Which of the following can be obtained by fractional distillation?

B. Sodium Chloride from sea water

C. Iodine from solution of Iodine in carbon tetrachloride

D. Sulphur from the solution of sulphur in carbon disulphide

The best treatment for a student who accidentally poured conc tetraoxosulphate(vi) on his skin in the laboratory is to wash his skin with?

D. sodium trioxonitrate(v) solution

The products of the thermal decomposition of ammonium trioxonitrate(v) are?

A. Nitrogen (I) Oxide and Water

D. Nitrogen (IV) Oxide and Water

A few drop of conc HCL are added to about 10cm$^3$ of a solution of PH 3.4. The PH of the resulting mixture is?

D. the same as that of the pure water

To obtain pure carbon(ii)oxide from its mixture with carbon(iv)oxide, the mixture should be?

A. Passed over heated copper(ii)oxide

C. Bubbled through conc H$_2$SO$_4$

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JAMB 2020

2020 JAMB Chemistry Past Questions and Answers

The 2020 JAMB Chemistry past questions with answers: 40 objective questions from the 2020 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.
The chlorinated alkane often used industrially to remove grease is?
1. A.Tetrachloromethane
2. B.Chloromethane
3. C.Trichloromethane
4. D.Dichloromethane
Show answer
Answer: A. Tetrachloromethane
AI explanation
1. Analyze the Question
The question asks for a specific chlorinated alkane that is used in industrial settings as a degreasing agent (a solvent used to dissolve oils, fats, and greases).
2. Explain the Concept
In organic chemistry, chlorinated alkanes (also known as alkyl halides) are frequently used as solvents because they are non-polar. This allows them to dissolve other non-polar substances like grease and oil, which water cannot remove.
Tetrachloromethane ( $CCl_4$ ): Also known as carbon tetrachloride. It is a powerful solvent historically used in dry cleaning and industrial degreasing because it is highly effective at dissolving organic compounds.
Chloromethane ( $CH_3Cl$ ): A gas at room temperature, used primarily as a refrigerant or in chemical synthesis, not as a degreasing solvent.
Trichloromethane ( $CHCl_3$ ): Also known as chloroform. While it is a solvent, it is more commonly known for its historical use as an anesthetic and in laboratory synthesis.
Dichloromethane ( $CH_2Cl_2$ ): Also known as methylene chloride. It is a very common solvent, but in the context of standard chemistry curricula and historical industrial applications, Tetrachloromethane is the classic answer for heavy-duty industrial degreasing.
3. Show the Solution
Step 1: Identify the chemical properties required for a degreasing agent: it must be a non-polar solvent capable of dissolving lipids (fats/oils).
Step 2: Evaluate the options. Tetrachloromethane ( $CCl_4$ ) is a symmetrical, non-polar molecule with a high capacity to dissolve grease.
Step 3: Compare with industrial standards. Tetrachloromethane was the industry standard for dry cleaning and metal degreasing for many years before its use was restricted due to toxicity and environmental concerns (ozone depletion).
4. Identify the Answer
The correct option is A.
5. Exam Tip
When you see questions about "chlorinated solvents," remember that as the number of chlorine atoms increases in a methane molecule ( $CH_4 \rightarrow CH_3Cl \rightarrow CH_2Cl_2 \rightarrow CHCl_3 \rightarrow CCl_4$ ), the molecule becomes more non-polar and generally more effective as a solvent for non-polar substances like grease.
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2.
Which of the following can be obtained by fractional distillation?
1. A.Nitrogen from liquid air
2. B.Sodium Chloride from sea water
3. C.Iodine from solution of Iodine in carbon tetrachloride
4. D.Sulphur from the solution of sulphur in carbon disulphide
Show answer
Answer: A. Nitrogen from liquid air
AI explanation
Analysis
The question asks us to identify which of the provided processes utilizes fractional distillation as the primary method of separation. Fractional distillation is a technique used to separate a mixture of liquids that have different boiling points.
Concept Explanation
Fractional Distillation: This process involves heating a mixture and collecting the components (fractions) as they vaporize at different temperatures. It is most commonly used for separating miscible liquids, such as the components of crude oil or the gases in liquid air.
Liquid Air: Air is a mixture of gases (mainly nitrogen, oxygen, and argon). When air is liquefied under high pressure and low temperature, it becomes a mixture of liquids. Because these gases have different boiling points, they can be separated by fractional distillation.
Step-by-Step Solution
Evaluate Option A (Nitrogen from liquid air): Liquid air is a mixture of gases with different boiling points. Nitrogen has a boiling point of approximately -196°C, while oxygen boils at -183°C. Because their boiling points are distinct, fractional distillation is the standard industrial method used to separate them. This fits the definition perfectly.
Evaluate Option B (Sodium Chloride from sea water): This is typically achieved through evaporation or crystallization, not fractional distillation.
Evaluate Option C (Iodine from solution in carbon tetrachloride): This is a solid-liquid mixture. The separation is best achieved through solvent extraction or evaporation.
Evaluate Option D (Sulphur from solution in carbon disulphide): Similar to option C, this is a solid-liquid mixture. The sulphur is recovered by evaporation of the solvent (carbon disulphide).
Conclusion
Based on the principles of separation techniques, fractional distillation is specifically required for separating components of a liquid mixture with different boiling points, which is exactly how nitrogen is obtained from liquid air.
Exam Tip: Always remember the "Boiling Point Rule": If you see a question about separating liquids from a mixture (like crude oil or liquid air), the answer is almost always fractional distillation. If you are separating a solid dissolved in a liquid, look for evaporation or crystallization.
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3.
A gaseous metallic chloride MCl consists of 20.22% of M by mass. The formula of the chloride is? [ M = 27, Cl = 35.5]
1. A.MCl
2. B.MCl $_2$
3. C.MCl $_3$
4. D.M $_2$ Cl $_6$
Show answer
Answer: D. M $_2$ Cl $_6$
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4.
When cathode rays are deflected onto the electrode of an electrometer, the instrument becomes?
1. A.Bipolar
2. B.Negatively charged
3. C.Positively charged
4. D.Neutral
Show answer
Answer: B. Negatively charged
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5.
What mass of water is produced when 8.0g of hydrogen reacts with excess oxygen?
1. A.8.0g
2. B.16.0g
3. C.36.0g
4. D.72.0g
Show answer
Answer: D. 72.0g
AI explanation
1. Analyze the question
We are asked to calculate the mass of water ( $H_2O$ ) produced when 8.0g of hydrogen gas ( $H_2$ ) reacts completely with excess oxygen.
2. Explain the concept
To solve this, we use Stoichiometry. We must:
Write the balanced chemical equation for the reaction.
Determine the molar masses of the substances involved.
Use the mole ratio from the balanced equation to find the mass of the product.
The reaction between hydrogen and oxygen is:
$2H_2 + O_2 \rightarrow 2H_2O$
3. Show the solution
Step 1: Identify the molar masses.
Relative atomic mass of $H = 1.0$ , $O = 16.0$ .
Molar mass of $H_2 = 2 \times 1.0 = 2.0 \text{ g/mol}$ .
Molar mass of $H_2O = (2 \times 1.0) + 16.0 = 18.0 \text{ g/mol}$ .
Step 2: Use the balanced equation. From the equation $2H_2 + O_2 \rightarrow 2H_2O$ :
2 moles of $H_2$ produce 2 moles of $H_2O$ .
