Question

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

• A. When ${\chi }_A=1$ and ${\chi }_B=0$ then $P=P_A^o$
• B. When ${\chi }_B=1$ and ${\chi }_A=0$ then $P=P_B^o$
• C. When ${\chi }_A=1$ and ${\chi }_B=0$ then $P<P_B^o$
• D. When ${\chi }_B=1$ and ${\chi }_A=0$ then $P>P_A^o$

Answer 1

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

The correct options are
A When ${\chi }_A=1$ and ${\chi }_B=0$ then $P=P_A^o$
B When ${\chi }_B=1$ and ${\chi }_A=0$ then $P=P_B^o$
C When ${\chi }_B=1$ and ${\chi }_A=0$ then $P>P_A^o$
D When ${\chi }_A=1$ and ${\chi }_B=0$ then $P<P_B^o$

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, all options are correct.