text: # A solution contains 72.0 g of HCl and 468 g of C_6H_6. What is the mole fraction of benzene?
  
  Sep 15, 2016
  
  #### Answer:
  
  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.
  
  $\text{Mole fraction}$$=$$\text{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 $\text{C"_6"H"_6}$:
  
  (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:
  
  $\text{72.0 g HCl"xx"1 mol HCl"/"36.458 g HCl"="1.974 mol HCl}$
  
  Moles $\text{C"_6"H"_6} :$
  
  $\text{468 g C"_6"H"_6xx("1 mol C"_6"H"_6)/("78.114 g C"_6"H"_6)="5.991 mol C"_6"H"_6}$
  
  Determine the Mole Fraction of Benzene
  
  $\text{C"_6"H"_6}$$\Rightarrow$$\text{5.991"/"5.991+1.974"="0.752}$
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