical series (or activity series) ranks elements based on their standard electrode potentials, specifically their tendency to lose electrons (oxidation) or gain electrons (reduction).

   2. Explain the concept

   The electrochemical series is a list of elements arranged in order of their standard electrode potentials ($E^0$).

   • Top of the series: Elements at the top are the strongest reducing agents. They have the most negative standard electrode potentials, meaning they lose electrons very easily and are highly reactive. These are typically the alkali and alkaline earth metals (e.g., Potassium, Sodium, Calcium).
   • Bottom of the series: Elements at the bottom are the strongest oxidizing agents. They have the most positive standard electrode potentials, meaning they hold onto their electrons tightly and are less reactive (e.g., Gold, Silver, Copper).
   • Hydrogen: Hydrogen is used as the reference point in the series with a standard electrode potential of $0.00\text{ V}$.

   3. Show the solution

   Let's evaluate the options provided based on their positions in the electrochemical series:

   • Copper (Cu): Located below Hydrogen. It is a poor reducing agent.
   • Hydrogen (H): Located in the middle of the series (the reference point).
   • Sodium (Na): Located very high up in the series. It is a highly reactive metal that loses electrons readily to form $\text{Na}^+$.
   • Oxygen (O): While involved in redox reactions, it is generally not categorized as a metal in the standard electrochemical series of metals.

   Comparing the options, Sodium is the most reactive metal listed and occupies a position significantly higher than Hydrogen and Copper. While Potassium and Lithium are actually at the very top of the full series, among the choices provided, Sodium is the correct representative of the highly reactive metals at the top.

   4. Identify the answer

   The correct option is C.

   5. Tip

   To remember the order of the most common metals in the electrochemical series, use this mnemonic: Please Stop Calling Me A Careless Zebra Instead Learn How Copper Saves Gold.

   • Potassium, Sodium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Lead, Hydrogen, Copper, Silver, Gold.

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6. 6.

   What is the common name for ethanoic acid?

   1. A.Acetic acid
   2. B.Butyric acid
   3. C.Propionic acid
   4. D.Formic acid

   Show answer

   Answer: A. Acetic acid

   AI explanation

   Analysis

   The question asks for the common (trivial) name of ethanoic acid, which is a carboxylic acid with the chemical formula $CH_3COOH$.

   Concept Explanation

   In organic chemistry, compounds often have two types of names:

   1. IUPAC Name: Based on a systematic set of rules (e.g., ethanoic acid). The prefix "eth-" indicates two carbon atoms, and the suffix "-oic acid" indicates a carboxylic acid group.
   2. Common (Trivial) Name: Based on the historical source or origin of the compound. For carboxylic acids, these names are often derived from Latin or Greek words related to where the acid was first discovered.

   Step-by-Step Solution

   1. Identify the structure: Ethanoic acid has two carbon atoms ($CH_3COOH$).
   2. Recall the origin: Ethanoic acid is the primary component of vinegar (aside from water). The Latin word for vinegar is acetum.
   3. Match the common name: Because it is the acid found in vinegar, it is historically and commonly referred to as acetic acid.

   Let's look at the other options to be sure:

   • Butyric acid: This is the common name for butanoic acid (4 carbons). It is associated with the smell of rancid butter.
   • Propionic acid: This is the common name for propanoic acid (3 carbons).
   • Formic acid: This is the common name for methanoic acid (1 carbon). It is associated with ant stings (the Latin word for ant is formica).

   Conclusion

   The common name for ethanoic acid is acetic acid.

   Exam Tip

   To remember these quickly, associate the common names with their sources:

   • Formic acid = Formica (Ants)
   • Acetic acid = Acetum (Vinegar)
   • Butyric acid = Butyrum (Butter)

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7. 7.

   What type of reaction is involved in the formation of alkanols from alkenes?

   1. A.Elimination reaction
   2. B.Redox reaction
   3. C.Substitution reaction
   4. D.Addition reaction

   Show answer

   Answer: D. Addition reaction

   AI explanation

   Analysis

   The question asks for the classification of the chemical reaction that converts an alkene (a hydrocarbon with a carbon-carbon double bond) into an alkanol (an alcohol).

   Concept Explanation

   To understand this, we look at the functional group transformation:

   • Alkenes contain a double bond ($C=C$). This double bond is a site of high electron density, making it reactive.
   • Alkanols contain a hydroxyl group ($-OH$).
   • The process of converting an alkene to an alkanol is typically hydration, where water ($H_2O$) is added across the double bond in the presence of an acid catalyst (like $H_3PO_4$).

   Because the double bond is "broken" to allow the atoms of the water molecule ($H$ and $OH$) to attach to the carbon atoms, the reaction is classified as an addition reaction. In an addition reaction, two or more molecules combine to form a single, larger molecule without the loss of any atoms.

   Step-by-Step Solution

   1. Identify the reactants: An alkene (e.g., ethene, $CH_2=CH_2$) and water ($H_2O$).
   2. Observe the change: $$CH_2=CH_2 + H_2O \xrightarrow{H^+} CH_3CH_2OH$$
   3. Analyze the mechanism: The double bond between the carbons is converted into a single bond. The hydrogen atom ($H$) from the water attaches to one carbon, and the hydroxyl group ($OH$) attaches to the other.
   4. Classify the reaction: Since atoms are being added to the molecule to saturate the double bond, this is definitively an addition reaction.

   • Elimination is the reverse (removing atoms to form a double bond).
   • Substitution involves replacing one atom with another (common in alkanes).
   • Redox involves electron transfer, which is not the primary classification for hydration.

   Conclusion

   The formation of alkanols from alkenes involves the addition of water across the double bond. Therefore, it is an addition reaction.

   Exam Tip

   Whenever you see a reaction where a double or triple bond is converted into a single bond, it is almost always an addition reaction. Think of it as "adding" atoms to the "open" spaces created by breaking the extra bonds!

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8. 8.

   Which of the following mixtures is an example of a colloid?

   1. A.Milk
   2. B.Orange juice
   3. C.Saltwater
   4. D.Sugar dissolved in water

   Show answer

   Answer: A. Milk

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9. 9.

   What is the name of the process by which ammonia is produced on an industrial scale?

   1. A.Nitrogenation
   2. B.Ammoniation
   3. C.Nitrification
   4. D.Haber process

   Show answer

   Answer: D. Haber process

   AI explanation

   Analysis

   The question asks for the specific industrial method used to synthesize ammonia ($NH_3$) from its constituent elements, nitrogen and hydrogen.

   Concept Explanation

   In industrial chemistry, the production of ammonia is a classic example of a reversible exothermic reaction. The process involves reacting nitrogen gas ($N_2$) obtained from fractional distillation of liquid air with hydrogen gas ($H_2$) obtained from natural gas (methane).

