COMEDK Exam 2012 Solved Paper

Given, 39% by mass of organic solvent in benzene
∴39g of organic solvent in 100g solutiuon.
or
39g of organic solvent in 100−39=61g benzene.
Now, molar mass of organic solvent =122g∕mol
Molar mass of benzene (C6H6)=12×6+6=78g∕mol
∴ Moles of benzene (ng)=

61

78

Moles of organic solvent (nO)=

39

122

Moles fraction of benzene =

ng

ng+nO

=

61 78

61 78 + 39 122

=0.6