Copper of 0.2g and silver of 1.2g are deposited when current is passed through copper and silver voltameter…

Analysis

This question is based on Faraday’s Laws of Electrolysis. Specifically, it deals with the relationship between the mass of a substance deposited during electrolysis and its electrochemical equivalent (Z).

Concept

According to Faraday’s second law of electrolysis, when the same quantity of electricity ($Q$) is passed through different electrolytes connected in series, the mass ($m$) of the substance deposited is directly proportional to its electrochemical equivalent ($Z$).

The formula is:

Where:

• $m_1$ = mass of copper = $0.2\text{ g}$
• $Z_1$ = electrochemical equivalent of copper = $0.00028\text{ gC}^{-1}$
• $m_2$ = mass of silver = $1.2\text{ g}$
• $Z_2$ = electrochemical equivalent of silver = ?

Solution

1. Set up the equation: $$\frac{m_{copper}}{Z_{copper}} = \frac{m_{silver}}{Z_{silver}}$$

2. Substitute the known values: $$\frac{0.2}{0.00028} = \frac{1.2}{Z_{silver}}$$

3. Cross-multiply to solve for $Z_{silver}$: $$0.2 \times Z_{silver} = 1.2 \times 0.00028$$ $$0.2 \times Z_{silver} = 0.000336$$

4. Divide by 0.2: $$Z_{silver} = \frac{0.000336}{0.2}$$ $$Z_{silver} = 0.00168\text{ gC}^{-1}$$

5. Convert to standard form: $$0.00168 = 1.68 \times 10^{-3}\text{ gC}^{-1}$$

Conclusion

Comparing our result with the given options, we find that it matches option A.

Exam Tip

When dealing with electrolysis problems in JAMB, always check if the substances are in series. If they are, the charge ($Q = It$) is the same for both. If you ever forget the formula, remember that mass is directly proportional to the electrochemical equivalent; just set up a simple ratio!