Question

S.A compound on analysis gave Na-14.31%,S-9.97%,H-6.22%and 0-69.5%

calculate the molecular formula of the compound if all the hydrogen in the compound is present in
combination with oxygen as water of crystallization (Molecular mass of the compound is 322)​

Answer 1

Element mass % Atomic mass(g) m%/At. mass Integral ratio

Na 14.31 23 0.622 2

S 9.97 32 0.311 1

H 6.22 1 6.22 20

O 69.5 16 4.34 14

Empirical formula is therefore Na

2

SH

20

O

14

empirical mass=2×23+32+20×1+14×16=322g

Given:

Molecular mass = 322 g

∴ molecular formula =empirical formula=Na

2

SH

20

O

14

Given that all the hydrogen in the compound is reset in combination with oxygen as water of crystallisation

If water of crystallization are nH

2

O then, 2n=20

or n=10

Crystallized water is 10H

2

O remaining atoms are Na

2

SO

4

therefore, the molecule is Na

2

SO

4

.10H

2

O