Question

Calculate mole fraction of solute if molarity of solution is 20% ($\frac{W}{W}$) aqueous solution of NaOH.

• A. 0.2
• B. 0.15
• C. 0.1
• D. none of these

Answer 1

The correct option is C 0.1

$20$% W/W aqueous solution of NaOH

$20g$ of NaOH in $100g$ of solution

Solution=solute+solvent

$100=20+$solvent

$80g=$solvent

$20g$ of NaOH in $80g$ of water

$n_{NaOH}=\frac{20}{40}=\frac{1}{2}=0.5n_{H_{2}O}=\frac{80}{18}=4.44$

Mole fraction of NaOH$=\frac{n_{NaOH}}{n_{NaOH}+n_{H_{2}O}}=\frac{0.5}{0.5+4.44}=\frac{0.5}{4.94}=0.101$

Thus, Mole fraction of solute is $0.1$