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JAMB 2023 · Part 2 of 2

2023 JAMB Chemistry Past Questions — Part 2

The 2023 JAMB Chemistry past questions with answers: 82 objective questions from the 2023 paper in the DeeepSolve question bank, each with its answer behind "Show answer". This is part 2 of 2: questions 42 to 82. Try each question before you check, then practise the paper as a timed JAMB-style CBT.

Past questions © the examination body (JAMB/WAEC/NECO). DeeepSolve is not affiliated with them. Rights holders: see /copyright.

Questions 42–82

  1. 42.

    Which trace gas in the atmosphere plays a significant role in the greenhouse effect?

    1. A.Oxygen
    2. B.Argon
    3. C.Carbon dioxide
    4. D.Nitrogen
    Show answer

    Answer: C. Carbon dioxide

    AI explanation

    Analysis

    The question asks for a trace gas in the atmosphere that contributes significantly to the greenhouse effect. To answer this, we must identify which of the listed gases has the ability to trap heat (infrared radiation) in the Earth's atmosphere.

    Concept Explanation

    The greenhouse effect is a natural process where certain gases in the atmosphere trap heat from the sun, keeping the Earth warm enough to support life. These are known as greenhouse gases.

    • Oxygen (O2O_2) and Nitrogen (N2N_2) make up the vast majority of our atmosphere (about 21% and 78% respectively). However, they are diatomic molecules with symmetrical bonds, meaning they do not absorb infrared radiation and therefore do not contribute to the greenhouse effect.
    • Argon (ArAr) is a noble gas. It is chemically inert and does not absorb infrared radiation.
    • Carbon dioxide (CO2CO_2) is a greenhouse gas. Even though it exists in relatively small concentrations (trace amounts) compared to nitrogen and oxygen, its molecular structure allows it to vibrate and absorb infrared radiation, effectively trapping heat in the atmosphere.
    Step-by-Step Solution
    1. Evaluate Oxygen and Nitrogen: These are the primary components of the atmosphere, but they are not greenhouse gases because they cannot absorb heat energy.
    2. Evaluate Argon: As a noble gas, it does not participate in the greenhouse effect.
    3. Evaluate Carbon dioxide: CO2CO_2 is well-documented as a primary greenhouse gas. Human activities, such as burning fossil fuels, have increased its concentration, leading to global warming.
    4. Conclusion: Among the options provided, only Carbon dioxide possesses the physical properties required to act as a greenhouse gas.
    Correct Answer

    The correct option is C.

    Exam Tip

    When you see questions about the greenhouse effect, remember the "Big Three" greenhouse gases: Carbon dioxide (CO2CO_2), Methane (CH4CH_4), and Water vapor (H2OH_2O). If you see any of these in an exam, they are almost certainly the intended answer! Also, never confuse "greenhouse gases" with "atmospheric composition"—Nitrogen and Oxygen are the most abundant gases, but they are not the ones responsible for global warming.

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  2. 43.

    What is the mass (in grams) of 500 mL of ethanol? (density of ethanol = 0.789 g/mL)

    1. A.394.5 mL
    2. B.500 mL
    3. C.394.5 g
    4. D.500 g
    Show answer

    Answer: C. 394.5 g

    AI explanation

    1. Analyze the question

    You are asked to calculate the mass of a substance (ethanol) given its volume and its density.

    • Volume (VV): 500 mL
    • Density (ρ\rho): 0.789 g/mL
    • Required: Mass (mm) in grams.
    2. Explain the concept

    In chemistry and physics, density is defined as the mass per unit volume of a substance. The relationship is expressed by the formula:

    Density(ρ)=Mass(m)Volume(V)\text{Density} (\rho) = \frac{\text{Mass} (m)}{\text{Volume} (V)}

    To find the mass, we rearrange the formula:

    Mass(m)=Density(ρ)×Volume(V)\text{Mass} (m) = \text{Density} (\rho) \times \text{Volume} (V)
    3. Show the solution

    Using the values provided:

    • ρ=0.789 g/mL\rho = 0.789 \text{ g/mL}
    • V=500 mLV = 500 \text{ mL}

    Substitute these into the rearranged formula:

    Mass=0.789 g/mL×500 mL\text{Mass} = 0.789 \text{ g/mL} \times 500 \text{ mL}
    Mass=394.5 g\text{Mass} = 394.5 \text{ g}

    (Note: The unit "mL" cancels out, leaving the result in grams.)

    4. Identify the answer

    Comparing our result to the given options: A. 394.5 mL (Incorrect unit) B. 500 mL (Incorrect unit and value) C. 394.5 g (Correct value and unit) D. 500 g (Incorrect value)

    5. Tip

    Always check the units before selecting your final answer. In this question, options A and B are in milliliters (volume), while C and D are in grams (mass). Since the question asks for mass, you can immediately eliminate any options that do not end in grams (g). This is a quick way to narrow down your choices in JAMB exams!

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  3. 44.

    If gas A has a molar mass of 32 g/mol and gas B has a molar mass of 64 g/mol, what is the ratio of their diffusion rates?

    1. A.2:1
    2. B.1:2
    3. C.1:1
    4. D.1:4
    Show answer

    Answer: B. 1:2

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  4. 45.

    Who proposed the planetary model of the atom with electrons orbiting the nucleus?

    1. A.Erwin Schrödinger
    2. B.Ernest Rutherford
    3. C.Niels Bohr
    4. D.J.J. Thomson
    Show answer

    Answer: B. Ernest Rutherford

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  5. 46.

    What unit of temperature should be used when applying the ideal gas law?

    1. A.Fahrenheit (°F)
    2. B.Kelvin (K)
    3. C.Rankine (°R)
    4. D.Celsius (°C)
    Show answer

    Answer: B. Kelvin (K)

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  6. 47.

    What is the atomic number of aluminium?

    1. A.13
    2. B.26
    3. C.14
    4. D.12
    Show answer

    Answer: A. 13

    AI explanation

    Analysis

    The question asks for the atomic number of the element Aluminium (Al). The atomic number represents the number of protons found in the nucleus of an atom of that element.

    Concept

    In the Periodic Table of Elements, elements are arranged in increasing order of their atomic numbers. Aluminium is a metal found in Group 13 and Period 3. Its electronic configuration is 1s22s22p63s23p11s^2 2s^2 2p^6 3s^2 3p^1. By summing the electrons (or counting the protons), we can determine its position.

    Step-by-Step Solution
    1. Recall the Periodic Table: Aluminium is the 13th element in the periodic table.
    2. Verify the configuration: The total number of electrons in a neutral aluminium atom is 2+2+6+2+1=132 + 2 + 6 + 2 + 1 = 13.
    3. Relate to Atomic Number: Since the number of protons equals the number of electrons in a neutral atom, the atomic number is 13.
    4. Evaluate the options: • A: 13 (Correct) • B: 26 (This is the approximate mass number of Aluminium, not the atomic number) • C: 14 (This is the atomic number of Silicon) • D: 12 (This is the atomic number of Magnesium)
    Conclusion

    The atomic number of Aluminium is 13.

    Exam Tip

    To remember the atomic numbers of the first 20 elements, use the mnemonic: Happy Henry Likes Beer But Could Not Obtain Food Near Nasty Moguls Always Sipping Potable Soda Clearly Arriving Kindly Calming. (H=1, He=2, Li=3, Be=4, B=5, C=6, N=7, O=8, F=9, Ne=10, Na=11, Mg=12, Al=13, Si=14, P=15, S=16, Cl=17, Ar=18, K=19, Ca=20).

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  7. 48.

