JAMB Chemistry 2019 Paper

Concept:Faraday’s laws of electrolysis relate the mass of metal discharged to the quantity of electricity used.The cost of electricity is proportional to the number of Faradays required.Explanation:For metal X, $X^{2+} + 2e^- \to X$, so 1 mole of X requires 2 moles of electrons.Since the atomic mass of X is 63 g, $2F$ discharges 63 g of X.Let the Faradays needed for 6.0 g of X be $q$.$\frac{q}{6.0} = \frac{2F}{63}$$q = \frac{6.0 \times 2}{63}F = \frac{4}{21}F$Given: $\frac{4}{21}F$ costs ₦12.00.Therefore, $1F$ costs ₦12.00 $\times \frac{21}{4}$ = ₦63.00.For metal Y, $Y^{3+} + 3e^- \to Y$, so 1 mole of Y requires 3 Faradays.Since the atomic mass of Y is 27 g, $3F$ discharges 27 g of Y.For 9.0 g of Y, the Faradays required are:$\frac{9.0}{27} \times 3F = 1F$Since $1F$ costs ₦63.00, discharging 9.0 g of Y costs ₦63.00.Answer:₦63.00, which is option C.