   The chemical equation for this reaction is:

   $N_{2(g)} + 3H_{2(g)} \rightleftharpoons 2NH_{3(g)}$

   This reaction is carried out under specific conditions to maximize yield:

   • Temperature: About 400°C – 450°C.
   • Pressure: High pressure (about 200 atmospheres).
   • Catalyst: Finely divided iron.

   This method was developed by the German chemist Fritz Haber and later scaled for industrial use by Carl Bosch.

   Step-by-Step Solution

   1. Evaluate Option A (Nitrogenation): This term is not standard in industrial chemistry for ammonia production; it usually refers to the introduction of nitrogen into a compound.
   2. Evaluate Option B (Ammoniation): This refers to the addition of ammonia to a substance, not the production of ammonia itself.
   3. Evaluate Option C (Nitrification): This is a biological process where bacteria convert ammonia into nitrites and nitrates in the soil.
   4. Evaluate Option D (Haber process): This is the internationally recognized name for the industrial synthesis of ammonia from nitrogen and hydrogen.

   Conclusion

   The Haber process is the correct industrial method for producing ammonia.

   Exam Tip: When studying industrial processes, always remember the "Big Three" for JAMB:

   • Haber Process: Ammonia ($NH_3$)
   • Contact Process: Sulphuric Acid ($H_2SO_4$)
   • Solvay Process: Sodium Carbonate ($Na_2CO_3$)

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10. 10.

    Which separation technique is used to separate different pigments in a mixture based on their affinity for a stationary phase and a mobile phase?

    1. A.Chromatography
    2. B.Filtration
    3. C.Decantation
    4. D.Distillation

    Show answer

    Answer: A. Chromatography

    AI explanation

    1. Analyze the question

    The question asks for a specific separation technique that relies on the movement of components (pigments) through a system involving two phases: a stationary phase (which stays still) and a mobile phase (which moves).

    2. Explain the concept

    This process is based on the principle of differential migration. In a mixture, different components have different chemical properties (such as polarity or solubility).

    • Stationary Phase: A solid or liquid supported on a solid that remains fixed in place.
    • Mobile Phase: A solvent or gas that flows through the stationary phase, carrying the mixture with it.

    As the mobile phase moves, the components of the mixture travel at different speeds depending on how strongly they "stick" to the stationary phase versus how well they dissolve in the mobile phase. This causes the pigments to separate into distinct bands or spots.

    3. Show the solution

    • Filtration: Used to separate an insoluble solid from a liquid (e.g., sand from water). It does not involve a mobile/stationary phase interaction.
    • Decantation: Used to separate a liquid from a settled solid by pouring off the top layer. It is a mechanical separation, not based on phase affinity.
    • Distillation: Used to separate components of a mixture based on differences in their boiling points.
    • Chromatography: Specifically designed to separate mixtures by distributing the components between a stationary phase and a mobile phase. This is the standard method used in laboratories to separate plant pigments (like chlorophyll and carotenoids).

    4. Identify the answer

    Based on the principles of separation science, the technique described is Chromatography.

    5. Exam Tip

    Think of chromatography as a "race." The pigments are the runners. The stationary phase is the track, and the mobile phase is the wind pushing them. Some pigments are "heavier" or "stickier" (high affinity for the stationary phase) and move slowly, while others are "lighter" or more soluble in the solvent (high affinity for the mobile phase) and move quickly. This difference in speed is what separates them!

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11. 11.

    When anhydrous cobalt chloride paper is exposed to water, what color change is observed?

    1. A.From pink to blue
    2. B.From white to blue
    3. C.From blue to white
    4. D.From blue to pink

    Show answer

    Answer: D. From blue to pink

    AI explanation

    Analysis

    The question asks for the color change that occurs when anhydrous cobalt(II) chloride ($CoCl_2$) reacts with water. This is a classic test for the presence of water in chemistry.

    Concept

    • Anhydrous Cobalt(II) Chloride ($CoCl_2$): The term "anhydrous" means "without water." In this state, cobalt(II) chloride exists as a blue crystalline solid.
    • Hydrated Cobalt(II) Chloride ($CoCl_2 \cdot 6H_2O$): When water is added to the anhydrous salt, it absorbs the water molecules to form a hydrated complex. This hydration process changes the electronic environment of the cobalt ions, resulting in a distinct color change to pink.
    • The Reaction: $CoCl_2(s) \text{ (blue)} + 6H_2O(l) \rightarrow CoCl_2 \cdot 6H_2O(s) \text{ (pink)}$

    Step-by-Step Solution

    1. Identify the starting state: Anhydrous cobalt chloride is blue.
    2. Identify the process: Exposure to water causes the substance to become hydrated.
    3. Identify the final state: Hydrated cobalt chloride is pink.
    4. Determine the direction of change: The color shifts from the initial state (blue) to the final state (pink).

    Conclusion

    Comparing this to the provided options, the change is from blue to pink.

    Exam Tip: Remember the mnemonic "Blue to Pink, Water's in the sink!" This helps you recall that the blue anhydrous paper turns pink when it detects moisture. Also, note that this process is reversible; if you heat the pink hydrated cobalt chloride, it will lose its water of crystallization and turn back to blue.

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12. 12.

    What is Faraday's constant?

    1. A.6.022 x 10$^{23}$ mol$^{-1}$
    2. B.3.00 x 10$^8$ m/s
    3. C.9.81 m/s$^2$
    4. D.96,485 C/mol

    Show answer

    Answer: D. 96,485 C/mol

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13. 13.

    Which type of chemical combination involves the transfer of electrons from one atom to another, resulting in the formation of oppositely charged ions?

    1. A.Ionic bonding
    2. B.Hydrogen bonding
    3. C.Covalent bonding
    4. D.Metallic bonding

    Show answer

    Answer: A. Ionic bonding

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14. 14.

    Why is water often referred to as the "universal solvent"?

    1. A.Water is the most abundant substance on Earth
    2. B.Water is essential for all living organisms.
    3. C.Water is involved in many chemical reactions
    4. D.Water can dissolve a wide variety of substances due to its polar nature

    Show answer

    Answer: D. Water can dissolve a wide variety of substances due to its polar nature

    AI explanation

    Analysis

    The question asks for the scientific reason behind the classification of water as the "universal solvent." We need to look at the chemical properties of water that allow it to interact with and dissolve many different types of solutes.

    Concept Explanation

    Water ($H_2O$) is a polar molecule. This means it has a partial positive charge ($\delta+$) on the hydrogen atoms and a partial negative charge ($\delta-$) on the oxygen atom.

