Question

A solution is prepared by dissolving 4 gram of NaOH in 40 gram of water. Find its molality?

Answer 1

Given,
Mass of solute = 4g
Molecular weight = 23 + 16 + 1 = 40 gram / mol
No. of moles of solute = 4/40 = 0.1 mol
weight of solvent = 40g = 40/1000 kg
= 0.004kg
So, Molality = mole of solute / weight of solvent
= 0.1 / 0.004
= 25 mol / kg

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Answer 2

Given data:

Mass of solute = 4g

Molecular weight = 23+16+1 = 40g/mol
where Na = 23 ; O = 16 ; H = 1

No. of moles of solute = 4/40 = 0.1mol

weight of solvent = 40g = 40/1000 = 0.004kg

Now,

Molality = No. of moles of solute/Mass of solvent in kg

=> 0.1/0.004

=> 25 kg/mol

#Hassan