    Balance the following redox reaction: Fe2_2O3_3 + CO → Fe + CO2_2

    1. A.Fe2_2O3_3 + CO → 2Fe + 2CO2_2
    2. B.2Fe2_2O3_3 + 3CO → 4Fe + 3CO2_2
    3. C.Fe2_2O3_3 + 2CO → 2Fe + 2CO2_2
    4. D.Fe2_2O3_3 + 3CO → 2Fe + 3CO2_2
    Show answer

    Answer: D. Fe2_2O3_3 + 3CO → 2Fe + 3CO2_2

    AI explanation

    To balance this chemical equation, we need to ensure that the number of atoms of each element is the same on both the reactant side (left) and the product side (right).

    1. Analyze the unbalanced equation

    Fe2_2O3_3 + CO → Fe + CO2_2

    • Reactants: 2 Fe, 4 O (3 from Fe2_2O3_3 + 1 from CO), 1 C
    • Products: 1 Fe, 2 O (from CO2_2), 1 C
    2. Step-by-step balancing
    • Balance Iron (Fe): There are 2 Fe atoms on the left. To balance this, we place a coefficient of 2 before Fe on the right. • Equation: Fe2_2O3_3 + CO → 2Fe + CO2_2
    • Balance Carbon (C): There is 1 C on the left and 1 C on the right. Currently, they are balanced.
    • Balance Oxygen (O): • On the left, we have 3 (from Fe2_2O3_3) + 1 (from CO) = 4 oxygen atoms. • On the right, we have 2 (from CO2_2). • To get 3 oxygen atoms from CO2_2 to match the 3 in Fe2_2O3_3, we need to adjust the coefficients. Let's try placing a 3 before CO and a 3 before CO2_2: • Equation: Fe2_2O3_3 + 3CO → 2Fe + 3CO2_2
    3. Final Check
    • Fe: 2 on the left; 2 on the right. (Balanced)
    • C: 3 on the left; 3 on the right. (Balanced)
    • O: (3 + 3) = 6 on the left; (3 × 2) = 6 on the right. (Balanced)

    The equation is now perfectly balanced.

    4. Identify the answer

    Comparing our result to the given options, the correct balanced equation is Fe2_2O3_3 + 3CO → 2Fe + 3CO2_2. This matches option D.

    Exam Tip

    When balancing redox equations involving oxides, always balance the metal atoms first, then the carbon/non-metal atoms, and leave the oxygen atoms for last. If you find yourself stuck with an odd number of oxygens, try doubling your coefficients to clear the fraction!

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  8. 49.

    Which of the following statements is true for strong electrolytes?

    1. A.They do not conduct electricity in the molten state
    2. B.They completely dissociate into ions in solution
    3. C.They are non-polar substances
    4. D.They partially dissociate into ions in solution
    Show answer

    Answer: B. They completely dissociate into ions in solution

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  9. 50.

    What is the product of the electrolysis of aqueous sodium chloride (NaCl) using inert electrodes?

    1. A.Hydrogen gas at the cathode and chlorine gas at the anode
    2. B.Hydrogen gas at the cathode and oxygen gas at the anode
    3. C.Sodium metal at the cathode and chlorine gas at the anode
    4. D.Sodium metal at the cathode and oxygen gas at the anode
    Show answer

    Answer: A. Hydrogen gas at the cathode and chlorine gas at the anode

    AI explanation

    Analysis of the Question

    This question tests your understanding of electrolysis of aqueous solutions. When we electrolyze a solution, we must consider the competition between ions moving to the electrodes.

    Concept Explanation

    In an aqueous solution of sodium chloride (NaCl\text{NaCl}), the following ions are present:

    • From NaCl\text{NaCl}: Na+\text{Na}^+ and Cl−\text{Cl}^-
    • From water (H2O\text{H}_2\text{O}): H+\text{H}^+ and OH−\text{OH}^-

    At the Cathode (Negative Electrode): Both Na+\text{Na}^+ and H+\text{H}^+ ions are attracted to the cathode. According to the electrochemical series, hydrogen is lower than sodium. Therefore, H+\text{H}^+ ions are preferentially discharged over Na+\text{Na}^+ ions.

    • Reaction: 2H++2e−→H2(g)2\text{H}^+ + 2e^- \rightarrow \text{H}_2(g)

    At the Anode (Positive Electrode): Both Cl−\text{Cl}^- and OH−\text{OH}^- ions are attracted to the anode. In a concentrated aqueous solution of NaCl\text{NaCl} (brine), the concentration of Cl−\text{Cl}^- is very high, which allows the chloride ions to be discharged instead of the hydroxide ions.

    • Reaction: 2Cl−→Cl2(g)+2e−2\text{Cl}^- \rightarrow \text{Cl}_2(g) + 2e^-
    Step-by-Step Solution
    1. Identify the ions: The solution contains Na+\text{Na}^+, H+\text{H}^+, Cl−\text{Cl}^-, and OH−\text{OH}^-.
    2. Determine the cathode product: Since H+\text{H}^+ is lower in the electrochemical series than Na+\text{Na}^+, hydrogen gas (H2\text{H}_2) is produced at the cathode.
    3. Determine the anode product: Because the solution is aqueous sodium chloride, the high concentration of chloride ions leads to the discharge of chlorine gas (Cl2\text{Cl}_2) at the anode.
    4. Conclusion: The electrolysis results in hydrogen gas at the cathode and chlorine gas at the anode.
    Identifying the Answer

    Comparing our findings with the provided options:

    • Option A matches our conclusion perfectly.
    Exam Tip

    Remember the "Preferential Discharge" rule:

    • Cathode: The ion lower in the electrochemical series is discharged (usually Hydrogen over Group 1 or 2 metals).
    • Anode: If the solution is concentrated, the halide (like Cl−\text{Cl}^-) is discharged. If the solution is very dilute, oxygen gas (O2\text{O}_2) is usually produced from the OH−\text{OH}^- ions.

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  10. 51.

    Which of the following is a characteristic property of acids?

    1. A.Turn litmus paper blue
    2. B.Bitter taste
    3. C.pH value above 7
    4. D.React with metals to produce hydrogen gas
    Show answer

    Answer: D. React with metals to produce hydrogen gas

    AI explanation

    Analysis

    The question asks for a characteristic property of acids. To solve this, we need to recall the fundamental chemical properties that define acids in an aqueous solution.

    Concept Explanation

    Acids are substances that, when dissolved in water, produce hydrogen ions (H+H^+). Their common characteristics include:

    1. Taste: They have a sour taste (e.g., citric acid in lemons).
    2. Litmus Test: They turn blue litmus paper red.
    3. pH Scale: They have a pH value of less than 7.
    4. Reactivity: They react with reactive metals (like Zinc, Magnesium, or Iron) to produce a salt and hydrogen gas.
    5. Neutralization: They react with bases to form salt and water.
    Step-by-Step Evaluation
    • Option A: Incorrect. Acids turn blue litmus paper red. Turning litmus paper blue is a property of bases (alkalis).
    • Option B: Incorrect. A bitter taste is a characteristic property of bases.
    • Option C: Incorrect. A pH value above 7 indicates a basic (alkaline) solution. Acids have a pH below 7.
    • Option D: Correct. When an acid reacts with a metal (e.g., Zn+2HCl→ZnCl2+H2Zn + 2HCl \rightarrow ZnCl_2 + H_2), hydrogen gas is evolved. This is a classic chemical test for acids.
    Conclusion

    Based on the chemical properties of acids, the correct characteristic is their ability to react with metals to produce hydrogen gas.

    Exam Tip

    Remember the acronym "BAR": Bases turn litmus Alkaline (blue) and Red litmus turns blue. For acids, just remember they are the opposite: they turn blue litmus red and have a pH < 7. Also, always associate "Acids + Metals" with "Hydrogen gas" as it is a very common JAMB question!