This means 1 mole of $H_2$ produces 1 mole of $H_2O$ .
Step 3: Calculate the moles of hydrogen used.
$\text{Moles} = \frac{\text{mass}}{\text{molar mass}}$
$\text{Moles of } H_2 = \frac{8.0 \text{ g}}{2.0 \text{ g/mol}} = 4.0 \text{ moles}$
Step 4: Calculate the mass of water produced. Since the ratio of $H_2$ to $H_2O$ is 1:1, 4.0 moles of $H_2$ will produce 4.0 moles of $H_2O$ .
$\text{Mass of } H_2O = \text{moles} \times \text{molar mass}$
$\text{Mass of } H_2O = 4.0 \text{ moles} \times 18.0 \text{ g/mol} = 72.0 \text{ g}$
4. Identify the answer
Comparing our result to the given options, the correct mass is 72.0g. This matches option D.
5. Tip
Always check that your chemical equation is balanced before starting your calculation. A common mistake is forgetting to account for the coefficients (the numbers in front of the molecules). In this case, the 2:2 ratio simplified to 1:1, but if you had missed the coefficients, your calculation would have been incorrect.
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6.
The best treatment for a student who accidentally poured conc tetraoxosulphate(vi) on his skin in the laboratory is to wash his skin with?
1. A.with cool running water
2. B.sodium hydroxide solution
3. C.iodine solution
4. D.sodium trioxonitrate(v) solution
Show answer
Answer: A. with cool running water
AI explanation
Analysis
This question tests your knowledge of laboratory safety protocols, specifically regarding the handling of chemical burns caused by strong acids like concentrated tetraoxosulphate(VI) acid ( $H_2SO_4$ ).
Concept
Concentrated tetraoxosulphate(VI) acid is a powerful dehydrating agent and a strong corrosive acid. When it comes into contact with the skin, it reacts exothermically (releasing a large amount of heat), which can cause severe thermal and chemical burns.
The primary goal in treating an acid spill on the skin is to dilute and remove the acid as quickly as possible. While it might seem logical to use a base (like sodium hydroxide) to "neutralize" the acid, this is highly dangerous. The reaction between a strong acid and a strong base is extremely exothermic; the heat generated by the neutralization reaction would cause even more severe burns to the skin.
Step-by-Step Solution
Immediate Action: The most effective way to stop the corrosive action of the acid is to flush the affected area with large volumes of cool, running water.
Dilution: Water dilutes the acid, lowering its concentration and washing it away from the skin surface.
Heat Dissipation: The "running" nature of the water helps to dissipate the heat generated by the initial contact, preventing further tissue damage.
Safety Protocol: In any laboratory setting (WASSCE/JAMB/NECO standards), the standard first-aid procedure for acid spills is to wash the area with plenty of water for at least 10–15 minutes before seeking medical attention.
Why other options are incorrect:
B (Sodium hydroxide): As mentioned, this is a strong base. Mixing it with the acid will cause a violent, heat-releasing reaction that will worsen the burn.
C (Iodine solution): This is an antiseptic and has no role in neutralizing or removing concentrated acids.
D (Sodium trioxonitrate(V)): This is a salt solution and does not help in neutralizing or safely removing the acid.
Exam Tip
Always remember the "Water First" rule for chemical spills. Never attempt to neutralize a strong acid or base spill on the skin with another chemical reagent; always use copious amounts of water to dilute and wash the substance away.
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7.
The products of the thermal decomposition of ammonium trioxonitrate(v) are?
1. A.Nitrogen (I) Oxide and Water
2. B.Ammonia and Oxide
3. C.Nitrogen and Water
4. D.Nitrogen (IV) Oxide and Water
Show answer
Answer: A. Nitrogen (I) Oxide and Water
AI explanation
Analysis
The question asks for the products formed when ammonium trioxonitrate(V)—commonly known as ammonium nitrate—undergoes thermal decomposition.
Concept
Thermal decomposition is the process where a single compound breaks down into two or more simpler substances when heated. Ammonium trioxonitrate(V) has the chemical formula $NH_4NO_3$ .
When heated gently, it undergoes a specific decomposition reaction where the nitrogen atoms in the ammonium ion and the nitrate ion combine to form dinitrogen monoxide (also known as nitrous oxide or nitrogen(I) oxide) and water vapor.
Solution
The balanced chemical equation for the thermal decomposition of ammonium trioxonitrate(V) is:
$NH_4NO_3(s) \xrightarrow{\Delta} N_2O(g) + 2H_2O(g)$
Reactant: Ammonium trioxonitrate(V) ( $NH_4NO_3$ ).
Products: • $N_2O$ is Nitrogen(I) oxide. • $2H_2O$ is Water (in the form of steam).
Comparing this to the provided options:
Option A: Nitrogen (I) Oxide and Water — Matches our equation.
Option B: Ammonia and Oxide — Incorrect.
Option C: Nitrogen and Water — Incorrect (this would occur if the reaction were different).
Option D: Nitrogen (IV) Oxide and Water — Incorrect (this is a common distractor).
Exam Tip
To avoid confusion in the exam hall, remember the "Ammonium Nitrate Rule":
Gentle heating: Produces $N_2O$ (Nitrogen(I) oxide) and $H_2O$ .
Strong/Explosive heating: Produces $N_2$ , $O_2$ , and $H_2O$ . Since the question implies standard thermal decomposition, always look for Nitrogen(I) oxide.
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8.
What are the possible oxidation numbers of an element if its atomic number is 17?
1. A.-1 and 7
2. B.-1 and 6
3. C.-3 and 5
4. D.-2 and 6
Show answer
Answer: A. -1 and 7
AI explanation
1. Analyze the Question
The question asks for the possible oxidation numbers of an element with an atomic number of 17. To solve this, we need to determine the electronic configuration of the element and understand how it gains or loses electrons to achieve a stable octet (a full outer shell).
2. Explain the Concept
Electronic Configuration: The atomic number (Z) of 17 corresponds to the element Chlorine (Cl).
Distribution: Filling the shells (2, 8, 7), we see that Chlorine has 7 electrons in its outermost shell (valence shell).
Octet Rule: Atoms generally react to achieve a stable configuration of 8 electrons in their outer shell. • Gaining electrons: Chlorine needs 1 more electron to complete its octet ( $7 + 1 = 8$ ). Gaining an electron results in an oxidation state of -1. • Losing/Sharing electrons: Because Chlorine is a non-metal with 7 valence electrons, it can also share or "lose" its valence electrons in covalent bonding with more electronegative elements (like Oxygen or Fluorine). The maximum positive oxidation state is equal to the number of valence electrons, which is +7.
3. Show the Solution
Step 1: Write the electronic configuration of the element (Z=17): $1s^2 2s^2 2p^6 3s^2 3p^5$ .
Step 2: Identify the valence electrons: There are $2 + 5 = 7$ electrons in the third shell.
Step 3: Determine the negative oxidation state: To complete the shell, it gains 1 electron. Oxidation state = -1.
Step 4: Determine the maximum positive oxidation state: It can involve all 7 valence electrons in bonding. Oxidation state = +7.
Combining these, the possible oxidation numbers for Chlorine are -1 and +7.
4. Identify the Answer
Comparing our result with the given options, we find that Option A matches our calculated values.
5. Exam Tip
For elements in Groups 15, 16, and 17, a quick trick to find the range of oxidation numbers is:
Negative state: (Group Number - 18)
Maximum positive state: (Group Number - 10) For Chlorine (Group 17):
Negative: $17 - 18 = -1$
Positive: $17 - 10 = +7$
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9.
The number of molecules of Carbon(iv)Oxide produced when 10.0g of CaCO $_3$ is treated with 0.2dm $^3$ of 1 Mole of HCL in the equation CaCO $_3$ + 2HCL ⇒ CaCl $_2$ + H $_2$ O + CO $_2$ , is?
