Question

Potassium selenate is isomorphous with potassium sulphate and contains $50.5 \%$ of Se. Find the atomic weight of $Se$.

• A. 142
• B. 71
• C. 47.33
• D. 284

Answer 1

Answer: (A)

$K _2 SO _4$ and $K _2 SeO _4$ are isomorphous.
$ K _2 SeO _4$
$ \Rightarrow 39 \times 2+x+64=142+x $
$(142+x) g {\text {of } K _2 SeO _4 \Rightarrow x g \text { of } Se } $
$ 100 g \text { of } K _2 SeO _4 \Rightarrow \frac{x}{14+x} \times 100 $
$ \therefore \frac{x}{142+x} \times 100=50$
$ \therefore x=142$