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  11. 52.

    At 2.0 atm pressure, the volume of a gas is 4.0 L. If the pressure is reduced to 1.0 atm while keeping the temperature constant, what will be the new volume of the gas?

    1. A.2.0 L
    2. B.6.0 L
    3. C.8.0 L
    4. D.4.0 L
    Show answer

    Answer: C. 8.0 L

    AI explanation

    1. Analyze the question

    We are given the initial pressure (P1P_1) and initial volume (V1V_1) of a gas. We need to find the new volume (V2V_2) when the pressure is changed to a new value (P2P_2), while the temperature remains constant.

    2. Explain the concept

    This problem is governed by Boyle's Law. Boyle's Law states that for a fixed mass of gas at a constant temperature, the volume of the gas is inversely proportional to its pressure.

    The formula is:

    P1V1=P2V2P_1V_1 = P_2V_2

    Where:

    • P1P_1 = Initial pressure
    • V1V_1 = Initial volume
    • P2P_2 = Final pressure
    • V2V_2 = Final volume
    3. Show the solution

    Given data:

    • P1=2.0 atmP_1 = 2.0 \text{ atm}
    • V1=4.0 LV_1 = 4.0 \text{ L}
    • P2=1.0 atmP_2 = 1.0 \text{ atm}
    • V2=?V_2 = ?

    Step-by-step calculation: Substitute the values into the Boyle's Law equation:

    (2.0 atm)×(4.0 L)=(1.0 atm)×V2(2.0 \text{ atm}) \times (4.0 \text{ L}) = (1.0 \text{ atm}) \times V_2

    Multiply the left side:

    8.0=1.0×V28.0 = 1.0 \times V_2

    Solve for V2V_2:

    V2=8.01.0V_2 = \frac{8.0}{1.0}
    V2=8.0 LV_2 = 8.0 \text{ L}
    4. Identify the answer

    The new volume of the gas is 8.0 L. This matches option C.

    5. Tip

    Exam Strategy: Always check the relationship between the variables. Since pressure was reduced (from 2.0 to 1.0), the volume must increase (from 4.0 to 8.0) because they are inversely proportional. If your calculated volume is smaller than the initial volume when pressure decreases, you know you've made a calculation error!

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  12. 53.

    Chlorine gas is commonly used in the production of which of the following industrial compounds?

    1. A.Chlorofluorocarbons (CFCs)
    2. B.Methane
    3. C.Ammonia
    4. D.Ethanol
    Show answer

    Answer: A. Chlorofluorocarbons (CFCs)

    AI explanation

    Analysis of the Question

    The question asks for an industrial compound that requires chlorine gas as a raw material for its production. We need to evaluate each option based on industrial chemical processes.

    Explanation of Concepts
    • Chlorine Gas (Cl2Cl_2): A highly reactive halogen used extensively in the chemical industry for bleaching, water treatment, and the synthesis of organic and inorganic compounds.
    • Chlorofluorocarbons (CFCs): These are organic compounds that contain carbon, chlorine, and fluorine. They are produced by replacing the hydrogen atoms in hydrocarbons (like methane or ethane) with chlorine and fluorine atoms through a process called halogenation. Chlorine gas is a primary reagent in this process.
    • Methane (CH4CH_4): This is a naturally occurring hydrocarbon (the main component of natural gas). It is a raw material, not a product made from chlorine.
    • Ammonia (NH3NH_3): Produced industrially via the Haber Process, which involves the reaction of nitrogen gas (N2N_2) and hydrogen gas (H2H_2). Chlorine is not involved.
    • Ethanol (C2H5OHC_2H_5OH): Produced industrially by the hydration of ethene or the fermentation of sugars. Chlorine is not a reactant in these processes.
    Step-by-Step Solution
    1. Evaluate Option A: CFCs (e.g., CCl2F2CCl_2F_2) are synthesized by reacting hydrocarbons with chlorine and fluorine. Chlorine gas is essential for the chlorination step.
    2. Evaluate Option B: Methane is a starting material (a reactant), not a product of a process using chlorine.
    3. Evaluate Option C: Ammonia is synthesized from Nitrogen and Hydrogen. Chlorine is not part of the Haber process.
    4. Evaluate Option D: Ethanol is produced from ethene or glucose. Chlorine is not used in these production pathways.

    Since chlorine is a fundamental component in the synthesis of CFCs, Option A is the correct industrial application.

    Conclusion

    The production of Chlorofluorocarbons (CFCs) relies on the substitution of hydrogen atoms in alkanes with chlorine atoms, making chlorine gas a vital industrial input for this process.

    Exam Tip

    When you see questions about industrial chemistry, remember the "Haber-Contact-Solvay" trio:

    • Haber Process: Ammonia (NH3NH_3)
    • Contact Process: Sulfuric Acid (H2SO4H_2SO_4)
    • Solvay Process: Sodium Carbonate (Na2CO3Na_2CO_3) If the question asks about chlorine, look for keywords like "bleaching," "PVC," or "CFCs."

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  13. 54.

    Which of the following is a unique property of water compared to other liquids?

    1. A.It is a poor solvent
    2. B.It does not evaporate
    3. C.It expands when freezing
    4. D.It has a low heat capacity
    Show answer

    Answer: C. It expands when freezing

    AI explanation

    Analysis

    The question asks us to identify a property of water that makes it behave differently from most other liquids. In chemistry, we look for "anomalous" properties—behaviors that deviate from the expected trends of similar substances.

    Concept Explanation

    Most substances contract (become denser) when they transition from a liquid state to a solid state. Water, however, exhibits anomalous expansion.

    When water cools down toward its freezing point (0∘C0^\circ\text{C}), its molecules arrange themselves into a rigid, open hexagonal lattice structure due to hydrogen bonding. This structure takes up more space than the molecules did in the liquid state. Consequently, ice is less dense than liquid water, which is why ice floats on water.

    Let’s look at the other options:

    • A: Water is actually known as the "universal solvent" because it dissolves many substances, so this is incorrect.
    • B: Water evaporates readily (think of puddles drying up), so this is incorrect.
    • D: Water has a very high specific heat capacity, which is why it is used in cooling systems and helps regulate the Earth's temperature.
    Step-by-Step Solution
    1. Evaluate Option A: Water is a polar solvent, making it an excellent solvent for ionic and polar compounds.
    2. Evaluate Option B: Water molecules have enough kinetic energy at room temperature to escape the surface as vapor.
    3. Evaluate Option C: As water cools from 4∘C4^\circ\text{C} to 0∘C0^\circ\text{C}, the hydrogen bonds force the molecules into a lattice that occupies a larger volume. This expansion is unique compared to most liquids that shrink upon freezing.
    4. Evaluate Option D: Water has one of the highest specific heat capacities of any common liquid, allowing it to absorb a lot of heat with little temperature change.

    Comparing these, Option C is the only one that describes a unique, anomalous property of water.

    Conclusion

    Exam Tip: Remember the "4-degree rule": Water is densest at 4∘C4^\circ\text{C}. Below this temperature, it begins to expand as it turns to ice. This is why pipes can burst in cold climates—the water inside expands as it freezes, exerting pressure on the pipe walls!

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  14. 55.

    What is the chemical structure of soap and detergent molecules?

    1. A.Hydrophilic head and hydrophobic tail
    2. B.Hydrophilic head and hydrophilic tail
    3. C.Hydrophobic head and hydrophobic tail
    4. D.Hydrophilic tail and hydrophobic head
    Show answer

    Answer: A. Hydrophilic head and hydrophobic tail

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  15. 56.

