KEAM 2021 Physics and Chemistry Solved Paper

we know, ‌

p∘−p

p∘

=χB=‌

nB

nA

=‌

‌ WB MB

WA MA

where,
p∘= vapour pressure of pure benzene =0.850bar
p= vapour pressure of solution =0.845 bar χB= mole fraction of solute
nB= number of moles of solute
nA= number of moles of benzene
wB= mass of solute =1g
wA= mass of benzene =39g
MA= molar mass of benzene =78g∕mol
MB= molar mass of solute = ?
∴p∘−p∕p∘=‌wB×MA∕MB×wA
=‌

0.850−0.845

0.850

=‌

1×78

MB×39

⇒‌‌MB=‌

78×0.850

0.005×39

=340gmol−1