Question

The molar mass of $CuS{O}_4.5H_{2}O$ is 249. Its equivalent mass in the reaction (a) and (b) would be:
(a) Reaction $CuS{O}_4+KI\to$ product
(b) Electrolysis of $CuS{O}_4$ solution

• A. (a) 249 (b) 249
• B. (a) 124.5 (b) 124.5
• C. (a) 249 (b) 124.5
• D. (a) 124.5 (b) 249

Answer 1

Answer: (B)

(a) 124.5 (b) 124.5

In water, ${CuSO}_4\cdot 5H_{2}O$ dissociates into ${Cu}^{2+}$ & ${SO}_4^{2-}$. The ions are doubly charged. Hence half as much is needed to react with a compound that dissociates into singly charged species.

(a) Reaction of ${CuSO}_4+KI⟶$ products.

Eq. wt of ${CuSO}_4=249/2=124.5$

(b) Electrolysis of ${CuSO}_4$

At Cathode ${\underset{+2}{Cu}}^{2+}+{2e}^{-}⟶\underset{0}{Cu}$

$\therefore$ Charge in oxidation state $=2=n-$factor

$\therefore$ Eq. wt $=\frac{249}{2}=124.5$