The density of 2 M aqueous solution of NaOH is 1.28 . The molality of the solution is [Given that molecular mass of NaOH = 40 g ] [2019]

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Solution

Q.
The density of 2 M aqueous solution of NaOH is 1.28 $g / {cm}^{3}$ . The molality of the solution is [Given that molecular mass of NaOH = 40 g ${mol}^{- 1}$ ] [2019]

1 1.20 m

2 1.56 m

3 1.67 m

4 1.32 m

Ans.
(3)

Density = 1.28 g/cc, Conc. of solution = 2 M

Molar mass of NaOH = 40 g ${mol}^{- 1}$

Volume of solution = 1 L = 1000 mL

Mass of solution $= d \times V = 1.28 \times 1000 = 1280$ g

Mass of solute $= n \times Molar mass = 2 \times 40 = 80$ g

Mass of solvent = (1280 - 80) g = 1200 g

$∴$ Molality $= \frac{2 \times 1000}{1200} = 1.67$ m

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