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  4. Suppose the elements P and Q combine to form two compounds PQ2 and P3Q2 . When 0.1 mole of PQ2 weight 10 g and 0.05 mole of P3Q2 weight 9 g, the atomic weights of P and Q are

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Q. Suppose the elements P and Q combine to form two compounds $PQ_{2}$ and $P_{3}Q_{2}$ . When 0.1 mole of $PQ_{2}$ weight 10 g and 0.05 mole of $P_{3}Q_{2}$ weight 9 g, the atomic weights of P and Q are

NTA AbhyasNTA Abhyas 2020Some Basic Concepts of Chemistry

Solution:

Let atomic weight of element P is p and that of element Q is q.

For $PQ_{2},n=\frac{w}{M o l . w t .}$

$0.1=\frac{10}{p + 2 q}$

$p+2q=\frac{10}{0.1}=100$ ...(i)

For $P_{3}Q_{2},n=\frac{w}{M o l . w t .}$

$0.05=\frac{9}{3 p + 2 q}$

$3p+2q=\frac{9}{0.05}=180$ ...(ii)

On solving equation (i) and (ii) we get q = 30

$p+2\left(\right.30\left.\right)=100$

$p=100-60=40$