Question

Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.

Answer 1

Let the total mass of the solution be 100 g, and the mass of benzene be 30 g.

∴ Mass of carbon tetrachloride = (100 − 30) g

= 70 g

Molar mass of benzene (C₆H₆) = (6 × 12 + 6 × 1) g mol⁻¹

= 78 g mol⁻¹

∴ Number of moles of C₆H₆ = `"Mass"/"Molar mass"`

= `(30  "g")/(78  "g mol"^(−1))`

= 0.385 mol

Molar mass of carbon tetrachloride (CCl₄) = 1 × 12 + 4 × 35.5

= 154 g mol⁻¹

∴ Number of moles of CCl₄ = `"Mass"/"Molar mass"`

= `(70  "g")/(154  "g mol"^(−1))`

= 0.455 mol

Thus, the mole fraction of C₆H₆ is given as:

`("Number of moles of C"_6"H"_6)/("Number of moles of C"_6"H"_6+"Number of moles of CCl"_4)`

= `0.385/(0.385+0.455)`

= 0.458

∴ Mole fraction of CCl₄ = 1 − 0.458 = 0.542