The density of 20% (w/v) aqueous NaOH solution is 1.20 g.mL^–1. What is the mole fraction of water ?(molar mass of NaOH = 40g.mol^–1)

20% (w/v) aqueous NaOH solution means,

W_S= 20gm, Volume of solution=100ml

Wt. of solution=1.20x100=120gm

W_o=120-20=100gm

$$\begin{gathered} {\mathrm{n}}_{\mathrm{s}}=\frac{20}{40}=0.5 \\ {\mathrm{n}}_{\mathrm{o}}=\frac{100}{18}=5.55 \\ {\mathrm{X}}_{\mathrm{o}}=\frac{5.55}{6.05}=0.917 \end{gathered}$$