The density of 2 ; M aqueous solution of NaOH is 1.28 ;g / cm^ 3 … - Vidyadip

MCQ

The density of $2\; \mathrm{M}$ aqueous solution of $\mathrm{NaOH}$ is $1.28 \;\mathrm{g} / \mathrm{cm}^{3} .$ The molality of the solution is.....$m$ [Given that molecular mass of $\mathrm{NaOH}=40 \;\mathrm{g} \mathrm{mol}^{-1}$]

A
$1.20 $
B
$1.56$
✓
$1.67$
D
$1.32$

✓

Answer

Correct option: C.

$1.67$

c
$2 \mathrm{M}$ solution of $\mathrm{NaOH}$ means 2 mole $\mathrm{NaOH}$ is present in $1 \mathrm{L}$ solution; density $=1.28 \mathrm{g} / \mathrm{ml}$

mass of solution $=$ volume of solution $\times$ density $=1000 \times 1.28$

$=1280 \mathrm{g}$

mass of solvent $=$ mass of solution $-$ mass of solute $=1280-80$

$=1200 \mathrm{g}$

molality $=\frac{2}{1200} \times 1000=\frac{20}{12}=\frac{10}{6}=\frac{5}{3}=1.67 \mathrm{m}$

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