    Because of this polarity:

    1. Electrostatic Attraction: Water molecules can surround and pull apart ionic compounds (like salt, $NaCl$) by attracting the positive ions to the oxygen end and negative ions to the hydrogen end.
    2. Hydrogen Bonding: Water can form hydrogen bonds with other polar molecules (like sugar or alcohols), allowing them to dissolve easily.
    3. Versatility: Because it can interact with both ionic and polar covalent substances, it is capable of dissolving a broader range of substances than almost any other common liquid.

    Step-by-Step Solution

    • Evaluate Option A: While water is abundant, its abundance does not explain its ability to dissolve substances.
    • Evaluate Option B: Being essential for life is a biological importance of water, but it is not the chemical definition of a "solvent."
    • Evaluate Option C: While water is a reactant in many reactions (like hydrolysis), this is a chemical property, not the reason it is called a "universal solvent."
    • Evaluate Option D: This directly addresses the chemical mechanism. The polar nature of the water molecule allows it to interact with the charges of other molecules, breaking their bonds and incorporating them into the solution. This is the fundamental reason for its solvent power.

    Conclusion

    Exam Tip: Whenever you see a question about water's unique properties (like its high boiling point, surface tension, or solvent ability), always look for the keyword "Hydrogen Bonding" or "Polarity." These two concepts explain almost everything about water's behavior in chemistry!

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15. 15.

    When a substance is oxidized, it

    1. A.Loses electrons
    2. B.Gains oxygen atoms
    3. C.Gains electrons
    4. D.Loses protons (H+ ions)

    Show answer

    Answer: A. Loses electrons

    AI explanation

    1. Analyze the Question

    The question asks for the fundamental definition of oxidation in chemical reactions. In chemistry, oxidation is one half of a redox (reduction-oxidation) reaction, and it is defined by the movement of electrons.

    2. Explain the Concept

    To understand oxidation, we use the popular mnemonic OIL RIG:

    • Oxidation Is Loss (of electrons)
    • Reduction Is Gain (of electrons)

    While oxidation can also involve the gain of oxygen or the loss of hydrogen, the most comprehensive and modern definition used in chemistry (especially for JAMB/WASSCE) is based on electron transfer. When an atom, ion, or molecule loses electrons, its oxidation state increases, which is the hallmark of oxidation.

    3. Show the Solution

    • Option A (Loses electrons): This is the definition of oxidation. For example, when Sodium ($Na$) becomes a Sodium ion ($Na^+$), it loses one electron: $Na \rightarrow Na^+ + e^-$. This is an oxidation process.
    • Option B (Gains oxygen atoms): While this is an older definition of oxidation, it is not the most fundamental. Not all oxidation reactions involve oxygen (e.g., the reaction between Sodium and Chlorine).
    • Option C (Gains electrons): This is the definition of reduction, not oxidation.
    • Option D (Loses protons): Losing protons ($H^+$) is often associated with oxidation in organic chemistry (dehydrogenation), but it is not the universal definition for all chemical substances.

    Comparing these, Option A is the most accurate and universal definition of oxidation used in chemistry examinations.

    4. Identify the Answer

    The correct option is A.

    5. Exam Tip

    Always remember OIL RIG. If you are ever confused during the exam, look at the charge of the element. If the charge becomes more positive (e.g., from $0$ to $+2$), the substance has lost electrons and has been oxidized. If the charge becomes more negative (e.g., from $0$ to $-1$), it has gained electrons and has been reduced.

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16. 16.

    Which of the following is a common laboratory indicator for bases?

    1. A.Methyl orange
    2. B.Phenolphthalein
    3. C.Bromothymol blue
    4. D.Litmus

    Show answer

    Answer: B. Phenolphthalein

    AI explanation

    Analysis of the Question

    The question asks for a "common laboratory indicator for bases." While many indicators change color in both acidic and basic solutions, we are looking for the one most characteristically associated with identifying or titrating bases in a standard Nigerian secondary school laboratory setting.

    Concept Explanation

    An acid-base indicator is a substance that changes color depending on the pH of the solution it is added to.

    • Phenolphthalein is a weak organic acid. In acidic solutions, it is colorless. However, as the pH increases (becoming basic), it undergoes a structural change that turns it pink/magenta. Because its color change interval (pH 8.2 – 10.0) falls within the basic range, it is the standard choice for titrating strong bases against weak acids.

    Step-by-Step Solution

    1. Evaluate the options: • Methyl orange: Changes color in the acidic range (pH 3.1 – 4.4). It is typically used for titrating strong acids against weak bases. • Phenolphthalein: Changes color in the basic range (pH 8.2 – 10.0). It is the classic indicator for detecting the presence of a base or the endpoint of a base-related titration. • Bromothymol blue: Changes color near neutral pH (pH 6.0 – 7.6). It is often used for strong acid-strong base titrations. • Litmus: A general-purpose indicator that turns blue in bases and red in acids. While it works for bases, it is less precise for quantitative laboratory titrations compared to phenolphthalein.

    2. Conclusion: In the context of laboratory chemistry (especially for WASSCE/JAMB practicals), phenolphthalein is the most specific and commonly used indicator for identifying the presence of a base or determining the endpoint in a titration involving a base.

    Verification

    This aligns with standard chemistry curricula where phenolphthalein is taught as the primary indicator for basic solutions in titration experiments.

    Exam Tip

    Remember the "P-P" rule: Phenolphthalein is Pink in a base. If you are doing a titration and the solution turns pink, you have reached the basic endpoint!

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17. 17.

    What is the mass percentage of carbon (C) in methane (CH4)? (The molar mass of carbon is approximately 12 g/mol.)

    1. A.25%
    2. B.12%
    3. C.75%
    4. D.50%

    Show answer

    Answer: C. 75%

    AI explanation

    Analysis

    To find the mass percentage of an element in a compound, we need to compare the total mass of that specific element to the total molar mass of the entire compound, then multiply by 100.

    Concept

    The formula for mass percentage is:

    $\text{Mass \% of element} = \left( \frac{\text{Total mass of element in formula}}{\text{Molar mass of compound}} \right) \times 100\%$

    Step-by-Step Solution

    Step 1: Calculate the molar mass of Methane ($CH_4$)

    • Atomic mass of Carbon (C) = 12 g/mol
    • Atomic mass of Hydrogen (H) = 1 g/mol
    • Molar mass of $CH_4 = (1 \times 12) + (4 \times 1)$
    • Molar mass of $CH_4 = 12 + 4 = 16 \text{ g/mol}$

    Step 2: Identify the total mass of Carbon in the compound

    • There is only one atom of Carbon in $CH_4$.
    • Total mass of Carbon = $12 \text{ g/mol}$

    Step 3: Calculate the percentage

    • $\text{Mass \% of C} = \left( \frac{12}{16} \right) \times 100\%$
    • $\text{Mass \% of C} = 0.75 \times 100\%$
    • $\text{Mass \% of C} = 75\%$

    Conclusion

    The calculation shows that Carbon makes up 75% of the mass of a methane molecule.

