Question

The density of a $3M$ sodium thiosulphate $(Na_2S_2O_3)$ solution is $1.25\, g/mL$ . Calculate the percent by weight of sodium thiosulphate

• A. $12.64\%$
• B. $37.92\%$
• C. $0.87\%$
• D. $63.21\%$

Answer 1

Answer: (B)

$37.92\%$

Answer 2

The correct answer is B:37.92%
Molecular weight of
$Na_2S_2O_3 = 2 \times 23 + 2 \times 32 + 3 \times 16$
$= 158$
From molarity
$\frac{\%\space by \space weight \space of \space solute\times density \space of \space solution \times 10}{M}$
$3 = \frac{\%{\text{by weight of} Na_2S_2O_3 \times 1.25 \times 10}}{158}$
$\therefore \%$ by weight of $Na_2S_2O_3$
$= \frac{3\times 158}{1.25 \times 10}$
$= 37.92\%$