Question

Potassium selenate is isomorphous with potassium sulphate and contains $50.0$ % of Se. Find the atomic weight of Se.

• A. 142
• B. 71
• C. 47.33
• D. 284

Answer 1

Answer: (A)

142

$K_{2}S{O}_4$ and $K_{2}Se{O}_4$ are isomorphous.

Mol. wt. of $K_{2}Se{O}_4$ $\Rightarrow 39\times 2+x+64=142+x$

$(142+x)g$ of $K_{2}Se{O}_4\Rightarrow x$ g of Se

$100$ g of $K_{2}Se{O}_4\Rightarrow \frac{x}{142+x}\times 100$

$\therefore \frac{x}{142+x}\times 100=50$

$\therefore x=142$.