    Exam Tip: When calculating mass percentages, always remember to count the number of atoms of the element present in the formula. For example, if the question asked for Hydrogen, you would use 4 (the mass of 4 H atoms) divided by 16, which would give you 25%.

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18. 18.

    Which of the following methods can be used to remove temporary hardness from water?

    1. A.Boiling
    2. B.Filtration
    3. C.sedimentation
    4. D.Chlorination

    Show answer

    Answer: A. Boiling

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19. 19.

    Which noble gas is radioactive and is produced as a decay product of uranium and thorium?

    1. A.Argon
    2. B.Krypton
    3. C.Radon
    4. D.Neon

    Show answer

    Answer: C. Radon

    AI explanation

    1. Analyze the Question

    The question asks for a specific noble gas that possesses two distinct characteristics:

    • It is radioactive.
    • It is formed as a result of the radioactive decay of heavier elements like uranium and thorium.

    2. Explain the Concept

    Noble gases (Group 18 elements) are generally known for being chemically inert (unreactive). However, they have different origins and properties:

    • Argon, Krypton, and Neon: These are stable, non-radioactive gases found in the atmosphere. They are obtained primarily through the fractional distillation of liquid air.
    • Radon: This is the heaviest noble gas. Unlike its group members, it is unstable and radioactive. It is a naturally occurring gas produced in the Earth's crust during the radioactive decay series of uranium-238 and thorium-232. Because it is a gas, it can seep out of soil and rocks into buildings, which is a significant environmental health concern.

    3. Show the Solution

    • Step 1: Evaluate the options based on radioactivity. Argon, Krypton, and Neon are stable isotopes and are not radioactive.
    • Step 2: Identify the decay process. The decay of Uranium ($^{238}\text{U}$) and Thorium ($^{232}\text{Th}$) involves the emission of alpha and beta particles, eventually leading to the formation of Radon ($^{222}\text{Rn}$ or $^{220}\text{Rn}$).
    • Step 3: Confirm the properties. Radon is the only noble gas that is radioactive and is a known byproduct of the decay chains of these heavy radioactive elements.

    4. Identify the Answer

    The correct option is C.

    5. Exam Tip

    To remember this for your JAMB exam, associate the word "Radon" with "Radiation." Since it is the only radioactive noble gas, the name itself serves as a hint. Also, remember that Radon is a health hazard in basements because it is a dense, radioactive gas that accumulates in poorly ventilated areas!

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20. 20.

    What is the maximum number of electrons that can occupy the second energy level (n=2)?

    1. A.2 electrons
    2. B.18 electrons
    3. C.8 electrons
    4. D.32 electrons

    Show answer

    Answer: C. 8 electrons

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21. 21.

    Which halogen is a gas at room temperature and is pale yellow in color?

    1. A.Chlorine (Cl)
    2. B.Fluorine (F)
    3. C.Iodine (I)
    4. D.Bromine (Br)

    Show answer

    Answer: B. Fluorine (F)

    AI explanation

    Analysis

    The question asks us to identify a specific halogen based on two physical properties: its state of matter at room temperature (gas) and its characteristic color (pale yellow).

    Concept Explanation

    The halogens are found in Group 7 of the Periodic Table. As you move down the group, the physical properties change systematically due to increasing molecular size and stronger Van der Waals forces. Here is a quick breakdown of their physical states and colors at room temperature:

    • Fluorine ($F_2$): A pale yellow gas.
    • Chlorine ($Cl_2$): A greenish-yellow gas.
    • Bromine ($Br_2$): A reddish-brown liquid.
    • Iodine ($I_2$): A dark grey/black solid (which sublimes into a purple vapor).

    Step-by-Step Solution

    1. Evaluate the state: We are looking for a gas. Fluorine and Chlorine are both gases at room temperature. Bromine is a liquid, and Iodine is a solid. This narrows our options to A and B.
    2. Evaluate the color: • Chlorine is described as greenish-yellow. • Fluorine is described as pale yellow.
    3. Conclusion: Comparing the description in the question ("pale yellow") with the properties of the halogens, Fluorine is the only one that fits the description perfectly.

    Correct Answer

    The correct option is B.

    Exam Tip

    To remember the colors of the halogens, use the mnemonic "F-C-B-I" and visualize the transition from light to dark:

    • Fluorine: Pale yellow (Lightest)
    • Chlorine: Greenish-yellow
    • Bromine: Reddish-brown
    • Iodine: Dark grey/purple (Darkest)

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22. 22.

    What is the molecular geometry of a molecule with three bonding pairs and no lone pairs around the central atom?

    1. A.Tetrahedral
    2. B.Trigonal planar
    3. C.Linear
    4. D.Octahedral

    Show answer

    Answer: B. Trigonal planar

    AI explanation

    Analysis

    The question asks for the molecular geometry of a central atom that has exactly three bonding pairs of electrons and zero lone pairs. This is a classic application of the Valence Shell Electron Pair Repulsion (VSEPR) theory.

    Concept Explanation

    The VSEPR theory states that electron pairs around a central atom arrange themselves as far apart as possible to minimize repulsion. The geometry is determined by the total number of electron domains (bonding pairs + lone pairs):

    • 2 bonding pairs, 0 lone pairs: Linear (180°)
    • 3 bonding pairs, 0 lone pairs: Trigonal planar (120°)
    • 4 bonding pairs, 0 lone pairs: Tetrahedral (109.5°)
    • 6 bonding pairs, 0 lone pairs: Octahedral (90°)

    When there are three bonding pairs and no lone pairs, the three bonds spread out in a flat, triangular shape to maximize the distance between them, resulting in a bond angle of 120°.

    Step-by-Step Solution

    1. Identify the electron domains: The problem specifies 3 bonding pairs and 0 lone pairs.
    2. Calculate total domains: $3 + 0 = 3$ total electron domains.
    3. Apply VSEPR rules: • For 3 domains, the most stable arrangement that minimizes repulsion is a flat triangle. • This geometry is known as Trigonal planar.
    4. Compare with options: • A (Tetrahedral) requires 4 bonding pairs. • B (Trigonal planar) matches our calculation of 3 bonding pairs. • C (Linear) requires 2 bonding pairs. • D (Octahedral) requires 6 bonding pairs.

    Conclusion

    The molecular geometry for a molecule with three bonding pairs and no lone pairs is Trigonal planar.

    Exam Tip: Remember the "3-3-3" rule for your exams: 3 electron pairs, 3 bonds, 3-sided shape (Trigonal planar). If you ever forget, just visualize a triangle—it has three sides and three corners!

