Verified Solution • 2025–26 Session moderate

QJEEAdv20Ch12fa: JEE Advanced 2020 Chemistry - Class 12 JEEAdv20Ch12fa Solution: Liquids A and B form ideal solution for all compositions of A…

Liquids A and B form ideal solution for all compositions of A and B at 25 ∘^\circ C. Two such solutions with 0.25 and 0.50 mole fractions of A have the total vapour pressure of 0.3 and 0.4 bar, respectively. What is the vapour pressure of pure liquid B in bar?

Step-by-Step Verified Solution

Using Raoult's law equation for a mixture of volatile liquids.

PT=pAoχA+pBoχB{P_T} = p_A^o{\chi _A} + p_B^o{\chi _B}

0.3=0.25χpAo+0.75χpBo0.3 = 0.25\chi p_A^o + 0.75\chi p_B^o ....(i)

0.4=0.5χpAo+0.5χpBo0.4 = 0.5\chi p_A^o + 0.5\chi p_B^o ....(ii)

By solving equation (i) and (ii)

pAop_A^o = 0.6 bar and pBop_B^o = 0.2 bar

Thus, the vapour pressure of pure liquid B in bar is 0.2.

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