1. A.1.00 X 10 $^{23}$
2. B.6.02 X 10 $^{23}$
3. C.6.02 X 10 $^{22}$
4. D.6.02 X 10 $^{24}$
Show answer
Answer: C. 6.02 X 10 $^{22}$
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10.
The general formula for the Alkanals is?
1. A.R $_2$ CO
2. B.RCHO
3. C.ROH
4. D.RCOOR
Show answer
Answer: B. RCHO
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11.
What process would coal undergo to give coal gas, coal tar, ammoniacal liquor and coke?
1. A.Steam distillation
2. B.Destructive distillation
3. C.Liquefication
4. D.Hydrolysis
Show answer
Answer: B. Destructive distillation
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12.
Chromatography is used to separate components of mixture which differ in their rates of ?
1. A.diffusion
2. B.migration
3. C.reaction
4. D.sedimentation
Show answer
Answer: B. migration
AI explanation
Analysis
The question asks for the fundamental principle behind chromatography. You need to identify the specific property that causes different components of a mixture to move at different speeds through a stationary phase when carried by a mobile phase.
Concept Explanation
Chromatography is a separation technique based on the principle of differential migration.
In chromatography, a mixture is dissolved in a fluid (the mobile phase), which carries it through a structure holding another material (the stationary phase). The components of the mixture travel at different rates because they have different affinities for the stationary phase versus the mobile phase:
Components that have a higher affinity for the mobile phase move faster.
Components that have a higher affinity for the stationary phase move slower.
Because they move at different speeds, they "migrate" through the system and separate over time.
Step-by-Step Solution
Evaluate Option A (Diffusion): Diffusion is the movement of particles from an area of high concentration to low concentration. While diffusion happens in chromatography, it is not the primary mechanism of separation.
Evaluate Option B (Migration): Migration refers to the movement of substances through a medium. In chromatography, the separation is specifically defined by the rate at which these substances migrate through the stationary phase. This is known as differential migration.
Evaluate Option C (Reaction): Chromatography is a physical separation technique, not a chemical reaction. The components do not change their chemical identity during the process.
Evaluate Option D (Sedimentation): Sedimentation is the process of settling particles out of a suspension, usually due to gravity or centrifugation. This is not the principle used in chromatography.
Since the components are separated based on how quickly they move (migrate) through the stationary phase, "migration" is the correct term.
Conclusion
Exam Tip: Whenever you see a question about chromatography, look for keywords like "adsorption," "partition," "stationary phase," "mobile phase," or "migration." These are the core concepts examiners test.
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13.
Four elements P, Q, R and S have atomic numbers of 4, 10, 12 and 14 respectively. Which of these elements is noble gas?
1. A.P
2. B.Q
3. C.R
4. D.S
Show answer
Answer: B. Q
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14.
Which of the following gases will rekindle a brightly splint?
1. A.NO $_2$
2. B.NO
3. C.N $_2$ O
4. D.CL $_2$
Show answer
Answer: C. N $_2$ O
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15.
The substance often used for vulcanization of rubber is?
1. A.Chlorine
2. B.Hydrogen peroxide
3. C.Sulphur
4. D.Tetraoxosulphate(vi) acid
Show answer
Answer: C. Sulphur
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16.
Liquid black soap is made by boiling palm oil with liquid extract of ash. The function of the ash is to provide the ?
1. A.Acid
2. B.Ester of alkanoic acid
3. C.Alkali
4. D.Alkanol
Show answer
Answer: C. Alkali
AI explanation
Analysis
The question asks for the chemical role of wood ash in the traditional process of making black soap (saponification).
Concept Explanation
The production of soap is a chemical process known as saponification. Saponification involves the reaction between a fat or oil (in this case, palm oil) and a strong base (an alkali).
Palm oil contains triglycerides (esters of glycerol and fatty acids).
Wood ash contains potassium carbonate ( $K_2CO_3$ ). When wood ash is mixed with water and filtered, the resulting extract is alkaline. This is because the potassium carbonate reacts with water to form potassium hydroxide ( $KOH$ ), which is a strong alkali.
When this alkaline extract is boiled with palm oil, the alkali breaks down the fat into glycerol and the potassium salt of the fatty acid (which is the soap).
Step-by-Step Solution
Identify the reactants: The process uses palm oil (the fat/oil source) and ash extract.
Determine the chemical nature of the ash extract: Ash extract is rich in potassium carbonate ( $K_2CO_3$ ), which creates an alkaline solution.
Apply the saponification principle: For soap to form, the oil must react with a base (alkali).
Conclusion: Since the ash extract provides the base necessary for the reaction to occur, its function is to provide the alkali.
Identification of the Answer
A. Acid: Incorrect. Acids do not react with oils to form soap.
B. Ester of alkanoic acid: Incorrect. This is what the palm oil itself contains; the ash does not provide this.
C. Alkali: Correct. The ash extract provides the potassium hydroxide/carbonate needed to saponify the oil.
D. Alkanol: Incorrect. Alkanol (glycerol) is a byproduct of the reaction, not the starting material provided by the ash.
Exam Tip
Remember the mnemonic "F.A.S.": Fat + Alkali = Soap. Whenever you see a question about soap production (saponification), always look for the option that mentions an alkali (like $NaOH$ or $KOH$ ) or a base!
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17.
A few drop of conc HCL are added to about 10cm $^3$ of a solution of PH 3.4. The PH of the resulting mixture is?
1. A.less than 3.4
2. B.greater than 3.4
3. C.unaltered
4. D.the same as that of the pure water
Show answer
Answer: A. less than 3.4
AI explanation
Analysis
The question asks how the pH of a solution changes when a strong acid (concentrated hydrochloric acid, HCl) is added to it.
Concept Explanation
pH Scale: The pH scale measures the acidity or alkalinity of a solution. It ranges from 0 to 14. • pH < 7 is acidic. • pH = 7 is neutral. • pH > 7 is alkaline (basic).
pH Definition: pH is defined as $-\log_{10}[H^+]$ , where $[H^+]$ is the concentration of hydrogen ions.
Relationship: As the concentration of hydrogen ions ( $H^+$ ) increases, the pH value decreases.
Effect of HCl: Concentrated HCl is a strong acid that dissociates completely in water to release a high concentration of $H^+$ ions. Adding this to any solution will significantly increase the total concentration of $H^+$ ions in that mixture.
Step-by-Step Solution
Initial State: The solution has a pH of 3.4, meaning it is already acidic.
Action: You are adding concentrated HCl, which is a source of many $H^+$ ions.
Reaction: The addition of $H^+$ ions increases the acidity of the solution.
Result: Since the concentration of $H^+$ ions has increased, the pH value must shift further away from 7 towards 0. Therefore, the new pH will be a value lower than 3.4 (e.g., it might drop to 2.0 or 1.5 depending on the amount added).
Conclusion
Because the addition of a strong acid increases the hydrogen ion concentration, the pH value will decrease. Comparing this to the options provided, the resulting pH must be less than 3.4.
