Question

The following is a graph plotted between the vapour pressure of two volatile liquids against their respective mole fractions. Which of the following statements are correct?

• A. When $x_A=1and{x}_B=0,thenP=P_A^0$
• B. When $x_B=1and{x}_A=0,thenP=P_B^0$
• C. When $x_A=1and{x}_B=0,thenP<P_B^0$
• D. When $x_B=1and{x}_A=0,thenP>P_A^0$

Answer 1

Answer: (A), (B), (C), (D)

The correct options are
A When $x_A=1and{x}_B=0,thenP=P_A^0$
B When $x_B=1and{x}_A=0,thenP=P_B^0$
C When $x_A=1and{x}_B=0,thenP<P_B^0$
D When $x_B=1and{x}_A=0,thenP>P_A^0$

From the graph, we can observe that $p_A^0<p_B^0$

The vapour pressure at any $x$ can be given as $P=(p_B^0-p_A^0)\times x_B+p_A^0$

Also, $x_A+x_B=1$ (Binary system)

So, at $x_A=1,x_B=0andP=p_A^0<p_B^0$

and

at $x_B=1,x_A=0andP=p_B^0>p_A^0$

Hence, options A, B, C and D are correct