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A compound on analysis was found to cont...

A compound on analysis was found to contain the following composition :
`Na=14.31%,S=9.97%,O=69.50 %and H=6.22 %`
Calculate the molecular formula of the compound assuming that the whole of hydrogen in the compound is present as water of crystallisation. Molecular mass of the compound is 322.

Text Solution

Verified by Experts

Step I. Calculation of empirical formula:

Empirical formula of the compound is `Na_(2)SH_(20)O_(14)`
Step. II Calculation of molecular formula
Empirical formula mass
`=2 xx At. "mass of Na + At. mass of S" + 20 xx At. "mass of" H + 14 xx "At. mass of O"`
`=2 xx 23 +1 xx 32 + 20 xx 1 + 14 xx 16 = 322`
Now, `n=("molecular mass")/("Empirical formula mass") = 322/322 =1`
Molecular formula `=(Na_(2)SH_(20)O_(14))=Na_(2)SH_(20)O_(14))`.
Since all hydrogen atoms are present in combination with oxygen as water therefore, it means that all the 20 hydrogen atoms must be combined with 10 atoms of oxygen to form 10 molecules of water of crystallisation. The remaining 4 oxygen atoms are present with the compound Thus,
Molecular formula of the compound `=Na_(2)SO_(4).10H_(2)O`.
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