Question

The density of $3M$ solution of $NaCl$ is $1.25gm{l}^{-1}$. The molality of the solution is:

• A. $2.79$ m
• B. $1.79$ m
• C. $3.5$ m
• D. $5.58$ m

Answer 1

Answer: (A)

$2.79$ m

The relationship between the density (d), molarity (M), molality (m) and gram molecular weight (GMW) is,

$m=\frac{M\times 1000}{1000\times d-M\times GMW}$

Substituting values in the above expression, we get

$m=\frac{3\times 1000}{1000\times 1.25-3\times 58.5}=2.79m$

Hence, option A is correct.