Ncert Exercises & Solutions

1.2 Calculate the mass per cent of different elements present in sodium sulphate ( ${Na}_{2} {SO}_{4}$ ).

The molecular formula of sodium sulfate is ${Na}_{2} {SO}_{4}$ .
Molar mass of ${Na}_{2} {SO}_{4}$ = [(2 × 23.0) + (32.066) + 4 (16.00)]
= 142.066 g

The mass percent of an element = $\frac{Mass of thet element in the compound}{Molar mass of the compound} \times 100$
$∴$ The mass percent of sodium:

$= \frac{46.0 g}{142.066} \times 100$
$= 32.379$
$= 32.4 %$

The mass percent of sulphur:

$= \frac{32.066 g}{142.066} \times 100$
$= 22.57$
$= 22.6 %$

The mass percent of oxygen:

$= \frac{64.0 g}{142.066} \times 100$
$= 45.049$
$= 45.05 %$