The density of $\mathrm{NaOH}$ solution is $1.2 \mathrm{~g} \mathrm{~cm}^{-3}$. The molality of this solution is________ $\mathrm{m}$.
(Round off to the Nearest Integer)
[Use : Atomic masses : $\mathrm{Na}: 23.0 \mathrm{u} \quad \mathrm{O}: 16.0 \mathrm{u}$ $\mathrm{H}: 1.0 \mathrm{u}$
Density of $\mathrm{H}_{2} \mathrm{O}: 1.0 \mathrm{~g} \mathrm{~cm}^{-3}$ ]
Consider $1 \ell$ solution
mass of solution $=(1.2 \times 1000) \mathrm{g}$
$=1200 \mathrm{gm}$
Neglecting volume of $\mathrm{NaOH}$
Mass of water $=1000 \mathrm{gm}$
$\Rightarrow$ Mass of $\mathrm{NaOH}=(1200-1000) \mathrm{gm}$
$=200 \mathrm{gm}$
$\Rightarrow$ Moles of $\mathrm{NaOH}=\frac{200 \mathrm{~g}}{50 \mathrm{~g} / \mathrm{mol}}=5 \mathrm{~mol}$
$\Rightarrow$ molality $=\frac{5 \mathrm{~mol}}{1 \mathrm{~kg}}=5 \mathrm{~m}$
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