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Crystals of Salts

Hydrated Calc...

Question

Hydrated Calcium Sulfate $[C a S O_{4} . x H_{2} O]$ contains 21% (by mass)of water of crystallization. The number of molecules of water of crystallization, i.e., 'x' in the hydrate compound is:
(Ca=40, S=32, O=16, H=1)

A

1

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B

2

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C

4

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D

5

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Solution

The correct option is B 2
$[C a S O_{4} . x H_{2} O]$
Molar mass $= (136 + 18 x)$ gm
% of water in hydrate compound $= 18 x \times \frac{100}{(136 + 18 x)} = 21$
$x = 2$
So, compound is $C a S O_{4} .2 H_{2} O$ .

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