Chemistry 2005 Jamb Examination
Question 1
B. NaOH
NaOH is a strong base that completely ionizes in aqueous solution, producing a high concentration of OH- ions. Hence, it has the highest pH.
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Question 2
Which of the following ions require the largest quantity of electricity for discharge at an electrode?
D. 2.0 moles of Al3+
The electricity required depends on equivalents (moles × charge). Al3+: 2 × 3 = 6. This is the largest among the available options
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Question 3
C. Colourless
Phenolphthalein is colourless in acidic medium and turns pink in basic medium.
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Question 4
D. Negative
Rusting of iron is a spontaneous process. For spontaneous processes, the Gibbs free energy change ΞG is negative.
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Question 5
A. 2NO + O2 β 2NO2
Here, nitrogen increases from +2 in NO to +4 in NO2, showing an increase in oxidation number.
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Question 6
2Hβ + Oβ → 2HβO has ΔH = −571 kJ. How much heat is liberated if 12.0 g of hydrogen burns in excess oxygen?
D. −1713 kJ
From the thermochemical equation, −571 kJ corresponds to 2 mol of H2. Using M(H2) = 2 g mol−1:
\[n(\mathrm{H_2}) = \dfrac{12.0}{2} = 6~\text{mol}\]
Heat released scales with moles:
\[\dfrac{−571~\text{kJ}}{2~\text{mol}} \times 6~\text{mol} = −1713~\text{kJ}\]
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Question 7
A concentrated solution containing H+, Cu2+, OH− and Cl− was electrolyzed with platinum electrodes. Which ion is discharged at the cathode?
A. \(Cu^{2+}\)
At the cathode, reduction occurs. Between \(H^{+}\) and \(Cu^{2+}\), copper has a higher reduction potential and is preferentially discharged, depositing copper metal.
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Question 8
When sulphur(IV) oxide is bubbled into aqueous sodium hydroxide for a long time, the solution formed eventually is
C. NaHSO3
SO2 (acidic) reacts with NaOH to give sulfite in base excess and bisulfite when the gas is in excess or bubbled for long:
\[\mathrm{SO_2 + NaOH \rightarrow NaHSO_3}\] \[\mathrm{SO_2 + 2NaOH \rightarrow Na_2SO_3 + H_2O}\]
Prolonged passage of SO2 shifts the reaction toward the acid salt NaHSO3.
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Question 9
D. Dioxonitrate (III) ion
NO2β is nitrite. N oxidation state is +3; the anion has two O atoms β βdioxoβ¦(III)β.
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Question 10
What happens if an aluminium spoon is used to stir a solution of iron(II) trioxonitrate(V)?
A. The spoon is oxidized while Fe(II) is reduced to Fe(s)
Al is more electropositive and displaces Fe from Fe2+:
Aluminium is oxidized to Al3+, Fe2+ is reduced and plates out.