    What happens to the position of equilibrium, if a reversible exothermic reaction is subjected to a decrease in temperature?

    1. A.The position of equilibrium shifts to the left
    2. B.The position of equilibrium shifts to the right.
    3. C.The position of equilibrium remains unchanged
    4. D.The reaction stops
    Show answer

    Answer: B. The position of equilibrium shifts to the right.

    AI explanation

    Analysis of the Question

    This question tests your understanding of Le Chatelier’s Principle, which states that if a dynamic equilibrium is disturbed by changing the conditions (such as temperature, pressure, or concentration), the position of equilibrium shifts to counteract the change.

    Concept Explanation

    For a reversible reaction, we look at how heat behaves:

    • Exothermic reactions: These reactions release heat. We can think of heat as a product of the reaction. • Equation: Reactants⇌Products+HeatReactants \rightleftharpoons Products + Heat
    • Le Chatelier’s Principle regarding Temperature: • If you increase the temperature, the system tries to absorb the extra heat by shifting in the endothermic direction (left). • If you decrease the temperature, the system tries to produce more heat to compensate for the loss. It does this by shifting in the exothermic direction (right).
    Step-by-Step Solution
    1. Identify the reaction type: The question specifies an exothermic reaction.
    2. Represent the heat: Since it is exothermic, heat is on the product side.
    3. Apply the change: We are decreasing the temperature (removing heat).
    4. Predict the shift: According to Le Chatelier’s Principle, the system will attempt to replace the heat that was removed. To produce more heat, the reaction must proceed in the forward direction.
    5. Conclusion: The forward direction is the "right" side of the chemical equation. Therefore, the equilibrium position shifts to the right to produce more heat.
    Identifying the Answer

    Based on the principle explained above, decreasing the temperature of an exothermic reaction favors the forward reaction, shifting the equilibrium to the right.

    Exam Tip

    Think of an exothermic reaction like a heater. If you turn the heater down (decrease temperature), the system "panics" and tries to work harder to produce more heat (shifts right). If it were an endothermic reaction, it would be the opposite!

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  16. 57.

    Which of the following methods is commonly used to remove suspended impurities from water?

    1. A.Fluoridation
    2. B.Chlorination
    3. C.Filtration
    4. D.Distillation
    Show answer

    Answer: C. Filtration

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  17. 58.

    What is the state of matter in which particles are widely spaced and move freely with high kinetic energy?

    1. A.Liquid
    2. B.Solid
    3. C.Plasma
    4. D.Gas
    Show answer

    Answer: D. Gas

    AI explanation

    Analysis

    The question asks us to identify a state of matter based on three specific physical characteristics:

    1. Particle spacing: The particles are "widely spaced."
    2. Movement: The particles move "freely."
    3. Energy: The particles possess "high kinetic energy."
    Concept Explanation

    To understand this, let's look at the kinetic theory of matter for the three common states:

    • Solids: Particles are packed closely together in a fixed, orderly arrangement. They only vibrate about fixed positions and have the lowest kinetic energy.
    • Liquids: Particles are close together but can slide past one another. They have more kinetic energy than solids but are still restricted by intermolecular forces.
    • Gases: Particles are far apart (widely spaced) with very weak intermolecular forces. They move randomly and rapidly in all directions, meaning they possess high kinetic energy.
    • Plasma: While plasma is a state of matter consisting of ionized gas, in the context of standard JAMB Chemistry questions, the description of "widely spaced particles moving freely" is the classic definition of the Gaseous state.
    Step-by-Step Solution
    1. Evaluate Option B (Solid): Incorrect. Particles are tightly packed and vibrate in fixed positions, not moving freely.
    2. Evaluate Option A (Liquid): Incorrect. Particles are close together and have moderate kinetic energy, not widely spaced.
    3. Evaluate Option D (Gas): Correct. In a gas, the intermolecular forces are negligible, allowing particles to be far apart and move at high speeds (high kinetic energy) in random directions.
    4. Evaluate Option C (Plasma): While plasma involves high energy, it is an ionized state. In the context of basic chemistry curricula, the description provided is the standard definition for a gas.
    Conclusion

    The state of matter characterized by widely spaced particles and high kinetic energy is the gaseous state.

    Exam Tip: Remember the "Kinetic Theory of Matter" mnemonic: Solid (Vibrate), Liquid (Slide), Gas (Fly). If the particles are "flying" around, they have high kinetic energy and are in the gaseous state.

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  18. 59.

    According to the kinetic theory of gases, the pressure exerted by a gas is due to

    1. A.The vibrations of gas particles.
    2. B.The weight of the gas particles
    3. C.The attractive forces between gas particles
    4. D.The collisions of gas particles with the container walls
    Show answer

    Answer: D. The collisions of gas particles with the container walls

    AI explanation

    Analysis of the Question

    The question asks for the fundamental cause of gas pressure based on the Kinetic Molecular Theory (KMT). To answer this, we must look at how gas particles behave according to the assumptions of this theory.

    Concept Explanation

    The Kinetic Molecular Theory describes gases as being composed of a large number of tiny particles (atoms or molecules) that are in constant, random, and rapid motion.

    Key principles of the KMT regarding pressure include:

    1. Constant Motion: Gas particles move in straight lines until they collide with each other or the walls of their container.
    2. Elastic Collisions: When these particles hit the walls of the container, they exert a force.
    3. Definition of Pressure: In physics and chemistry, pressure is defined as Force per unit area (P=F/AP = F/A).
    4. The Source of Force: Since the particles are constantly bombarding the inner surfaces of the container, the cumulative force of these millions of tiny collisions per second creates what we measure as gas pressure.
    Step-by-Step Solution
    • Evaluate Option A: Gas particles move translationally (they move from place to place); they do not just vibrate in a fixed position like particles in a solid.
    • Evaluate Option B: The weight of gas particles is negligible and does not contribute to the pressure exerted on the walls of a container.
    • Evaluate Option C: A fundamental assumption of the Kinetic Theory for an ideal gas is that there are no significant attractive or repulsive forces between gas particles.
    • Evaluate Option D: As established by the KMT, pressure is the result of the continuous bombardment (collisions) of gas particles against the walls of the container. Each collision exerts a tiny force, and the sum of these forces over the area of the container wall results in pressure.
    Conclusion
    Exam Tip

    Whenever you see a question about the "Kinetic Theory of Gases," remember the acronym "R-E-C":

    • Random motion.
    • Elastic collisions (no energy is lost).
    • Collisions with walls create pressure.

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  19. 60.

    Which of the following reactions would be expected to have the highest entropy change?

    1. A.Liquid → Gas
    2. B.Solid → Liquid
    3. C.Gas → Liquid
    4. D.Gas → Solid
    Show answer

    Answer: A. Liquid → Gas

    AI explanation

    Analysis

    The question asks us to identify the process that results in the highest positive entropy change (ΔS\Delta S). Entropy is a measure of the degree of disorder or randomness in a system.