Exam Tip: Always remember the "pH Seesaw": If the acidity ( $H^+$ concentration) goes up, the pH number goes down. If the alkalinity ( $OH^-$ concentration) goes up, the pH number goes up.
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18.
The most important element on the earth's crust is?
1. A.Nitrogen
2. B.Hydrogen
3. C.Oxygen
4. D.Fluorine
Show answer
Answer: C. Oxygen
AI explanation
1. Analyze the question
The question asks for the most abundant element found in the Earth's crust. It is important to distinguish between the Earth's crust (the outermost layer) and the Earth's atmosphere (where Nitrogen is most abundant).
2. Explain the concept
The Earth's crust is composed primarily of silicate minerals. These minerals are compounds formed by the combination of various elements with oxygen. Because oxygen is highly reactive and forms stable oxides with almost all common metals and metalloids (like silicon, aluminum, and iron), it makes up the largest percentage of the crust by mass.
Oxygen: Approximately 46.6% of the Earth's crust by mass.
Silicon: The second most abundant, at approximately 27.7%.
Aluminum: The third most abundant, at approximately 8.1%.
3. Show the solution
Nitrogen (A): This is the most abundant gas in the Earth's atmosphere (about 78%), not the crust.
Hydrogen (B): While abundant in the universe and in water, it is not the most abundant element in the solid Earth's crust.
Oxygen (C): Oxygen is the most abundant element in the Earth's crust because it is a major component of the rocks and minerals that make up the crust.
Fluorine (D): Fluorine is a halogen and is relatively rare in the Earth's crust compared to oxygen.
Comparing these, Oxygen holds the top position by a significant margin.
4. Identify the answer
The correct option is C.
5. Tip
To avoid confusion in the exam hall, remember this simple mnemonic: "O-Si-Al" (Oxygen, Silicon, Aluminum). These are the top three elements in the Earth's crust in descending order. Always read the question carefully to see if it asks for the crust or the atmosphere!
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19.
Deliquescent substances are also?
1. A.efflorescent
2. B.anhydrous
3. C.hygroscopic
4. D.insoluble
Show answer
Answer: C. hygroscopic
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20.
Which of the following types of bonding does not involve the formation of new substances?
1. A.Metallic
2. B.Covalent
3. C.Co-ordinate
4. D.Electrovalent
Show answer
Answer: A. Metallic
AI explanation
1. Analyze the question
The question asks us to identify which type of chemical bonding does not result in the formation of a new chemical substance (a compound). In chemistry, bonding usually involves the interaction of atoms to achieve stability, often leading to the creation of new compounds with properties different from the constituent elements.
2. Explain the concept
Covalent bonding: Involves the sharing of electrons between non-metal atoms to form molecules (new substances like $H_2O$ or $CO_2$ ).
Co-ordinate (Dative) bonding: A type of covalent bond where both electrons in the shared pair come from the same atom. This also results in the formation of new chemical species (e.g., the ammonium ion, $NH_4^+$ ).
Electrovalent (Ionic) bonding: Involves the complete transfer of electrons from a metal to a non-metal, resulting in the formation of ionic compounds (new substances like $NaCl$ ).
Metallic bonding: This is the force of attraction between "free-moving" valence electrons (the "sea of electrons") and the positively charged metal ions in a metallic lattice. Metallic bonding occurs between atoms of the same metal element. It does not create a new chemical compound; it simply holds the atoms of the metal together in its solid state.
3. Show the solution
When atoms of sodium ( $Na$ ) bond with chlorine ( $Cl$ ), they form sodium chloride ( $NaCl$ ), which is a new substance with properties totally different from the reactive metal and the poisonous gas. This is electrovalent bonding.
When hydrogen and oxygen atoms bond, they form water ( $H_2O$ ), a new substance. This is covalent bonding.
When copper atoms are bonded together in a piece of copper wire, they are held by metallic bonding. The copper remains copper; no new chemical substance is formed. The bonding is simply an internal force maintaining the structure of the element.
4. Identify the answer
Based on the analysis, metallic bonding is the only option listed that describes the interaction between atoms of the same element to maintain its structure, rather than a reaction creating a new chemical compound.
5. Tip
Think of Metallic bonding as a "community" of the same type of atoms holding hands, whereas Covalent, Co-ordinate, and Electrovalent bondings are "marriages" between different types of atoms that result in a "new family" (a new compound).
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21.
Helium is used in observation of ballons because it is?
1. A.Light and combustible
2. B.light and non-combustible
3. C.heavy and combustible
4. D.heavy and non-combustible
Show answer
Answer: B. light and non-combustible
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22.
Proteins in acid solution undergo?
1. A.Substitution
2. B.Fermentation
3. C.Hydrolysis
4. D.Polymerisation
Show answer
Answer: C. Hydrolysis
AI explanation
Analysis
The question asks for the chemical process that occurs when proteins are placed in an acidic solution. We need to identify the reaction that breaks down the complex protein structure into its simpler components (amino acids).
Concept Explanation
Proteins are large, complex molecules known as polymers. They are made up of long chains of smaller units called amino acids, which are linked together by peptide bonds.
In chemistry, hydrolysis is a reaction where a molecule is broken down by the addition of water. When proteins are heated in the presence of an acid (or a base, or specific enzymes), the peptide bonds holding the amino acids together are cleaved (broken) by the addition of water molecules. This process converts the protein back into its constituent amino acids.
Step-by-Step Solution
Identify the structure: Proteins are polypeptides (long chains of amino acids).
Identify the reagent: An acid solution provides the necessary environment (H⁺ ions) to catalyze the breaking of peptide bonds.
Analyze the reaction: • Substitution: Involves replacing one atom or group with another; this does not break down a polymer chain. • Fermentation: A metabolic process that converts sugar to acids, gases, or alcohol; it is not the primary reaction for protein breakdown in this context. • Hydrolysis: Specifically refers to the cleavage of chemical bonds by the addition of water. This is exactly what happens to proteins in an acidic medium. • Polymerisation: The process of joining small units (monomers) to form a large chain (polymer). This is the opposite of what happens here.
Conclusion: Since the acid facilitates the breaking of peptide bonds using water, the process is hydrolysis.
Final Answer
The correct option is C.
Exam Tip: Whenever you see "hydrolysis," think "breaking with water." Remember that proteins are broken down into amino acids via hydrolysis, while carbohydrates (like starch) are broken down into simple sugars (like glucose) via the same process.
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23.
8g of CH $_4$ occupies 11.2 at S.T.P. What volume would 22g of CH $_3$ CH $_2$ CH $_3$ occupy under the same condition?
1. A.3.7dm $^3$
2. B.11.2dm $^3$
3. C.22.4dm $^3$
4. D.33dm $^3$
Show answer
Answer: B. 11.2dm $^3$
AI explanation
1. Analyze the Question
We are given the mass and volume of Methane ( $CH_4$ ) at Standard Temperature and Pressure (S.T.P.). We need to find the volume that a specific mass of Propane ( $CH_3CH_2CH_3$ ) would occupy under the same conditions.
