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Pottassium selenate is isomorphous with potassium sulphate and contains 45.42% selenium by weight.Calculate the atomic weight of selenium.Also report the equivalent weight of potassium selenate.

$\begin{array}{1 1}(a)\;118.2,130.1\\(b)\;120,131\\(c)\;121.3,132.4\\(d)\;122.1,129.2\end{array}$

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Pottassium selenate is isomorphous to $K_2SO_4$ and thus its molecular formula is $K_2SeO_4$
Now mol.wt of $K_2SeO_4=(39\times 2+a+4\times 16)$
$\Rightarrow 142+a$
Where 'a' is at.wt of Se
$(142+a)g\;K_2SeO_4$=Se a g
100g $K_2SeO_4=\large\frac{a\times 100}{142+a}$
$\%$ of se=45.42
$\approx 118.2$
Also equivalent weight of $K_2SeO_4=\large\frac{Mol.wt}{2}$
$\Rightarrow \large\frac{2\times 39+118.2+64}{2}$
$\Rightarrow 130.1$
Hence (a) is the correct answer.
answered Oct 31, 2013 by sreemathi.v

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