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23. 23.

    What is the IUPAC name for the compound CCl$_4$?

    1. A.Tetrahydrochloride
    2. B.Tetrachloromethane
    3. C.Carbon tetrachloride
    4. D.Chloroform

    Show answer

    Answer: B. Tetrachloromethane

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24. 24.

    Which of the following statements is true regarding the melting and boiling points of pure substances?

    1. A.The boiling point is always higher than the melting point
    2. B.The melting point is always higher than the boiling point
    3. C.The melting and boiling points are always the same for all substances
    4. D.The melting and boiling points can vary depending on the substance

    Show answer

    Answer: D. The melting and boiling points can vary depending on the substance

    AI explanation

    Analysis

    The question asks us to identify the correct relationship between the melting and boiling points of pure substances. We need to evaluate the physical properties of matter and how these transition temperatures are defined for different substances.

    Concept Explanation

    • Melting Point: The specific temperature at which a solid substance changes into a liquid state.
    • Boiling Point: The specific temperature at which a liquid substance changes into a gaseous state.
    • Pure Substances: These have fixed, characteristic physical properties. However, these properties are unique to each specific substance. For example, the melting point of water ($0^\circ\text{C}$) is different from the melting point of iron ($1538^\circ\text{C}$).
    • Variation: Because different substances have different intermolecular forces (like hydrogen bonding, van der Waals forces, or metallic bonding), their melting and boiling points vary significantly from one substance to another.

    Step-by-Step Solution

    1. Evaluate Option A & B: These suggest a universal rule (e.g., "always higher"). Since melting points and boiling points depend on the nature of the substance, there is no universal rule that one must be higher than the other across all matter.
    2. Evaluate Option C: This is incorrect because if melting and boiling points were the same for all substances, all matter would exist in the same state at room temperature, which we know is false.
    3. Evaluate Option D: This statement acknowledges that these points are specific to the identity of the substance. Since different substances have different molecular structures and bond strengths, their melting and boiling points vary. This is a scientifically accurate observation.

    Conclusion

    The melting and boiling points are characteristic physical properties that differ from one substance to another. Therefore, they vary depending on the substance being examined.

    Exam Tip: When you see "always" or "never" in multiple-choice questions, be very careful. In chemistry, there are almost always exceptions to general rules, so statements using absolute terms are frequently incorrect.

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25. 25.

    When an acidic solution is diluted, what happens to its pH?

    1. A.It depends on the specific acid
    2. B.It decreases
    3. C.It remains the same
    4. D.It increases

    Show answer

    Answer: D. It increases

    AI explanation

    Analysis of the Question

    The question asks how the pH of an acidic solution changes when water is added to it (dilution). To answer this, we need to understand the relationship between pH, hydrogen ion concentration, and dilution.

    Concept Explanation

    1. Definition of pH: The pH of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration: $$\text{pH} = -\log_{10}[\text{H}^+]$$
    2. The Relationship: Because of the negative sign in the formula, there is an inverse relationship between pH and the concentration of hydrogen ions ($[\text{H}^+]$). • High $[\text{H}^+]$ = Low pH (more acidic) • Low $[\text{H}^+]$ = High pH (less acidic)
    3. Effect of Dilution: When you dilute an acidic solution by adding water, you are increasing the total volume of the solution. This causes the concentration of hydrogen ions ($[\text{H}^+]$) to decrease. As the concentration of hydrogen ions decreases, the solution becomes less acidic, causing the pH value to move closer to 7 (the neutral point).

    Step-by-Step Solution

    • Step 1: Identify the initial state. An acidic solution has a high concentration of $\text{H}^+$ ions, resulting in a low pH (typically below 7).
    • Step 2: Apply dilution. Adding water increases the volume, which spreads the existing $\text{H}^+$ ions over a larger space, thereby lowering their concentration.
    • Step 3: Observe the effect on pH. Since $[\text{H}^+]$ decreases, the value of $-\log_{10}[\text{H}^+]$ must increase.
    • Step 4: Conclusion. As the acid becomes more dilute, the pH value rises (e.g., a solution with pH 2 might move toward pH 3 or 4 upon dilution).

    Conclusion

    Exam Tip

    Remember the "pH Scale Rule": The pH scale is like a ladder. For acids, the "stronger" (more concentrated) the acid, the lower it is on the ladder (closer to 0). When you dilute an acid, you are moving it "up" the ladder toward 7, which means the pH value is increasing.

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26. 26.

    What is the main source of carbon monoxide (CO) in urban areas?

    1. A.Volcanic eruptions
    2. B.Vehicle emissions
    3. C.Forest fires
    4. D.Industrial processes

    Show answer

    Answer: B. Vehicle emissions

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27. 27.

    A blue litmus paper turns red when dipped into a solution. What does this indicate about the solution?

    1. A.The solution is basic
    2. B.The solution is neutral
    3. C.The solution is acidic
    4. D.The litmus paper is faulty

    Show answer

    Answer: C. The solution is acidic

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28. 28.

    Identify the reducing agent in the following reaction: Zn + CuSO$_4$ → ZnSO$_4$ + Cu

    1. A.Cu
    2. B.Zn
    3. C.ZnSO$_4$
    4. D.CuSO$_4$

    Show answer

    Answer: B. Zn

    AI explanation

    Analysis

    To identify the reducing agent, we need to analyze the changes in the oxidation states of the elements involved in the reaction. A reducing agent is the substance that gets oxidized (loses electrons) during a chemical reaction.

    Concept: Oxidation and Reduction (Redox)

    • Oxidation: The process of losing electrons, which results in an increase in oxidation state.
    • Reduction: The process of gaining electrons, which results in a decrease in oxidation state.
    • Reducing Agent: The substance that causes reduction by donating electrons; therefore, the reducing agent itself is oxidized.

    Step-by-Step Solution

    1. Assign oxidation states to each element: • Reactants: • Zn (elemental form) = 0 • CuSO$_4$: Cu is +2, SO$_4$ is -2. • Products: • ZnSO$_4$: Zn is +2, SO$_4$ is -2. • Cu (elemental form) = 0

    2. Track the changes: • Zinc (Zn): Oxidation state changes from 0 to +2. This is an increase in oxidation state, meaning Zn has lost electrons (Oxidation). • Copper (Cu): Oxidation state changes from +2 to 0. This is a decrease in oxidation state, meaning Cu has gained electrons (Reduction).

    3. Identify the roles: • Since Zn lost electrons and was oxidized, it acts as the reducing agent. • Since Cu$^{2+}$ gained electrons and was reduced, CuSO$_4$ acts as the oxidizing agent.

    Conclusion

    Because Zinc (Zn) is the substance that is oxidized, it is the reducing agent in this reaction.