    Concept Explanation
    • Entropy (ΔS\Delta S): In thermodynamics, entropy increases as a substance moves from a more ordered state to a more disordered state. • Solid: Particles are tightly packed in a fixed, orderly structure (lowest entropy). • Liquid: Particles are close together but can move past one another (higher entropy than solid). • Gas: Particles are far apart, moving randomly at high speeds (highest entropy).
    • Entropy Change (ΔS\Delta S): • A transition from a more ordered state to a less ordered state results in a positive ΔS\Delta S (increase in disorder). • A transition from a less ordered state to a more ordered state results in a negative ΔS\Delta S (decrease in disorder).
    Step-by-Step Solution
    1. Evaluate the options: • A. Liquid → Gas: The substance moves from a state of moderate disorder to a state of high disorder (a large increase in entropy). • B. Solid → Liquid: The substance moves from a state of low disorder to moderate disorder (an increase in entropy, but smaller than liquid to gas). • C. Gas → Liquid: The substance moves from high disorder to moderate disorder (a decrease in entropy). • D. Gas → Solid: The substance moves from high disorder to very low disorder (a large decrease in entropy).
    1. Compare the changes: • The transition from Liquid to Gas involves the greatest increase in particle freedom and randomness, as the intermolecular forces are almost entirely overcome. Therefore, this process has the largest positive entropy change.
    Conclusion

    Exam Tip: Always remember the "Order of Entropy": Gas > Liquid > Solid. If you are moving "up" this ladder (e.g., Solid to Gas), entropy is increasing (ΔS>0\Delta S > 0). If you are moving "down" the ladder (e.g., Gas to Solid), entropy is decreasing (ΔS<0\Delta S < 0).

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  20. 61.

    What is the empirical formula of a compound containing 40.00% carbon, 6.67% hydrogen, and 53.33% oxygen by mass?

    1. A.C4_4H8_8O4_4
    2. B.CH2_2O
    3. C.C2_2H4_4O2_2
    4. D.C3_3H6_6O3_3
    Show answer

    Answer: B. CH2_2O

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  21. 62.

    Which organic compound is responsible for the characteristic aroma of fruits?

    1. A.Alkane
    2. B.Alkyne
    3. C.Ester
    4. D.Amine
    Show answer

    Answer: C. Ester

    AI explanation

    1. Analyze the question

    The question asks for the specific class of organic compounds that gives fruits their distinct, pleasant, and characteristic smell (aroma).

    2. Explain the concept

    In organic chemistry, different functional groups give compounds unique physical and chemical properties.

    • Alkanes are generally odorless or have a faint "petrol-like" smell.
    • Alkynes are unsaturated hydrocarbons and do not typically have fruity aromas.
    • Esters are formed by the reaction between a carboxylic acid and an alcohol (esterification). They are well-known in chemistry for having sweet, pleasant, and fruity odors. Many synthetic flavorings and perfumes are actually esters.
    • Amines are derivatives of ammonia and are notorious for having strong, fishy, or unpleasant odors.
    3. Show the solution
    • Step 1: Identify the functional group responsible for the "fruity" smell.
    • Step 2: Recall the properties of esters. Esters have the general formula RCOOR′RCOOR'. They are widely used in the food industry to create artificial fruit flavors (e.g., isoamyl acetate smells like bananas, and ethyl butyrate smells like pineapples).
    • Step 3: Compare this with the other options. Since alkanes, alkynes, and amines do not possess the characteristic sweet, fruity scent associated with esters, we can confidently eliminate them.
    4. Identify the answer

    The correct option is C.

    5. Exam Tip

    Memory Trick: Think of the word "Ester" as sounding like "Easter"—a time when people often enjoy sweet treats and fruits. Also, remember the mnemonic: "Esters are sweet, Amines are fishy." This simple contrast will help you remember their odors during your exam!

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  22. 63.

    Which of the following is a primary constituent of crude oil?

    1. A.Pentane
    2. B.Ethanol
    3. C.Heptane
    4. D.Methane
    Show answer

    Answer: D. Methane

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  23. 64.

    Which group does calcium belong to in the periodic table?

    1. A.Alkaline earth metals
    2. B.Halogens
    3. C.Alkali metals
    4. D.Noble gases
    Show answer

    Answer: A. Alkaline earth metals

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  24. 65.

    What happens when alkanoic acids react with alcohols in the presence of an acid catalyst?

    1. A.Saponification
    2. B.Esterification
    3. C.Polymerization
    4. D.Hydrolysis
    Show answer

    Answer: B. Esterification

    AI explanation

    Analysis of the Question

    The question asks for the name of the chemical reaction that occurs when an alkanoic acid (carboxylic acid) reacts with an alkanol (alcohol) in the presence of an acid catalyst (usually concentrated tetraoxosulphate(VI) acid, H2SO4H_2SO_4).

    Concept Explanation

    This reaction is a classic organic synthesis process known as Esterification.

    In this reaction:

    1. The carboxylic acid (RCOOHRCOOH) and the alcohol (R′OHR'OH) undergo a condensation reaction.
    2. A molecule of water (H2OH_2O) is removed.
    3. The resulting product is an ester (RCOOR′RCOOR') and water.
    4. The acid catalyst acts as a dehydrating agent to remove the water produced, which helps shift the equilibrium to favor the formation of the ester.

    The general equation is:

    RCOOH+R′OH⇌H2SO4heatRCOOR′+H2ORCOOH + R'OH \xrightleftharpoons[H_2SO_4]{heat} RCOOR' + H_2O
    Step-by-Step Solution
    • Step 1: Identify the reactants. We have an alkanoic acid and an alcohol.
    • Step 2: Identify the process. When these two functional groups combine with the removal of water, the product formed is an ester.
    • Step 3: Evaluate the options: • A. Saponification: This is the reverse of esterification; it is the alkaline hydrolysis of an ester to produce soap and glycerol. • B. Esterification: This is the formation of an ester from an acid and an alcohol. • C. Polymerization: This is the process of joining many small monomer units to form a large polymer chain. • D. Hydrolysis: This is the breaking down of a compound by reaction with water.

    Since the reaction produces an ester, the process is correctly identified as Esterification.

    Conclusion

    The reaction between an alkanoic acid and an alcohol to form an ester is called esterification.

    Exam Tip

    Remember the suffix: -ification usually implies "making." So, Esterification is the "making of an ester." Also, remember that this reaction is reversible; if you add water to an ester in the presence of an acid or base, you get the acid and alcohol back (this is called hydrolysis).

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  25. 66.

    How many pi (π\pi) bonds are there in an alkene with six carbon atoms?

    1. A.1
    2. B.6
    3. C.5
    4. D.3
    Show answer

    Answer: A. 1

    AI explanation

    Analysis

    The question asks for the number of pi (π\pi) bonds in an alkene containing six carbon atoms. To solve this, we need to understand the definition of an alkene and the nature of the bonds present in its structure.

    Concept Explanation
    1. What is an alkene? An alkene is an unsaturated hydrocarbon that contains at least one carbon-carbon double bond (C=CC=C). The general formula for a simple alkene with one double bond is CnH2nC_nH_{2n}.
    2. Bonding in Alkenes: A double bond consists of two types of bonds: • One sigma (σ\sigma) bond: This is the stronger, primary bond formed by the head-on overlap of orbitals. • One pi (π\pi) bond: This is the weaker, secondary bond formed by the side-to-side overlap of p-orbitals.
    3. The Rule: In any molecule, the number of pi bonds is determined by the number of double or triple bonds present. A single double bond contains exactly one pi bond.
    Step-by-Step Solution
    • Step 1: Identify the structure of the alkene. An alkene with six carbon atoms (hexene) has the molecular formula C6H12C_6H_{12}.
    • Step 2: Determine the number of double bonds. Unless specified as a "diene" or "triene," a standard alkene is defined by the presence of a single double bond.
    • Step 3: Calculate the pi bonds. Since a single double bond contains exactly one pi bond, an alkene with one double bond will have exactly one pi bond, regardless of the number of carbon atoms in the chain.
    Conclusion

    Whether the chain has two carbons (ethene) or six carbons (hexene), as long as it is a simple alkene, there is only one double bond in the structure. Therefore, there is only one pi bond.