2. Explain the Concept
At S.T.P., the molar volume of any ideal gas is constant: 1 mole of any gas occupies 22.4 dm³. To solve this, we use the relationship:
$\text{Number of moles (n)} = \frac{\text{Mass (m)}}{\text{Molar Mass (M)}}$
Once we find the number of moles of the gas, we multiply by the molar volume (22.4 dm³/mol) to find the total volume.
3. Show the Solution
Step 1: Calculate the moles of Propane ( $C_3H_8$ )
Chemical formula for Propane: $CH_3CH_2CH_3$ is $C_3H_8$ .
Molar mass of $C_3H_8 = (3 \times 12) + (8 \times 1) = 36 + 8 = 44 \text{ g/mol}$ .
Given mass of Propane = $22 \text{ g}$ .
$\text{Moles of Propane} = \frac{\text{Mass}}{\text{Molar Mass}} = \frac{22}{44} = 0.5 \text{ moles}$ .
Step 2: Calculate the volume of Propane
Since 1 mole of any gas occupies 22.4 dm³ at S.T.P.:
$\text{Volume} = \text{Moles} \times 22.4 \text{ dm}^3/\text{mol}$
$\text{Volume} = 0.5 \times 22.4 = 11.2 \text{ dm}^3$ .
(Note: The information about $CH_4$ provided in the question is actually a distractor or a confirmation of the S.T.P. conditions, as 8g of $CH_4$ is 0.5 moles, which also occupies 11.2 dm³).
4. Identify the Answer
Comparing our result to the given options, the correct volume is 11.2 dm³.
5. Tip
Always remember the "Magic Number" 22.4! At S.T.P., if you know the number of moles of a gas, you simply multiply by 22.4 to get the volume in dm³. Don't get distracted by extra data—focus on the molar mass of the substance you are actually asked to calculate.
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24.
What quantity of electricity will liberate 0.125 mole of oxygen molecules during the electrolysis of dilute sodium chloride solution?
1. A.24,125 C
2. B.48,250 C
3. C.72,375 C
4. D.96,500 C
Show answer
Answer: B. 48,250 C
AI explanation
Analysis
To solve this problem, we need to understand the relationship between the amount of substance liberated during electrolysis and the quantity of electricity (charge) passed through the electrolyte. This is governed by Faraday’s Laws of Electrolysis.
Concept: Faraday’s Laws of Electrolysis
During the electrolysis of a dilute sodium chloride solution, the reaction at the anode involves the discharge of hydroxide ions ( $OH^-$ ) from water to produce oxygen gas ( $O_2$ ):
$4OH^-_{(aq)} \rightarrow 2H_2O_{(l)} + O_{2(g)} + 4e^-$
From this balanced equation, we can see that 4 moles of electrons are required to liberate 1 mole of oxygen gas.
The quantity of electricity ( $Q$ ) is related to the number of moles of electrons ( $n$ ) by the Faraday constant ( $F$ ), where $F \approx 96,500 \text{ C/mol}$ . The formula is:
$Q = n \times F$
Step-by-Step Solution
Determine the moles of electrons required: From the equation, 1 mole of $O_2$ requires 4 moles of electrons. Therefore, 0.125 moles of $O_2$ will require: $ $n = 0.125 \times 4$ $ $ $n = 0.5 \text{ moles of electrons}$ $
Calculate the quantity of electricity ( $Q$ ): Using the Faraday constant ( $F = 96,500 \text{ C/mol}$ ): $ $Q = 0.5 \text{ mol} \times 96,500 \text{ C/mol}$ $ $ $Q = 48,250 \text{ C}$ $
Conclusion
The quantity of electricity required to liberate 0.125 mole of oxygen molecules is 48,250 Coulombs. This matches option B.
Exam Tip
Always write out the half-equation for the gas being produced at the electrode. Remember that for oxygen ( $O_2$ ), it is a 4-electron process, whereas for hydrogen ( $H_2$ ), it is a 2-electron process. Knowing the stoichiometry of the half-equation is the key to solving any electrolysis calculation!
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25.
An example of a polysaccharide is?
1. A.Dextrose
2. B.Mannose
3. C.Glucose
4. D.Starch
Show answer
Answer: D. Starch
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26.
When water drops are added to calcium carbide in a container and the gas produced is passed through a jet and lighted, the resultant flame is called an?
1. A.Oxyethene
2. B.Oxyhydrocarbon flame
3. C.Oxyacetylene flame
4. D.Oxymethane flame
Show answer
Answer: C. Oxyacetylene flame
AI explanation
1. Analyze the question
The question asks for the name of the flame produced when the gas generated from the reaction between calcium carbide ( $CaC_2$ ) and water is ignited.
2. Explain the concept
The Reaction: When water is added to calcium carbide, a chemical reaction occurs that produces ethyne (also known as acetylene) gas and calcium hydroxide. • Equation: $CaC_2(s) + 2H_2O(l) \rightarrow C_2H_2(g) + Ca(OH)_2(aq)$
The Gas: The gas produced is $C_2H_2$ , which is ethyne (acetylene).
The Flame: When this gas is burned in the presence of oxygen (often through a specialized jet or torch), it produces an extremely hot flame. This specific type of flame is widely used in welding and cutting metals and is famously known as an oxyacetylene flame.
3. Show the solution
Step 1: Identify the gas produced: $CaC_2 + 2H_2O \rightarrow C_2H_2 + Ca(OH)_2$ . The gas is ethyne ( $C_2H_2$ ).
Step 2: Recognize the common name for ethyne: Ethyne is commonly referred to as acetylene.
Step 3: Combine the gas name with the oxygen source: Burning acetylene in oxygen creates the "oxyacetylene" flame.
Step 4: Compare with options: Option C matches this terminology perfectly.
4. Identify the answer
The correct option is C.
5. Exam Tip
In chemistry exams, remember that Ethyne = Acetylene. Whenever you see "calcium carbide" in a question, immediately associate it with the production of ethyne gas. Also, remember that the oxyacetylene flame is famous for its very high temperature, which is why it is the standard for industrial welding.
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27.
Which of the following substances is a mixture?
1. A.Granulated sugar
2. B.Seawater
3. C.Sodium chloride
4. D.Iron filling
Show answer
Answer: B. Seawater
AI explanation
Analysis
The question asks us to identify which of the listed substances is a mixture. In chemistry, a mixture consists of two or more substances that are physically combined but not chemically bonded. This means the components can be separated by physical means (like filtration, evaporation, or distillation).
Concept Explanation
Pure Substances: These have a fixed chemical composition and distinct properties. They include elements (like Iron) and compounds (like Sodium chloride and Sugar).
Mixtures: These have variable compositions. They can be homogeneous (uniform throughout, like saltwater) or heterogeneous (non-uniform). • Granulated sugar (Sucrose): This is a pure compound with the chemical formula $C_{12}H_{22}O_{11}$ . • Seawater: This is a solution containing water, dissolved salts (like sodium chloride, magnesium chloride), gases, and organic matter. Because it contains various substances physically mixed together, it is classified as a mixture. • Sodium chloride (Table salt): This is a pure ionic compound with the chemical formula $NaCl$ . • Iron filings: This is a pure element (Fe).
Step-by-Step Solution
Evaluate A (Granulated sugar): Sugar is a compound. It has a constant chemical formula and properties. It is not a mixture.
Evaluate B (Seawater): Seawater is a complex solution. It contains water ( $H_2O$ ) and various dissolved minerals. Since these components are not chemically bonded to each other, it fits the definition of a mixture.
Evaluate C (Sodium chloride): This is a chemical compound formed by the reaction of sodium and chlorine. It is a pure substance.
Evaluate D (Iron filings): Iron is an element found on the periodic table. It is a pure substance.
Conclusion
Based on the definitions above, seawater is the only substance on the list that is a physical combination of multiple components.
Exam Tip
