Question

The vapour pressure of the solution of two liquids $A(p^{\circ }=80mm)$ and $B(p^{\circ }=120mm)$ is found to be 100 mm when $X_A$ = 0.4. The result shows that

• A. Solution exhibits ideal behaviour
• B. Solution shows positive deviation
• C. Solution shows negative deviation
• D. Solution will show positive deviation for lower concentration and negative deviation for higher concentration.

Answer 1

The correct option is C

Solution shows negative deviation

Expected total pressure

$=P_A^{\circ }{X}_A+P_B^{\circ }{X}_B$

= (80) (0.4) + (120) (0.6)

= 32 + 72

= 104 mm

Actual pressure (100 mm) is lower than expected pressure (104 mm). Hence, it shows negative deviation.