    Exam Tip: Always remember that in organic chemistry, a single bond is one σ\sigma bond, a double bond is one σ\sigma and one π\pi bond, and a triple bond is one σ\sigma and two π\pi bonds. Don't let the number of carbon atoms distract you—focus on the functional group (the double bond)!

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  26. 67.

    What is the chemical formula of rust, which is formed on the surface of iron in the presence of oxygen and moisture?

    1. A.Fe3_3O4_4
    2. B.FeO
    3. C.Fe(OH)3
    4. D.Fe2_2O3_3
    Show answer

    Answer: D. Fe2_2O3_3

    AI explanation

    1. Analyze the question

    The question asks for the chemical formula of "rust," the reddish-brown substance that forms on iron when it is exposed to oxygen and water (moisture).

    2. Explain the concept

    Rusting is a chemical process known as corrosion. It is an electrochemical reaction where iron reacts with oxygen and water to form a hydrated oxide.

    The chemical equation for the formation of rust is:

    4Fe(s)+3O2(g)+xH2O(l)→2Fe2O3⋅xH2O(s)4Fe(s) + 3O_2(g) + xH_2O(l) \rightarrow 2Fe_2O_3 \cdot xH_2O(s)

    In chemistry examinations, rust is primarily identified as hydrated iron(III) oxide. While the water content (xH2OxH_2O) varies, the core chemical compound representing the iron oxide component is iron(III) oxide, which has the formula Fe2_2O3_3.

    3. Show the solution
    • Fe3_3O4_4 (Option A): This is known as magnetite or iron(II, III) oxide. It is a black magnetic oxide, not the reddish-brown rust we see on iron.
    • FeO (Option B): This is iron(II) oxide, also known as wüstite. It is not the primary component of rust.
    • Fe(OH)3_3 (Option C): This is iron(III) hydroxide. While it can be a product in the intermediate stages of corrosion, it is not the standard chemical formula for rust.
    • Fe2_2O3_3 (Option D): This is iron(III) oxide. This is the correct chemical representation of the oxide layer formed during the rusting of iron.
    4. Identify the answer

    Comparing our analysis with the options provided, Fe2_2O3_3 is the correct chemical formula for rust.

    5. Tip

    To remember this easily, think of the "III" in iron(III) oxide. Iron has a valency of 3, and Oxygen has a valency of 2. By swapping the valencies (criss-cross method), you get Fe2_2O3_3.

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  27. 68.

    Which of the following is an example of a primary cell?

    1. A.Alkaline battery
    2. B.Nickel-cadmium battery
    3. C.Lead-acid battery
    4. D.Lithium-ion battery
    Show answer

    Answer: A. Alkaline battery

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  28. 69.

    Benzene can be converted to its derivative toluene by the addition of a methyl group. The reaction is an example of

    1. A.Nucleophilic substitution
    2. B.Elimination reaction
    3. C.Electrophilic substitution
    4. D.Addition reaction
    Show answer

    Answer: C. Electrophilic substitution

    AI explanation

    Analysis

    The question asks for the classification of the reaction where benzene is converted to toluene (methylbenzene) by adding a methyl group. This specific process is known as the Friedel-Crafts alkylation.

    Concept Explanation

    Benzene is an aromatic hydrocarbon characterized by a stable, delocalized pi-electron cloud. Because of this stability, benzene does not typically undergo addition reactions (which would break the aromatic ring). Instead, it undergoes electrophilic aromatic substitution.

    In the Friedel-Crafts alkylation:

    1. A methylating agent (like chloromethane, CH3ClCH_3Cl) reacts with a catalyst (like anhydrous AlCl3AlCl_3) to generate a strong electrophile: the methyl carbocation (CH3+CH_3^+).
    2. This electrophile is attracted to the electron-rich benzene ring.
    3. The electrophile attacks the ring, temporarily forming an intermediate, and then a hydrogen atom is displaced (substituted) from the benzene ring to restore aromaticity.
    Step-by-Step Solution
    1. Identify the Reactants: Benzene (C6H6C_6H_6) + Methylating agent (CH3ClCH_3Cl).
    2. Identify the Catalyst: Anhydrous Aluminum Chloride (AlCl3AlCl_3).
    3. The Mechanism: The CH3+CH_3^+ electrophile replaces one of the hydrogen atoms on the benzene ring.
    4. The Product: Toluene (C6H5CH3C_6H_5CH_3) + Hydrogen Chloride (HClHCl).
    5. Classification: Since a hydrogen atom on the benzene ring is replaced by a methyl group (CH3CH_3) and the aromatic ring structure is preserved, the reaction is a substitution reaction. Because the incoming group is an electrophile, it is specifically an electrophilic substitution.
    Conclusion

    Option A is incorrect because benzene is electron-rich and repels nucleophiles. Option B is incorrect because we are not removing atoms to form a double or triple bond. Option D is incorrect because addition would destroy the aromatic stability of the benzene ring.

    The correct classification is Electrophilic substitution.

    Exam Tip

    Whenever you see "Friedel-Crafts" (whether alkylation or acylation) in a Chemistry question, immediately associate it with Electrophilic Aromatic Substitution. Remember: Benzene loves to substitute, not add!

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  29. 70.

    What is eutrophication?

    1. A.The release of harmful chemicals into water bodies
    2. B.The excessive growth of algae due to nutrient enrichment
    3. C.The presence of heavy metals in water
    4. D.The formation of oil slicks on water surfaces
    Show answer

    Answer: B. The excessive growth of algae due to nutrient enrichment

    AI explanation

    1. Analyze the Question

    The question asks for the definition of eutrophication. This is a common topic in Chemistry (under Environmental Chemistry) and Biology, focusing on water pollution and the impact of human activities on aquatic ecosystems.

    2. Explain the Concept

    Eutrophication is a process that occurs when a body of water becomes overly enriched with minerals and nutrients, particularly nitrates and phosphates.

    • The Process: When fertilizers from farms or detergents from sewage runoff enter a water body, they act as "food" for aquatic plants.
    • The Result: This leads to a rapid, uncontrolled growth of algae (an "algal bloom").
    • The Consequence: As the algae die and decompose, bacteria consume the dissolved oxygen in the water. This creates an oxygen-depleted environment (hypoxia), which kills fish and other aquatic organisms, effectively destroying the ecosystem.
    3. Show the Solution
    • Option A: This describes general chemical pollution, which is too broad.
    • Option B: This accurately describes the biological result of nutrient enrichment (algal bloom), which is the definition of eutrophication.
    • Option C: This refers to heavy metal poisoning (like mercury or lead pollution), not eutrophication.
    • Option D: This refers to oil pollution, which blocks oxygen from entering the water but is not caused by nutrient enrichment.
    4. Identify the Answer

    The correct definition of eutrophication is the excessive growth of algae caused by an influx of nutrients. This matches Option B.

    5. Exam Tip

    To remember this for your JAMB exam, think of the word "Nutrient-rich". Eutrophication = Excessive Uncontrolled Thriving of algae due to Nutrients. If you see "nitrates" or "phosphates" in a question about water pollution, the answer is almost always related to eutrophication!

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  30. 71.

    Which of the following is an example of an endothermic reaction?

    1. A.Combustion of propane (C3_3H8_8) to produce carbon dioxide (CO2_2) and water (H2_2O).
    2. B.Burning of methane (CH4_4) in the presence of oxygen
    3. C.Formation of table salt (NaCl) from sodium (Na) and chlorine (Cl2_2).
    4. D.Decomposition of hydrogen peroxide (H2_2O2_2) into water (H2_2O) and oxygen (O2_2).
    Show answer

    Answer: B. Burning of methane (CH4_4) in the presence of oxygen

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  31. 72.

