5 g sample contain only `Na_(2)CO_(3)` and `Na_(2)SO_(4)` . This sample is dissolved and the volume made up to 250 mL. 25 mL of this solution neutralizes 20 mL of 0.1 M `H_(2)SO_(4)`.
Calcalute the % of `Na_(2)SO_(4)` in the sample .

Options

A. 42.4
B. 57.6
C. 36.2
D. 0.576

Answer

B

Explanation

Only `Na_(2)CO_(3)` reacts with `H_(2)SO_(4)`.
`Na_(2)CO_(3) +H_(2)SO_(4) to Na_(2)SO_(4) +H_(2)CO,_(3)`
m-moles of `Na_(2)CO_(3)="m-moles of "H_(2)SO_(4)=20 xx 0.1 = 2`
 m-moles of `Na_(2)CO_(3)` in 250 mL solution
`=(250)/(25) xx 2=20`
wt. of `Na_(2)CO_(3)= 20 xx 106 xx 10^(-3)=2.12 g`
% of `Na_(2)CO_(3)=(2.12)/(5) xx 100=42.4`
`:. % of Na_(2)SO_(4)=100-42.4=57.6`