Question

A solution contains 72.0 g of `HCl` and 468 g of `C_6H_6`. What is the mole fraction of benzene?

Answer 1

The mole fraction of benzene is 0.752.

Explanation:

The mole fraction of a substance in a solution is equal to the moles of the substance divided by the total moles of all substances in the solution.

`"Mole fraction"` `=` `"mol X"/"mol X+mol Y"`

The mass of each compound needs to be converted to moles by dividing the mass by its molar mass.

First determine the molar mass of both compounds.

Molar Mass HCl:

`(1xx1.008 "g/mol")+(1xx35.45 "g/mol")="36.458 g/mol"`

Molar Mass `"C"_6"H"_6"`:

`(6xx12.011"g/mol")+(6xx1.008"g/mol")="78.114 g/mol"`

Next determine the moles present for each compound by dividing the mass given in the question by its molar mass.

Moles HCl:

`"72.0 g HCl"xx"1 mol HCl"/"36.458 g HCl"="1.974 mol HCl"`

Moles `"C"_6"H"_6":`

`"468 g C"_6"H"_6xx("1 mol C"_6"H"_6)/("78.114 g C"_6"H"_6)="5.991 mol C"_6"H"_6"`

Determine the Mole Fraction of Benzene

`"C"_6"H"_6"` `rArr` `"5.991"/"5.991+1.974"="0.752"`