Question

Find the molarity out solution in which mole fraction of NaOH is 0.2 and density is 1.2g/ml

Answer 1

Answer : The molarity of solution is 10.71 mole/L

Solution : Given : mole fraction of NaOH = 0.2

0.2 moles of $NaOH$ in 1 mole of the solution, Thus (1-0.2)=0.8 moles of solvent i.e. water.

Molar mass of $NaOH$ = 40 g/mole

Mass of solute ($NaOH)=moles\times \text{Molar mass}$

Mass of $NaOH=0.2moles\times 40g/mol=8g$

Moles of water (solvent) = 0.8

Mass of $H_2O$(solute) = $0.8moles\times 18g/mole=14.4g$

Mass of solution = Mass of solute + Mass of solvent = 8 + 14.4 = 22.4 g

Now we have to calculate the volume of solution.

$Volume=\frac{Mass}{Density}=\frac{22.4}{1.2g/ml}=18.67ml$  

Molarity : It is defined as the number of moles of solute present in one liter of solution.

Formula used :

$Molarity=\frac{n}{V_s}$

where,

n = moles of solute = 0.2

$V_s$ = volume of solution in liter = 0.01867 L

$Molarity=\frac{0.2moles}{0.01867L}=10.71mole/L$

Therefore, the molarity of solution is 10.71 mole/L