Suppose the elements X and Y combine to form two compounds and . When 0.1 mole of weighs 10 g and 0.05 mole of weighs 9 g, the atomic weights of X and Y are [2016]

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Solution

Q.
Suppose the elements X and Y combine to form two compounds ${XY}_{2}$ and $X_{3} Y_{2}$ . When 0.1 mole of ${XY}_{2}$ weighs 10 g and 0.05 mole of $X_{3} Y_{2}$ weighs 9 g, the atomic weights of X and Y are [2016]

1 40, 30

2 60, 40

3 20, 30

4 30, 20

Ans.
(1)

Let atomic weight of element X be x and that of element Y be y.

For $X Y_{2},$ $n = \frac{w}{Mol. wt.}$

$0.1 = \frac{10}{x + 2 y} \Rightarrow x + 2 y = \frac{10}{0.1} = 100$ ...(i)

For $X_{3} Y_{2},$ $n = \frac{w}{Mol. wt.}$

$0.05 = \frac{9}{3 x + 2 y} \Rightarrow 3 x + 2 y = \frac{9}{0.05} = 180$ ...(ii)

On solving equations (i) and (ii), we get $x = 40$

$40 + 2 y = 100 \Rightarrow 2 y = 60 \Rightarrow y = 30$

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