    Exam Tip: Remember the mnemonic OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). If you find the substance that loses electrons, you have found the reducing agent!

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29. 29.

    Which of the following factors does NOT affect the rate of a chemical reaction?

    1. A.Concentration of reactants
    2. B.Presence of a catalyst
    3. C.Molecular weight of products
    4. D.Temperature

    Show answer

    Answer: C. Molecular weight of products

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30. 30.

    The process of rusting is an example of the formation of

    1. A.Basic oxide
    2. B.Acidic oxide
    3. C.Reducing oxide
    4. D.Amphoteric oxide

    Show answer

    Answer: A. Basic oxide

    AI explanation

    Analysis of the Question

    The question asks for the chemical classification of the product formed when iron undergoes the process of rusting.

    Concept Explanation

    Rusting is the corrosion of iron in the presence of oxygen and moisture. Chemically, iron reacts with oxygen to form hydrated iron(III) oxide, represented by the formula: $Fe_2O_3 \cdot xH_2O$

    To classify this oxide, we look at the nature of the metal involved. Iron is a transition metal. Generally:

    • Basic oxides are formed when metals react with oxygen (e.g., $Na_2O$, $MgO$, $Fe_2O_3$). They react with acids to form salt and water.
    • Acidic oxides are formed when non-metals react with oxygen (e.g., $CO_2$, $SO_2$).
    • Amphoteric oxides show both acidic and basic properties (e.g., $Al_2O_3$, $ZnO$).

    Since iron is a metal, its oxide ($Fe_2O_3$) acts as a base. It reacts with acids (like dilute $HCl$ or $H_2SO_4$) to produce iron salts and water, confirming its basic nature.

    Step-by-Step Solution

    1. Identify the reaction: Rusting is the oxidation of iron: $4Fe(s) + 3O_2(g) + xH_2O(l) \rightarrow 2Fe_2O_3 \cdot xH_2O(s)$.
    2. Determine the product: The primary component of rust is iron(III) oxide ($Fe_2O_3$).
    3. Classify the oxide: Iron(III) oxide is an oxide of a metal. Metal oxides are typically basic in nature because they react with acids to form salts.
    4. Conclusion: Therefore, the formation of rust is the formation of a basic oxide.

    Exam Tip

    Remember the "Metal-Base, Non-metal-Acid" rule:

    • Metal oxides = Basic (think MB - "My Brother").
    • Non-metal oxides = Acidic (think NA - "Not Available"). This simple mnemonic will help you classify almost any oxide you encounter in your JAMB Chemistry exam!

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31. 31.

    Which type of salt is found in antacid medications and is used to relieve heartburn and indigestion?

    1. A.Aluminum chloride
    2. B.Magnesium chloride
    3. C.Sodium chloride
    4. D.Calcium chloride

    Show answer

    Answer: A. Aluminum chloride

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32. 32.

    What is the principal ore of iron, from which iron is extracted?

    1. A.Calcite
    2. B.Bauxite
    3. C.Magnetite
    4. D.Hematite

    Show answer

    Answer: D. Hematite

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33. 33.

    Which transition metal is known for its multiple colorful oxidation states and compounds used in pigments and paints?

    1. A.Silver (Ag)
    2. B.Copper (Cu)
    3. C.Gold (Au)
    4. D.Zinc (Zn)

    Show answer

    Answer: B. Copper (Cu)

    AI explanation

    Analysis of the Question

    The question asks for a transition metal characterized by its ability to exhibit multiple oxidation states, which result in a variety of vibrant colors. These compounds are widely utilized in the manufacturing of pigments and paints.

    Concept Explanation

    Transition metals are defined by their ability to form stable ions with partially filled d-orbitals. This electronic structure allows them to:

    1. Exhibit variable oxidation states: Because the energy difference between the $ns$ and $(n-1)d$ orbitals is small, electrons can be lost easily in different combinations.
    2. Form colored compounds: When transition metal ions form complexes, the d-orbitals split into different energy levels. Electrons can absorb specific wavelengths of visible light to jump between these levels (d-d transitions), causing the compounds to appear colored.

    While many transition metals exhibit these properties, Copper (Cu) is historically and industrially famous for its distinct, vibrant colors (like the deep blue of copper(II) sulfate or the bright green of copper carbonates) used extensively in pigments, dyes, and paints.

    Step-by-Step Evaluation

    • A. Silver (Ag): Primarily exhibits a +1 oxidation state. Its compounds are mostly colorless or white, except for specific halides used in photography.
    • B. Copper (Cu): Exhibits +1 and +2 oxidation states. Its compounds are famously colorful (blues and greens) and have been used for centuries in pigments (e.g., Verdigris, Azurite).
    • C. Gold (Au): Primarily exhibits +1 and +3 states. While it forms colored compounds, it is not the primary metal associated with common industrial pigments compared to copper.
    • D. Zinc (Zn): While a d-block element, it is not a "true" transition metal because it has a full $d^{10}$ configuration in its common +2 state. Consequently, its compounds are typically white or colorless, not colorful.

    Conclusion

    Based on the chemical properties of transition metals and their industrial application in pigments, Copper is the most accurate answer.

    Exam Tip

    When you see questions about "colorful compounds" in transition metals, always look for elements like Copper (Cu), Iron (Fe), Chromium (Cr), or Manganese (Mn). If you see Zinc (Zn) or Scandium (Sc), remember they are often "exceptions" that do not form colored compounds because they lack partially filled d-orbitals in their common oxidation states!

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34. 34.

    Isotopes of an element have

    1. A.The same number of protons but different numbers of neutrons.
    2. B.The same number of neutrons and electrons
    3. C.The same number of protons and neutrons
    4. D.The same number of protons and electrons

    Show answer

    Answer: A. The same number of protons but different numbers of neutrons.

    AI explanation

    1. Analyze the question

    The question asks for the defining characteristic of isotopes. To answer this, we must recall the atomic structure of elements and how isotopes differ from one another.

    2. Explain the concept

    • Atomic Number (Z): This is the number of protons in the nucleus of an atom. It defines the identity of an element (e.g., all Carbon atoms have 6 protons).
    • Mass Number (A): This is the sum of protons and neutrons in the nucleus.
    • Isotopes: These are atoms of the same element that have the same atomic number (same number of protons) but different mass numbers (different number of neutrons).

    Because the number of protons is the same, the number of electrons in a neutral atom of an isotope remains the same as well. However, the variation in the number of neutrons is the primary reason why isotopes have different masses.

