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JAMB Physics 2013 Paper

Question : 38

Total: 43

If a current of 2.5A flows through an electrolyte for 3 hours and 1.8g of a substance is deposited, what is the mass of the substance that will be deposited if a current of 4A flows through it for 4.8 hours?

2.4g
3.2g
4.6g
4.8g

Validate

Solution:

Concept:

According to Faraday’s first law of electrolysis, the mass deposited is directly proportional to the quantity of electricity passing through the electrolyte.

Explanation:

The law is expressed as

m = zIt

, so for the same electrolyte,

z

is constant.

Thus,

\frac{m_2}{m_1} = \frac{I_2 t_2}{I_1 t_1}

First experiment:

I_1 = 2.5

t_1 = 3

hours,

m_1 = 1.8

Second experiment:

I_2 = 4

t_2 = 4.8

hours.

Substitute into the relation:

m_2 = 1.8 \times \frac{4 \times 4.8}{2.5 \times 3}

Simplify:

4 \times 4.8 = 19.2

and

2.5 \times 3 = 7.5

m_2 = 1.8 \times \frac{19.2}{7.5} = 1.8 \times 2.56 = 4.608 \, \text{g}

Therefore, the deposited mass is approximately

4.6

Answer:

4.6

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