    The heat of reaction can be determined experimentally using a device called a

    1. A.Calorimeter
    2. B.Barometer
    3. C.Spectrometer
    4. D.Thermometer
    Show answer

    Answer: A. Calorimeter

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  32. 73.

    What is the trend for ionization energy across a period in the periodic table?

    1. A.Increases from left to right.
    2. B.Remains constant
    3. C.Varies randomly
    4. D.Decreases from left to right
    Show answer

    Answer: A. Increases from left to right.

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  33. 74.

    Which of the following is a common property of non-metals?

    1. A.Exist as solids at room temperature
    2. B.Tend to gain electrons in chemical reactions
    3. C.High thermal conductivity
    4. D.Readily form cations in chemical reactions
    Show answer

    Answer: B. Tend to gain electrons in chemical reactions

    AI explanation

    Analysis of the Question

    This question tests your understanding of the periodic trends and chemical behaviors of elements, specifically the fundamental differences between metals and non-metals.

    Concept Explanation

    To identify the correct property, let’s look at the nature of non-metals:

    • Electronic Configuration: Non-metals typically have 4 to 7 electrons in their outermost shell (valence shell). To achieve a stable octet (like noble gases), they need to gain electrons.
    • Electronegativity: Because they have high effective nuclear charges, they have a strong tendency to attract electrons toward themselves.
    • Metals vs. Non-metals: • Metals generally lose electrons to form cations (positively charged ions). • Non-metals generally gain electrons to form anions (negatively charged ions). • Physical Properties: Metals are generally good conductors of heat and electricity and are mostly solids (except Mercury). Non-metals are poor conductors and exist in various states (solids, liquids, or gases).
    Step-by-Step Evaluation of Options
    • Option A: Incorrect. While some non-metals are solids (like Carbon or Sulfur), many are gases (like Oxygen or Nitrogen) or liquids (like Bromine) at room temperature.
    • Option B: Correct. Because non-metals have high electronegativity and need to complete their valence shells, they readily gain electrons to form negative ions (anions).
    • Option C: Incorrect. Non-metals are generally poor conductors of heat and electricity (insulators).
    • Option D: Incorrect. Forming cations (positive ions) is a characteristic property of metals, which lose electrons easily.
    Conclusion

    Based on the chemical behavior of non-metals, they are characterized by their ability to gain electrons during chemical reactions to achieve stability.

    Exam Tip: Remember the mnemonic "OIL RIG": Oxidation Is Loss (of electrons, typical of metals), Reduction Is Gain (of electrons, typical of non-metals). Since non-metals gain electrons, they are the ones that undergo reduction in chemical reactions!

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  34. 75.

    Which functional group is present in alkanals?

    1. A.Carbonyl group (C=O)
    2. B.Hydroxyl group (-OH)
    3. C.Alkyl group (-R)
    4. D.Carboxyl group (-COOH)
    Show answer

    Answer: A. Carbonyl group (C=O)

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  35. 76.

    What is the valency of an element with the electronic configuration 2, 8, 7?

    1. A.7
    2. B.1
    3. C.2
    4. D.3
    Show answer

    Answer: B. 1

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  36. 77.

    The lanthanides and actinides are located in which block of the periodic table?

    1. A.P-block
    2. B.S-block
    3. C.F-block
    4. D.D-block
    Show answer

    Answer: C. F-block

    AI explanation

    Analysis

    The question asks for the specific block in the periodic table where the lanthanides (elements 57–71) and actinides (elements 89–103) are positioned.

    Concept Explanation

    In the periodic table, elements are categorized into blocks based on the orbital that the highest-energy electron occupies:

    • s-block: Groups 1 and 2 (alkali and alkaline earth metals).
    • p-block: Groups 13 to 18 (excluding helium).
    • d-block: Groups 3 to 12 (transition metals).
    • f-block: These are the two rows detached from the main body of the periodic table. They are called the inner transition metals.

    The lanthanides (also known as the lanthanoids) are filling the 4f subshell, while the actinides (also known as the actinoids) are filling the 5f subshell. Because their differentiating electrons enter the f-orbitals, they are collectively referred to as the f-block elements.

    Step-by-Step Solution
    1. Identify the groups: The main body of the periodic table contains the s, p, and d blocks.
    2. Locate the detached rows: At the bottom of the standard periodic table, you will see two rows of 14 elements each.
    3. Determine the orbital filling: These elements are characterized by the filling of the f-orbitals.
    4. Conclusion: Since the lanthanides and actinides are the only elements that have their valence electrons in the f-orbitals, they are classified as the f-block elements.
    Answer

    The correct option is C.

    Exam Tip

    Think of the periodic table as a building: the s and p blocks are the main floors, the d block is the basement (transition metals), and the f block is the "sub-basement" or the detached annex at the bottom. Remember: f stands for far down!

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  37. 78.

    At room temperature and standard pressure, chlorine gas is in which state of matter?

    1. A.Plasma
    2. B.Solid
    3. C.Liquid
    4. D.Gas
    Show answer

    Answer: D. Gas

    AI explanation

    Analysis

    The question asks for the physical state of chlorine (Cl2Cl_2) under standard laboratory conditions (room temperature and standard pressure).

    Concept Explanation

    To determine the state of matter of an element, we look at its position in the Periodic Table and its physical properties:

    • Chlorine is a halogen (Group 7 element).
    • Halogens exhibit a trend in their physical states as you move down the group: • Fluorine (F2F_2): Gas • Chlorine (Cl2Cl_2): Gas • Bromine (Br2Br_2): Liquid • Iodine (I2I_2): Solid
    • At room temperature (approximately 25°C) and standard pressure (1 atm), chlorine exists as a diatomic molecule (Cl2Cl_2). It is a pale yellow-green gas.
    Step-by-Step Solution
    1. Identify the substance: Chlorine is a non-metal found in Group 7 of the periodic table.
    2. Recall physical properties: Chlorine is well-known in chemistry as a reactive, toxic gas used for water purification and bleaching.
    3. Evaluate the options: • A (Plasma): This is an ionized state of matter, not applicable here. • B (Solid): Iodine is the solid halogen at room temperature. • C (Liquid): Bromine is the liquid halogen at room temperature. • D (Gas): Chlorine is a gas at room temperature.
    Conclusion

    Based on the physical properties of halogens, chlorine is a gas at room temperature and standard pressure.

    Exam Tip

    Remember the "Halogen State Trend": Gas, Gas, Liquid, Solid.

    • Fluorine & Chlorine = Gas
    • Bromine = Liquid
    • Iodine = Solid (Think: "GC-LS" to remember the order down the group!)

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  38. 79.

    The contact process is used for the industrial production of

    1. A.sulfuric acid (H2SO4)
    2. B.Hydrochloric acid (HCl)
    3. C.Sodium hydroxide (NaOH)
    4. D.Calcium oxide (CaO)
    Show answer

    Answer: A. sulfuric acid (H2SO4)

    AI explanation

    1. Analyze the question

    The question asks for the specific industrial process known as the "Contact process" and which chemical substance it is used to manufacture.

    2. Explain the concept

    In industrial chemistry, different processes are used to produce common chemicals on a large scale.

