KEAM 2012 Physics and Chemistry Paper

Mole fraction, x=‌

m

w m +‌ W M

(where, w and m represent the mass and molar mass of solute and W and M represent the mass and molar mass of solvent.)
‌

1

x

=‌

‌ w m + W M

w m

‌

1

x

=1+‌

W×m

M×w

×‌

1000

1000

‌

1

x

=1+‌

1000

M×m

(∵ Molality m=‌

w×1000

m×W

)
=1+‌

1000

18×4.5

( ∵ Molar mass of H2O=18gmol−1 )
=1+‌

1000

81

=‌

1081

81

=13.34
x=‌

1

13.34

=0.075