When you see a question about mixtures, look for substances that are "solutions" or "natural occurrences." If it has a specific chemical formula (like $NaCl$ or $C_{12}H_{22}O_{11}$ ), it is a compound, not a mixture!
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28.
An electron can be added to a halogen atom to form a halide ion with?
1. A.8 valence electrons
2. B.7 valence electrons
3. C.2 valence electrons
4. D.3 valence electrons
Show answer
Answer: A. 8 valence electrons
AI explanation
Analysis
The question asks about the electronic configuration of a halide ion formed when an electron is added to a neutral halogen atom.
Concept Explanation
Halogens: These are elements in Group 7 (or Group 17) of the Periodic Table. They include Fluorine (F), Chlorine (Cl), Bromine (Br), and Iodine (I).
Valence Electrons: A neutral halogen atom has 7 valence electrons in its outermost shell. This makes them highly reactive because they are one electron short of a stable "octet" (a full outer shell of 8 electrons).
Ion Formation: To achieve stability, a halogen atom gains one electron from another atom to complete its outer shell. When it gains this electron, it becomes a negatively charged ion called a halide ion.
The Octet Rule: Atoms generally react to achieve a stable electron configuration, which for most elements is having 8 electrons in their outermost shell (like the noble gases).
Step-by-Step Solution
Identify the starting state: A neutral halogen atom has 7 valence electrons ( $ns^2 np^5$ ).
Identify the process: The atom gains 1 electron to become a halide ion ( $X^-$ ).
Calculate the final state: $7 \text{ (original valence electrons)} + 1 \text{ (gained electron)} = 8 \text{ valence electrons}$ .
Conclusion: The resulting halide ion now has a stable octet configuration, meaning it has 8 electrons in its outermost shell.
Identifying the Answer
Comparing our result to the given options:
A. 8 valence electrons (Matches our calculation)
B. 7 valence electrons (This is the neutral atom, not the ion)
C. 2 valence electrons (Incorrect)
D. 3 valence electrons (Incorrect)
Exam Tip
Remember the "Octet Rule": Almost all main-group elements (except Hydrogen, Helium, Lithium, and Beryllium) "want" to have 8 electrons in their outer shell to be stable. If you see a question about an ion forming to become stable, the answer is almost always 8!
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29.
When a solid substance disappears completely as a gas on heating, the substance is said to have undergone?
1. A.Sublimation
2. B.Crystallization
3. C.Distillation
4. D.Evaporation
Show answer
Answer: A. Sublimation
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30.
If the quantity of oxygen occupying 2.76L container at a pressure of 0.825 atm and 300k is reduced by one-half, what is the pressure exerted by the remaining gas?
1. A.1.650atm
2. B.0.825atm
3. C.0.413atm
4. D.0.275atm
Show answer
Answer: C. 0.413atm
AI explanation
Analysis
To solve this problem, we need to understand the relationship between the amount of gas (moles) and the pressure it exerts within a fixed volume and temperature. This is governed by the Ideal Gas Law.
Concept
The Ideal Gas Law is expressed as:
$PV = nRT$
Where:
P = Pressure
V = Volume
n = Number of moles (quantity of gas)
R = Universal gas constant
T = Temperature
In this scenario, the volume ( $V$ ), temperature ( $T$ ), and the gas constant ( $R$ ) remain constant. Therefore, the pressure ( $P$ ) is directly proportional to the number of moles ( $n$ ):
$P \propto n$
This means that if you change the quantity of gas ( $n$ ) while keeping $V$ and $T$ constant, the pressure will change by the same factor.
Solution
Identify the initial state: • Initial Pressure ( $P_1$ ) = 0.825 atm • Initial quantity ( $n_1$ ) = $n$
Identify the final state: • The quantity of gas is reduced by one-half: $n_2 = \frac{1}{2}n_1$ • Since $P \propto n$ , the new pressure ( $P_2$ ) will also be one-half of the initial pressure.
Calculate the new pressure: $ $P_2 = \frac{1}{2} \times P_1$ $ $ $P_2 = \frac{1}{2} \times 0.825 \text{ atm}$ $ $ $P_2 = 0.4125 \text{ atm}$ $
Rounding to three decimal places as seen in the options, we get 0.413 atm.
Conclusion
Comparing our result to the given options, the correct value is 0.413 atm.
Exam Tip
Whenever you see a gas law problem, identify which variables are changing and which are held constant. If $V$ and $T$ are constant, you don't need to perform complex calculations with the Ideal Gas Law; simply look at how the change in moles ( $n$ ) affects the pressure ( $P$ ) directly!
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31.
An organic compound that does not undergo a reaction with both hydrogen cyanide and hydroxylamine can be?
1. A.Alkene
2. B.Alkanal
3. C.Alkanone
4. D.Alkanoic Acid
Show answer
Answer: D. Alkanoic Acid
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32.
The electronic configuration of an element is 1S $^2$ 2S $^2$ 2P $^6$ 3S $^2$ 3P $^3$ . How many unpaired electrons are there in the element?
1. A.5
2. B.4
3. C.3
4. D.2
Show answer
Answer: C. 3
AI explanation
Analysis
The question asks us to determine the number of unpaired electrons in an element based on its electronic configuration: 1s² 2s² 2p⁶ 3s² 3p³.
Concept: Hund’s Rule of Maximum Multiplicity
To find the number of unpaired electrons, we look at the valence shell (the outermost shell). Electrons in fully filled orbitals are paired, while electrons in partially filled orbitals may be unpaired.
According to Hund’s Rule, when filling orbitals of the same energy (like the three p-orbitals), electrons occupy them singly first before pairing up.
Step-by-Step Solution
Identify the valence subshell: Looking at the configuration 1s² 2s² 2p⁶ 3s² 3p³, the outermost subshell is 3p.
Analyze the 3p subshell: The p-subshell consists of three orbitals: $p_x$ , $p_y$ , and $p_z$ . Each orbital can hold a maximum of 2 electrons.
Distribute the 3 electrons into the 3p orbitals: Following Hund’s Rule, we place one electron into each of the three p-orbitals: • $p_x$ : 1 electron • $p_y$ : 1 electron • $p_z$ : 1 electron
Count the unpaired electrons: Since each of the three p-orbitals contains exactly one electron, there are 3 unpaired electrons. The inner shells (1s², 2s², 2p⁶, 3s²) are all completely filled, meaning all electrons in those shells are paired.
Conclusion
The element (which is Phosphorus, atomic number 15) has 3 unpaired electrons in its 3p subshell.
Exam Tip
When asked for unpaired electrons, always write out the subshell boxes. For any p³ configuration, you will always have 3 unpaired electrons. For d⁵, you will have 5 unpaired electrons. This is a common JAMB pattern, so mastering the orbital box diagram will save you time!
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33.
Which of the gas laws does this graph illustrate?
1. A.Boyle
2. B.Charles
3. C.Gay-Lussac
4. D.Graham
Show answer
Answer: D. Graham
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34.
How many valence electrons are contained in the element $^{31}_{15}P$ ?
1. A.3
2. B.4
3. C.15
4. D.31
Show answer
Answer: D. 31
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35.
The shape of ammonia molecule is?
1. A.Trigonal planar
2. B.Octahedral
3. C.Square planar
4. D.Tetrahedral
Show answer
Answer: C. Square planar
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36.
The volume occupied by 1.58g of a gas at S.T.P is 500cm $^3$ . What is the relative molecular mass of the gas? [ G.M.V at S.T.P = 22.4dm $^{3}$ ]
1. A.28
2. B.32
3. C.44
4. D.71
Show answer
Answer: D. 71
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37.
Aluminum hydroxide is used in the dyeing industry as a?
1. A.Dye
2. B.Dispersant
3. C.Salt
4. D.Mordant
Show answer
Answer: D. Mordant
AI explanation
1. Analyze the question
