Question

0.222g of a divalent metal is deposited when a current of 0.45A is passed through a solution of its salt for 25 minutes using platinum electrodes. Calculate the relative atomic mass of the metal.

Answer 1

According to the Faraday's laws of electrolysis, the quantity of metal $n$ deposited on the electrode is proportional to the quantity of charge $Q = It$ which has flown in electrolysis time $t$ when a current $I$ is passed through the solution:

$n = \frac{It}{zF}$ ,

where $z$ is the valence of the metal and $F$ is the Faraday's constant, equal to 96487 C/mol.

Therefore, the number of the moles of the metal deposited when a current of 0.45 A is passed through a solution of its salt for 25 minutes (25·60 seconds) is:

$n = \frac{0.45 \text{A}\cdot25\cdot60\text{s}}{2·96487\text{C/mol}} = 3.50·10^{-3}$ mol.

The relative atomic mass of the metal is the ratio of its mass to its number of the moles:

$M = \frac{m}{n} = \frac{0.222\text{g}}{3.50·10^{-3}\text{mol}} = 63.5$ g/mol.

Answer: the relative atomic mass of the metal is 63.5 g/mol. This metal is copper Cu.