Question

Calculate the mole fraction of water in a sodium hydroxide solution which has 80 g of NaOH and 54 g of H₂O. (Relative atomic masses: Na = 23, O = 16, H = 1)

Answer 1

Molar mass of NaOH = 23 (Na) + 16 (O) + 1 (H)

= 40 g/mol

Moles of NaOH = `80/40`

= 2 mol

Molar mass of H₂O = 2 + 16

= 18 g/mol

Moles of water = `54/18`

= 3 mol

Mole fraction of water = `"Moles of water"/("Moles of water" + "Moles of NaOH")` 

= `3/(3 + 2)`

= `3/5`

= 0.6