The question asks for the specific industrial application of aluminum hydroxide ( $Al(OH)_3$ ) in the context of the dyeing industry. We need to identify its role in helping dyes adhere to fabrics.
2. Explain the concept
In the dyeing industry, many dyes do not have a natural affinity for certain types of fabrics (like cotton). To make the dye "stick" to the fabric and become wash-fast, a substance called a mordant is used.
A mordant acts as a binding agent. It forms a coordination complex with the dye and the fabric, effectively "locking" the dye molecules onto the fibers. Aluminum hydroxide is a classic example of a metallic hydroxide used for this purpose because it is insoluble and can form stable complexes with both the fabric and the dye.
3. Show the solution
Dye (Option A): This is the substance that provides the color itself, not the binding agent.
Dispersant (Option B): This is a substance added to a suspension to improve the separation of particles and prevent settling. While important in some chemical processes, it is not the primary role of aluminum hydroxide in dyeing.
Salt (Option C): While aluminum hydroxide is a compound, it is not classified as a "salt" in the context of its function in dyeing.
Mordant (Option D): As explained above, a mordant is a substance used to set dyes on fabrics by forming a coordination compound with the dye. Aluminum hydroxide is widely recognized in chemistry as a mordant.
4. Identify the answer
5. Tip
Think of a mordant as a "chemical glue." If you ever see a question about substances used to fix dyes to fabrics (like alum or aluminum hydroxide), immediately look for the word "mordant."
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38.
To obtain pure carbon(ii)oxide from its mixture with carbon(iv)oxide, the mixture should be?
1. A.Passed over heated copper(ii)oxide
2. B.Bubbled through water
3. C.Bubbled through conc H $_2$ SO $_4$
4. D.Bubbled through conc NAOH
Show answer
Answer: D. Bubbled through conc NAOH
AI explanation
Analysis
The question asks for a chemical method to separate Carbon(II) oxide ( $CO$ ) from a mixture containing Carbon(IV) oxide ( $CO_2$ ). The key is to identify a substance that will react with one gas but not the other.
Concept Explanation
Carbon(IV) oxide ( $CO_2$ ): This is an acidic oxide. It reacts readily with alkaline solutions (bases) to form carbonates and water.
Carbon(II) oxide ( $CO$ ): This is a neutral oxide. It does not react with bases like sodium hydroxide ( $NaOH$ ).
To separate the two, we need a "scrubber"—a substance that will absorb the $CO_2$ while allowing the $CO$ to pass through unaffected.
Step-by-Step Solution
Evaluate the options: • A (Heated Copper(II) oxide): $CO$ reacts with heated $CuO$ to form $CO_2$ and $Cu$ . This would convert your $CO$ into $CO_2$ , which is the opposite of what you want. • B (Water): $CO_2$ is slightly soluble in water to form carbonic acid, but this is not an efficient way to remove it completely from a gas mixture. • C (Conc. $H_2SO_4$ ): Concentrated sulfuric acid is a drying agent. It removes water vapor but does not react with $CO_2$ . • D (Conc. $NaOH$ ): Sodium hydroxide is a strong base. When the mixture is bubbled through it, the $CO_2$ reacts according to the following equation: $2NaOH_{(aq)} + CO_{2(g)} \rightarrow Na_2CO_{3(aq)} + H_2O_{(l)}$ The $CO_2$ is trapped in the solution as sodium carbonate, while the $CO$ gas passes through the solution unchanged.
Conclusion: Bubbling the mixture through concentrated $NaOH$ is the standard laboratory method for removing $CO_2$ impurities from $CO$ .
Correct Answer
The correct option is D.
Exam Tip
Whenever you see a question asking to remove an acidic gas (like $CO_2$ , $SO_2$ , or $H_2S$ ) from a mixture, always look for an alkaline solution (like $NaOH$ or $KOH$ ) as your answer. They act as chemical "sponges" for acidic gases!
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39.
32g of anhydrous copper(ii)tetraoxosulphate(vi) dissolved in 1dm $^3$ of water generated 13.0kj of heat. The heat solution is?
1. A.26.0kj/mol
2. B.65.0kj/mol
3. C.130.0kj/mol
4. D.260.0kj/mol
Show answer
Answer: B. 65.0kj/mol
AI explanation
1. Analyze the Question
We are asked to calculate the molar heat of solution for anhydrous copper(II) tetraoxosulphate(VI) ( $CuSO_4$ ). We are given:
Mass of solute ( $m$ ) = 32g
Volume of solvent = 1 $dm^3$
Heat evolved ( $Q$ ) = 13.0 kJ
2. Explain the Concept
The molar heat of solution is the amount of heat energy absorbed or released when one mole of a substance is dissolved in a solvent. The formula is:
$\Delta H_{soln} = \frac{Q}{n}$
Where:
$Q$ is the heat change (in kJ).
$n$ is the number of moles of the solute.
To find $n$ , we use: $n = \frac{\text{mass}}{\text{molar mass}}$ .
3. Show the Solution
Step 1: Calculate the molar mass of $CuSO_4$ Using standard atomic masses: $Cu = 63.5$ , $S = 32$ , $O = 16$ .
Molar mass of $CuSO_4 = 63.5 + 32 + (4 \times 16)$
Molar mass of $CuSO_4 = 63.5 + 32 + 64 = 159.5 \text{ g/mol}$ (For simplicity in JAMB calculations, this is often approximated to 160 g/mol).
Step 2: Calculate the number of moles ( $n$ )
$n = \frac{32 \text{ g}}{160 \text{ g/mol}}$
$n = 0.2 \text{ moles}$
Step 3: Calculate the molar heat of solution
$\Delta H_{soln} = \frac{13.0 \text{ kJ}}{0.2 \text{ mol}}$
$\Delta H_{soln} = 65.0 \text{ kJ/mol}$
4. Identify the Answer
Comparing our result to the given options, the correct value is 65.0 kJ/mol.
Correct Option: B
5. Exam Tip
When dealing with molar heat calculations in JAMB, always remember to convert your mass to moles first. If you get a decimal like 0.2, dividing by it is the same as multiplying by 5 (since $1/0.2 = 5$ ). This is a quick mental math trick to save time during the exam!
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40.
Duralumin consists of aluminum, copper?
1. A.Zinc and Gold
2. B.Lead and Manganese
3. C.Nickel and Silver
4. D.Manganese and Magnesium
Show answer
Answer: D. Manganese and Magnesium
AI explanation
Analysis
The question asks for the composition of the alloy Duralumin. To answer this, we need to identify the specific metals that are combined with aluminum and copper to form this lightweight, high-strength alloy.
Concept
An alloy is a mixture of two or more elements, where at least one is a metal. Duralumin is a well-known alloy used extensively in the aircraft industry because it is strong, lightweight, and resistant to corrosion.
The standard composition of Duralumin is:
Aluminum (Al): Approximately 90–95% (the base metal)
Copper (Cu): Approximately 4%
Magnesium (Mg): Approximately 0.5–1%
Manganese (Mn): Approximately 0.5%
Step-by-Step Solution
Identify the base: We know Duralumin is an aluminum-based alloy.
Recall the additives: While aluminum and copper are the primary components, the specific properties of Duralumin (like its hardness and heat-treatability) are achieved by adding small amounts of Magnesium and Manganese.
Evaluate the options: • Option A (Zinc and Gold): Incorrect; these are not standard components of Duralumin. • Option B (Lead and Manganese): Incorrect; Lead is not a component. • Option C (Nickel and Silver): Incorrect; these are not components. • Option D (Manganese and Magnesium): Correct; these are the two essential trace elements added to the aluminum-copper base.
Conclusion
Based on the standard chemical composition of Duralumin, the correct components are Aluminum, Copper, Manganese, and Magnesium.
Exam Tip
To remember the composition of Duralumin, use the mnemonic "Dura-M&M":
Dura (Duralumin)
M (Manganese)
&
M (Magnesium) This helps you quickly associate the alloy with the two "M" metals!
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2020 JAMB Chemistry Past Questions and Answers

