Test Index

JAMB Chemistry 2019 Paper

Question : 48

Total: 80

[1 faraday = 96500C, Mg = 24]

Solution:

Concept:

Faraday's first law of electrolysis relates the mass of substance deposited to the charge passed and the valency of the ion.

Explanation:

Convert the time to seconds.

2\ \text{hours}\ 30\ \text{minutes} = 150\ \text{minutes} = 9000\ \text{s}

Calculate the total charge,

Q = I \times t

Q = 2 \times 9000 = 18000\ \text{C}

In molten

\mathrm{MgCl}_2

, the cathode reaction is:

\mathrm{Mg}^{2+} + 2e^- \rightarrow \mathrm{Mg}

2 \times 96500\ \text{C}

of charge deposits

24\ \text{g}

of magnesium.

Let the mass deposited by

18000\ \text{C}

x

x = \frac{24 \times 18000}{2 \times 96500} = \frac{432000}{193000} \approx 2.24\ \text{g}.

The closest option to this value is

2.00\ \text{g}

Answer:

2.00\ \text{g}

Go to Question:

Prev Question

Next Question