Chemistry 2007 Jamb Examination
Question 11
Metals above hydrogen in the electrochemical series (e.g. Mg, Sn, Fe) react with dilute HCl, releasing H₂ gas.
Copper is below hydrogen and does not react. Correct option C.
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Question 12
Cl₂ + H₂O → HCl + HClO. Under bright sunlight, hypochlorous acid (HClO) decomposes to release O₂, leaving behind HCl.
Correct option A.
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Question 13
Since ΔH is negative, the forward reaction is exothermic. Increasing temperature shifts equilibrium in the endothermic (reverse) direction (Le Chatelier’s principle).
Correct option C.
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Question 14
Daniell’s cell involves Zn oxidized to Zn²⁺ and Cu²⁺ reduced to Cu(s). This is a redox reaction.
Correct option B.
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Question 15
Zinc displaces copper from CuSO₄ because it is more reactive: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s).
The blue Cu²⁺ colour fades as copper deposits. Correct option A.
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Question 16
C₂H₄(g) + H₂(g) → C₂H₆(g), ΔH = -137 kJ mol⁻¹. The reaction represented above is:
Since ΔH = -137 kJ mol⁻¹, heat is released during the hydrogenation of ethene, meaning it is exothermic.
Also,
Since ΔH has a negative value, it implies an exothermic reaction, which means a lot of heat is being liberated or evolved from the system to the environment.
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Question 17
Moles of Cu = 0.08/64 = 0.00125 mol.
Cu²⁺ + 2e⁻ → Cu. Electrons needed = 2 × 0.00125 = 0.0025 mol e⁻.
Charge = 0.0025 × 96500 = 241.25 C.
Time = Q/I = 241.25 / 0.5 = 482.5 s ≈ 8 min.
Correct option B.
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Question 18
Tartaric acid is added to sodium hydrogen carbonate to produce baking powder. It prevents the baking soda from leaving a bitter taste.
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Question 19
A strong acid + strong base gives a neutral salt, e.g. HCl + NaOH → NaCl + H₂O.
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Question 20
When NaOH dissolves, it dissociates into Na⁺ and OH⁻ ions. The disorder of the system increases, so entropy increases.
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In her analysis of Edith Wharton’s The House of Mirth (1905), scholar Candace Waid observes that the novel depicts the upper classes of New York society as “consumed by the appetite of a soulless ______ an apt assessment given that The House of Mirth is set during the Gilded Age, a period marked by rapid industrialization, economic greed, and widening wealth disparities. Which choice completes the text so that it conforms to the conventions of Standard English?