SOLUTION :
Formula of potassium sulphate : $K _{2} SO _{4}$
and hence formula of pot. chromate : $K _{2} CrO _{4}$
Let the atomic wt. of $Cr$ be $x$. Then mol. wt. of
$K _{2} CrO _{4}=39 \times 2+x+4 \times 16=142+x$
$\therefore(142+x)$ g potassium chromate contains $x g Cr$
$\therefore 100 g$ potassium chromate contains $\frac{x \times 100}{142+x} g$
Given that $\%$ of $C r=26 \cdot 79, \therefore \frac{100 x}{142+x}=26 \cdot 79$
or, $\quad 100 x=26 \cdot 79(142+x)=26 \cdot 79 x+3804 \cdot 18$
or, $\quad x(100-26 \cdot 79)=3804 \cdot 18, x=\frac{3804 \cdot 18}{73 \cdot 21}=51 \cdot 96$
Hence, atomic wt. of chromium $= 5 1 . 9 6$.