    3. Show the solution

    • Step 1: Identify the constant. Isotopes belong to the same element, so they must have the same number of protons.
    • Step 2: Identify the variable. Isotopes have different atomic masses, which is caused by a difference in the number of neutrons.
    • Step 3: Evaluate the options: • Option A: States they have the same protons but different neutrons. This matches our definition perfectly. • Option B: Incorrect, because if the number of neutrons were the same, they would not be isotopes. • Option C: Incorrect, because if both protons and neutrons were the same, the atoms would be identical, not isotopes. • Option D: While isotopes do have the same number of protons and electrons, this statement describes the property of atoms of the same element in general, but it fails to explain why they are isotopes (which specifically requires the mention of the difference in neutrons).

    4. Identify the answer

    The correct option is A.

    5. Exam Tip

    Think of isotopes as "siblings" in the periodic table: they share the same "family name" (the element identity/proton count), but they have different "weights" (neutron count). Always look for the option that mentions the difference in neutrons to identify isotopes correctly!

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35. 35.

    What happens to the value of the equilibrium constant (Kc) for a reaction if the reaction is reversed?

    1. A.It becomes zero
    2. B.It becomes negative
    3. C.It remains the same
    4. D.It becomes the reciprocal of the original value

    Show answer

    Answer: D. It becomes the reciprocal of the original value

    AI explanation

    Analysis

    The question asks how the equilibrium constant ($K_c$) of a chemical reaction changes when the direction of the reaction is reversed.

    Concept Explanation

    The equilibrium constant ($K_c$) is defined as the ratio of the concentration of products to the concentration of reactants, each raised to the power of their stoichiometric coefficients.

    For a general reversible reaction:

    $aA + bB \rightleftharpoons cC + dD$

    The equilibrium constant is:

    $K_c = \frac{[C]^c [D]^d}{[A]^a [B]^b}$

    When you reverse the reaction, the products become the reactants, and the reactants become the products:

    $cC + dD \rightleftharpoons aA + bB$

    The new equilibrium constant ($K_{c}'$) for this reversed reaction is:

    $K_{c}' = \frac{[A]^a [B]^b}{[C]^c [D]^d}$

    Step-by-Step Solution

    1. Compare the expression for the original reaction with the expression for the reversed reaction.
    2. You will notice that $K_{c}'$ is exactly the inverse (or reciprocal) of $K_c$.
    3. Mathematically, this is expressed as: $$K_{c}' = \frac{1}{K_c}$$
    4. Therefore, if the original constant was $K_c$, the new constant is $1/K_c$.

    Conclusion

    When a reaction is reversed, the new equilibrium constant is the reciprocal of the original equilibrium constant. This matches option D.

    Exam Tip: Remember that $K_c$ is temperature-dependent. If you change the temperature, the value of $K_c$ changes. However, changing the concentration, pressure, or adding a catalyst does not change the value of $K_c$. Reversing the reaction is the only way to mathematically invert the constant.

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36. 36.

    What is the solubility product constant (Ksp) used for?

    1. A.To measure the total mass of a solute that can dissolve in a solvent
    2. B.To determine the concentration of a solute in a saturated solution
    3. C.To calculate the solubility of a solute in a given solvent
    4. D.To compare the solubilities of different solutes in the same solvent

    Show answer

    Answer: C. To calculate the solubility of a solute in a given solvent

    AI explanation

    Analysis of the Question

    The question asks for the primary purpose or application of the Solubility Product Constant ($K_{sp}$) in chemistry. To answer this, we must understand what $K_{sp}$ represents in the context of chemical equilibrium.

    Concept Explanation

    The Solubility Product Constant ($K_{sp}$) is the equilibrium constant for the dissolution of a solid substance into an aqueous solution. It represents the product of the molar concentrations of the constituent ions, each raised to the power of its stoichiometric coefficient in the balanced chemical equation.

    • What it represents: It tells us how much of a sparingly soluble salt will dissolve in water at a specific temperature.
    • The Relationship: If you know the $K_{sp}$ value of a salt, you can mathematically derive the molar solubility (the number of moles of solute that can dissolve per liter of solution). Conversely, if you know the solubility, you can calculate the $K_{sp}$.

    Step-by-Step Breakdown

    1. Evaluate Option A: Solubility product is not about the "total mass" of a solute; it is specifically about the equilibrium concentrations of ions in a saturated solution.
    2. Evaluate Option B: While $K_{sp}$ relates to saturated solutions, it is a constant used to calculate or predict solubility, rather than just a measurement of concentration itself.
    3. Evaluate Option C: This is the most accurate description. The primary utility of $K_{sp}$ in analytical chemistry is to calculate the solubility of a sparingly soluble salt in a given solvent. By setting up an ICE (Initial, Change, Equilibrium) table and using the $K_{sp}$ expression, we can determine exactly how many moles per liter ($mol/dm^3$) of a substance will dissolve.
    4. Evaluate Option D: While $K_{sp}$ values can be used to compare solubilities, this is only true if the salts have the same stoichiometry (e.g., comparing two 1:1 salts). If the salts have different formulas (e.g., $AgCl$ vs $Ag_2CrO_4$), you cannot compare their solubilities just by looking at their $K_{sp}$ values. Therefore, Option C is the more fundamental and correct definition.

    Conclusion

    $K_{sp}$ is fundamentally a tool used to calculate the solubility of a solute in a solvent.

    Exam Tip

    When dealing with $K_{sp}$ questions in JAMB, always remember the "1:1 ratio" shortcut: For a salt like $AB$ that dissociates into $A^+$ and $B^-$, the $K_{sp} = s^2$ (where $s$ is solubility). For a salt like $AB_2$ that dissociates into $A^{2+}$ and $2B^-$, the $K_{sp} = 4s^3$. Knowing these relationships will save you time during the exam!

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37. 37.

    Which of the following metals is commonly alloyed with copper to make brass?

    1. A.Iron
    2. B.Nickel
    3. C.Aluminum
    4. D.Zinc

    Show answer

    Answer: D. Zinc

    AI explanation

    Analysis

    The question asks for the specific metal that, when combined with copper, forms the alloy known as brass.

    Concept Explanation

    An alloy is a homogeneous mixture of two or more elements, at least one of which is a metal. Alloys are created to improve the properties of pure metals, such as increasing hardness, preventing corrosion, or improving aesthetic appearance.

    • Brass is a well-known binary alloy consisting primarily of copper and zinc.
    • Bronze, by contrast, is an alloy of copper and tin.
    • Cupronickel is an alloy of copper and nickel.

    By understanding the composition of these common copper-based alloys, you can easily distinguish between them in exam scenarios.

    Step-by-Step Solution

    1. Identify the components of Brass: Brass is defined in chemistry as an alloy of copper (Cu) and zinc (Zn).
    2. Evaluate the options: • A. Iron: Copper and iron do not form brass. • B. Nickel: Copper and nickel form cupronickel. • C. Aluminum: Copper and aluminum form aluminum bronze. • D. Zinc: Copper and zinc form brass.
    3. Conclusion: Since brass is specifically defined as a copper-zinc alloy, option D is the correct component.