Questions

1. Analyze the Question

2. Explain the Concept

3. Show the Solution

4. Identify the Answer

5. Exam Tip

Analysis

Concept Explanation

Step-by-Step Solution

Conclusion

1. Analyze the question

2. Explain the concept

3. Show the solution

4. Identify the answer

5. Tip

Analysis

Concept

Step-by-Step Solution

Why other options are incorrect:

Exam Tip

Analysis

Concept

Solution

Exam Tip

1. Analyze the Question

2. Explain the Concept

3. Show the Solution

4. Identify the Answer

5. Exam Tip

Analysis

Concept Explanation

Step-by-Step Solution

Conclusion

Analysis

Concept Explanation

Step-by-Step Solution

Identification of the Answer

Exam Tip

Analysis

Concept Explanation

Step-by-Step Solution

Conclusion

1. Analyze the question

2. Explain the concept

3. Show the solution

4. Identify the answer

5. Tip

1. Analyze the question

2. Explain the concept

3. Show the solution

4. Identify the answer

5. Tip

Analysis

Concept Explanation

Step-by-Step Solution

Final Answer

1. Analyze the Question

2. Explain the Concept

3. Show the Solution

4. Identify the Answer

5. Tip

Analysis

Concept: Faraday’s Laws of Electrolysis

Step-by-Step Solution

Conclusion

Exam Tip

1. Analyze the question

2. Explain the concept

3. Show the solution

4. Identify the answer

5. Exam Tip

Analysis

Concept Explanation

Step-by-Step Solution

Conclusion

Exam Tip

Analysis

Concept Explanation

Step-by-Step Solution