Question

the vapour pressure of pure water at 22°c is 21 torr . calculate the new vapor pressure of 245 g of water mixed with 45.2 g of ethyl alcohol​

Answer 1

Mol. mass of ethyl alcohol =C

2

H

5

OH=46

No. of moles of ethyl alcohol =

46

60

=1.304

Mol. mass of methyl alcohol =CH

3

OH=32

No. of moles of methyl alcohol =

32

40

=1.25

′

X

A

′

, mole fraction of ethyl alcohol =

1.304+1.25

1.304

=0.5107

′

X

B

′

, mole fraction of methyl alcohol =

1.304+1.25

1.25

=0.4893

Partial pressure ethyl alcohol =X

A

p

˙

A

0

=0.5107×44.5=22.73mmHg

Partial pressure methyl alcohol =X

B

p

˙

B

0

=0.4893×88.7=73.40mmHg

Total vapour pressure of solution =22.73+43.40=66.13mmHg

Mole fraction of methyl alcohol in the vapour

=

Total vapour pressure

Partial pressure of CH

3

OH

=

66.13

43.40

=0.6563