    Exam Tip

    To avoid mixing up these common alloys, use this simple mnemonic:

    • Brass = Cu + Zn (Think "Brass has a Zinc-y sound").
    • Bronze = Cu + Sn (Think "Bronze has a Tin-y sound").

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38. 38.

    An element has an atomic number of 8 and a mass number of 16. How many neutrons does this element have?

    1. A.24
    2. B.16
    3. C.8
    4. D.32

    Show answer

    Answer: C. 8

    AI explanation

    Analysis

    To find the number of neutrons in an atom, we need to understand the relationship between the atomic number, the mass number, and the subatomic particles (protons, neutrons, and electrons).

    Concept

    • Atomic Number ($Z$): This represents the number of protons in the nucleus of an atom. For a neutral atom, it is also equal to the number of electrons.
    • Mass Number ($A$): This is the sum of the number of protons and the number of neutrons in the nucleus.
    • Formula: $$\text{Mass Number} (A) = \text{Number of Protons} (Z) + \text{Number of Neutrons} (n)$$Therefore, to find the number of neutrons:$$\text{Neutrons} (n) = \text{Mass Number} (A) - \text{Atomic Number} (Z)$$

    Step-by-Step Solution

    1. Identify the given values: • Atomic Number ($Z$) = 8 • Mass Number ($A$) = 16
    2. Apply the formula: • $n = A - Z$ • $n = 16 - 8$
    3. Calculate the result: • $n = 8$

    The element described is Oxygen, which has 8 protons and 8 neutrons.

    Conclusion

    The number of neutrons is 8. Comparing this to your options: A. 24 B. 16 C. 8 D. 32

    The correct option is C.

    Exam Tip

    Always remember the acronym MAN: Mass number = Atomic number + Neutrons. If you are ever asked for neutrons, just subtract the smaller number (atomic number) from the larger number (mass number).

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39. 39.

    What is the main environmental concern associated with sulfur dioxide emissions?

    1. A.Formation of acid rain
    2. B.Global warming potential
    3. C.Depletion of the stratospheric ozone
    4. D.Depletion of the ozone layer

    Show answer

    Answer: A. Formation of acid rain

    AI explanation

    Analysis

    The question asks for the primary environmental impact caused by the release of sulfur dioxide ($SO_2$) into the atmosphere. This is a common topic in environmental chemistry, specifically regarding air pollution.

    Concept Explanation

    Sulfur dioxide ($SO_2$) is a gas primarily produced by the combustion of fossil fuels (like coal and oil) that contain sulfur impurities, as well as from volcanic activity and industrial processes.

    When $SO_2$ is released into the atmosphere, it reacts with water vapor, oxygen, and other chemicals to form sulfuric acid ($H_2SO_4$). This process is represented by the following chemical reactions:

    1. $2SO_2 + O_2 \rightarrow 2SO_3$
    2. $SO_3 + H_2O \rightarrow H_2SO_4$

    When this sulfuric acid dissolves in rainwater, it lowers the pH of the rain, making it acidic. This phenomenon is known as acid rain. Acid rain has harmful effects on the environment, including the acidification of lakes and streams, damage to forests, and the corrosion of buildings and statues made of limestone or marble.

    Step-by-Step Evaluation

    • Option A (Formation of acid rain): This is the direct and well-documented result of sulfur dioxide emissions. As explained above, $SO_2$ reacts with atmospheric moisture to form acidic precipitation.
    • Option B (Global warming potential): While some gases contribute to global warming (like $CO_2$ and $CH_4$), $SO_2$ is not a primary greenhouse gas. In fact, sulfate aerosols can have a slight cooling effect on the climate.
    • Option C & D (Depletion of the ozone layer): Ozone depletion is primarily caused by chlorofluorocarbons (CFCs) and other ozone-depleting substances, not by sulfur dioxide.

    Conclusion

    Based on the chemical properties of sulfur dioxide and its interaction with the atmosphere, the correct environmental concern is the formation of acid rain.

    Exam Tip: Whenever you see "Sulfur dioxide" or "Nitrogen oxides" in an environmental chemistry question, immediately associate them with acid rain. If you see "CFCs," associate them with ozone layer depletion.

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40. 40.

    Sodium reacts vigorously with water to produce

    1. A.Sodium chloride (NaCl) and oxygen gas (O2)
    2. B.Sodium nitrate (NaNO3) and water (H2O)
    3. C.Sodium hydroxide (NaOH) and hydrogen gas (H2)
    4. D.Sodium oxide (Na2O) and hydrogen gas (H2)

    Show answer

    Answer: C. Sodium hydroxide (NaOH) and hydrogen gas (H2)

    AI explanation

    Analysis

    The question asks for the products formed when a Group 1 metal (Sodium) reacts with water. This is a classic displacement reaction involving an alkali metal.

    Concept

    Group 1 metals (the alkali metals) are highly reactive. When they react with water, they displace hydrogen from the water molecule. The general equation for this reaction is: Metal + Water → Metal Hydroxide + Hydrogen Gas

    Because sodium is very reactive, this reaction is exothermic (releases heat), which is why it is described as "vigorous."

    Solution

    1. Identify the reactants: Sodium (Na) and Water ($H_2O$).
    2. Write the chemical equation: $2Na(s) + 2H_2O(l) \rightarrow 2NaOH(aq) + H_2(g)$
    3. Break down the products: • $NaOH$ (Sodium Hydroxide): This is an alkaline solution, which is why Group 1 metals are called "alkali metals." • $H_2$ (Hydrogen gas): This is released as a gas, often causing the sodium to fizz and move rapidly across the surface of the water.

    Comparing this to your options:

    • Option A is incorrect because chlorine is not present in the reactants.
    • Option B is incorrect because nitrogen is not present in the reactants.
    • Option C matches our chemical equation perfectly.
    • Option D is incorrect because the primary product in water is the hydroxide, not the oxide.

    Conclusion

    The reaction between sodium and water produces sodium hydroxide and hydrogen gas. This matches option C.

    Exam Tip

    Remember the acronym "MAHO" for Group 1 metals reacting with water: Metal + Aqua (water) → Hydroxide + Oxygen (wait, no—Hydrogen!). Just remember: Metal + Water → Hydroxide + Hydrogen. Also, always remember that alkali metals are stored in oil to prevent them from reacting with moisture in the air!

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41. 41.

    What is the sum of the oxidation numbers in a neutral compound?

    1. A.+2
    2. B.-1
    3. C.0
    4. D.+1

    Show answer

    Answer: C. 0

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