Question

Total vapour pressure of mixture of 1 mol A (p_A⁰ = 150 torr) and 2 mol B (p_B⁰ = 240 torr) is 200 torr. In this case -

• A. There is positive deviation from Raoult's law
• B. There is negative deviation from Raoult's law
• C. There is no deviation from Raoult's law
• D. Molecular masses of A and B are also required for calculating the deviation

Answer 1

Answer: (B)

There is negative deviation from Raoult's law

Answer 2

P_s = P_A⁰ X_A + P_B⁰ X_B

= $\left( 150 \times \frac { 1 } { 3 } \right)$ + $\left( 240 \times \frac { 2 } { 3 } \right)$= 210

DP_mix = P_exp – P_theo = –ve