Question

if you are given a 2M NAOH solution having density 1g/mL, then find the molality of solution.

Answer 1

Explanation:

Molar mass of NaOH = 40

Molarity = 2

Molality = molarity / (d - molarity × molecular mass of solute)

Molality = 2 ×1000/( 1000 - 2 × 40)

Molality = 2×1000 /920 = 2.17 m

Answer 2

The molality of the solution is given as 2.17 m

Given : Molarity of NaOH solution is 2 M

Density of NaOH solution is 1g/mL

To Find : Molality of the solution

Solution : The molality of the solution is given as 2.17 m

It is given that the molarity of NaOH solution is 2 M  and the density of NaOH solution is 1g/mL

We have to find the molality of the solution

Now the relationship between molality and molarity is given as

$\frac{1}m} = \frac{d}{M} - \frac{M'}{1000}$

where m is molality

M is molarity

M' is molar mass of the solute

d is density of the solute

Here M = 2 M

m = ?

d = 1g/mL

M' = Molar mass of NaOH is sum of atomic masses of all the atoms

Na = 22.989 g/mol , O = 15.999 g/mol , H = 1.008 g/mol

Adding all the molar mass that forms NaOH

22.989 +15.999 +1.008 = 39.996 or 40 approx

M' = 40

Putting these value in the above equation

$\frac{1}{m} = \frac{1}{2} - \frac{40}{1000}$

$\frac{1}{m} = \frac{1}{2} - \frac{1}{25}$

$\frac{1}{m}$ = 0.5 - 0.04

$\frac{1}{m}$ = 0.46

m = $\frac{1}{0.46}$

m = 2.17

So molality of solution is 2.17 m

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