    • The Contact Process: This is the standard industrial method for producing sulfuric acid (H2SO4H_2SO_4). It involves the catalytic oxidation of sulfur dioxide (SO2SO_2) to sulfur trioxide (SO3SO_3), which is then absorbed in concentrated sulfuric acid to form oleum, followed by dilution with water.
    • Other processes for context: • Haber Process: Used for the production of Ammonia (NH3NH_3). • Solvay Process: Used for the production of Sodium carbonate (Na2CO3Na_2CO_3). • Downs Process: Used for the production of Sodium metal.
    3. Show the solution
    • Step 1: Identify the key stages of the Contact Process: • Burning sulfur in air to produce sulfur dioxide: S(s)+O2(g)→SO2(g)S(s) + O_2(g) \rightarrow SO_2(g) • Catalytic oxidation of sulfur dioxide: 2SO2(g)+O2(g)⇌2SO3(g)2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g) (using Vanadium(V) oxide as a catalyst). • Absorption of SO3SO_3 in concentrated H2SO4H_2SO_4 to form oleum (H2S2O7H_2S_2O_7). • Dilution of oleum to produce concentrated sulfuric acid.
    • Step 2: Compare this with the options provided. The process clearly leads to the production of sulfuric acid.
    4. Identify the answer

    The correct option is A.

    5. Exam Tip

    To avoid confusion in the exam hall, remember this mnemonic: "Contact for Acid, Haber for Ammonia." Also, always remember that the catalyst used in the Contact process is Vanadium(V) oxide (V2O5V_2O_5)—JAMB loves to ask about that catalyst!

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  39. 80.

    What is the molar mass of water (H2O)?

    1. A.18 g/mol
    2. B.22 g/mol
    3. C.16 g/mol
    4. D.12 g/mol
    Show answer

    Answer: A. 18 g/mol

    AI explanation

    Analysis

    To find the molar mass of a compound, we need to sum the atomic masses of all the individual atoms present in its chemical formula. The formula for water is H₂O.

    Concept

    The molar mass of a compound is calculated by:

    1. Identifying the number of atoms of each element in the formula.
    2. Multiplying the number of atoms by their respective relative atomic masses (found on the Periodic Table).
    3. Adding these values together.

    Key Atomic Masses:

    • Hydrogen (H) = 1 g/mol
    • Oxygen (O) = 16 g/mol
    Step-by-Step Solution
    1. Break down the formula: H₂O consists of 2 atoms of Hydrogen and 1 atom of Oxygen.
    2. Calculate the contribution of each element: • Hydrogen: 2 atoms×1 g/mol=2 g/mol2 \text{ atoms} \times 1 \text{ g/mol} = 2 \text{ g/mol} • Oxygen: 1 atom×16 g/mol=16 g/mol1 \text{ atom} \times 16 \text{ g/mol} = 16 \text{ g/mol}
    3. Sum the values: • Total Molar Mass = 2 g/mol+16 g/mol=18 g/mol2 \text{ g/mol} + 16 \text{ g/mol} = 18 \text{ g/mol}
    Conclusion
    Exam Tip

    Always keep a mental note of the atomic masses of the first 20 elements in the Periodic Table (H, He, Li, Be, B, C, N, O, F, Ne, etc.). Knowing these by heart will save you precious time during your JAMB exam, as you won't have to constantly flip to the periodic table provided in the booklet!

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  40. 81.

    Which of the following substances is NOT hygroscopic?

    1. A.Salt
    2. B.Sugar
    3. C.Silica gel
    4. D.Aluminum
    Show answer

    Answer: D. Aluminum

    AI explanation

    Analysis

    The question asks us to identify which of the listed substances is not hygroscopic. To answer this, we must first understand what "hygroscopic" means in chemistry.

    Concept: Hygroscopic Substances

    A hygroscopic substance is one that has the ability to attract and hold water molecules from the surrounding environment through either absorption or adsorption. When these substances are exposed to air, they absorb moisture, often becoming damp or even dissolving in the water they have absorbed (a process known as deliquescence).

    • Common examples: Silica gel (used in shoe boxes to keep them dry), concentrated sulfuric acid, and common salt (sodium chloride) which often becomes "clumpy" in humid weather due to moisture absorption.
    • Non-hygroscopic substances: These are materials that do not naturally attract or hold water from the atmosphere. They remain stable and dry under normal atmospheric conditions.
    Step-by-Step Evaluation
    1. Salt (Sodium Chloride): Common table salt is hygroscopic. If you leave it in an open container during the rainy season in Nigeria, it absorbs moisture from the air and becomes damp.
    2. Sugar (Sucrose): Sugar is also hygroscopic. It attracts moisture from the air, which is why sugar cubes or granulated sugar can become sticky or clump together in humid conditions.
    3. Silica gel: This is a classic example of a desiccant. It is highly hygroscopic and is specifically manufactured to absorb moisture to protect goods from humidity.
    4. Aluminum: Aluminum is a metal. Metals like aluminum form a thin, protective oxide layer on their surface when exposed to air, but they do not absorb water molecules into their structure. Aluminum is not hygroscopic; it remains dry and does not change its physical state due to atmospheric humidity.
    Conclusion

    Based on the chemical properties of these substances, Aluminum is the only one that does not absorb moisture from the atmosphere.

    Exam Tip: When you see questions about "hygroscopic" or "deliquescent" substances, think of things that get "wet" or "sticky" when left out in the open air (like salt or sugar). Metals like Aluminum or iron (unless rusting) generally do not behave this way.

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  41. 82.

    Which of the following alkanes has a straight-chain structure?

    1. A.Cyclopentane (C5H10)
    2. B.Isobutane (C4H10)
    3. C.2 - methyl propane (C4H10)
    4. D.Pentane (C5H12)
    Show answer

    Answer: D. Pentane (C5H12)

    AI explanation

    Analysis of the Question

    The question asks us to identify which of the listed hydrocarbons is a straight-chain alkane. An alkane is a saturated hydrocarbon with the general formula CnH2n+2C_nH_{2n+2}. A "straight-chain" structure means the carbon atoms are connected in a continuous, unbranched sequence.

    Concept Explanation
    1. General Formula: Alkanes follow the CnH2n+2C_nH_{2n+2} rule.
    2. Straight-chain vs. Branched-chain: • Straight-chain: Every carbon atom is connected to at most two other carbon atoms (except for the ends). • Branched-chain: At least one carbon atom is connected to three or four other carbon atoms (e.g., "iso-" compounds or "methyl-" substituted compounds). • Cyclic: Compounds like "cyclo-" have carbon atoms joined in a ring, which is not a straight chain.
    Step-by-Step Solution
    • Option A: Cyclopentane (C5H10C_5H_{10}) This is a cyclic alkane. The carbon atoms form a ring, not a straight chain. It also follows the formula CnH2nC_nH_{2n}, which is characteristic of cycloalkanes, not straight-chain alkanes.
    • Option B: Isobutane (C4H10C_4H_{10}) Isobutane is the common name for 2-methylpropane. The prefix "iso-" indicates a branched structure where a methyl group is attached to the second carbon of a propane chain.
    • Option C: 2-methylpropane (C4H10C_4H_{10}) As the name suggests, there is a methyl group (−CH3-CH_3) branching off the main propane chain. This is a branched-chain alkane.
    • Option D: Pentane (C5H12C_5H_{12}) Pentane consists of five carbon atoms linked in a continuous line: CH3−CH2−CH2−CH2−CH3CH_3-CH_2-CH_2-CH_2-CH_3. It follows the general formula CnH2n+2C_nH_{2n+2} (C5H2(5)+2=C5H12C_5H_{2(5)+2} = C_5H_{12}) and has no branches. Therefore, it is a straight-chain alkane.
    Conclusion

    Comparing the structures, only Pentane represents a continuous, unbranched chain of carbon atoms.

    Exam Tip

    When you see names with prefixes like "iso-", "neo-", or numbers like "2-methyl", you are almost certainly looking at a branched structure. Straight-chain alkanes are usually named simply as "n-alkane" (e.g., n-pentane) or just by the parent name (e.g., Pentane).

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