Question

The vapour pressure of two pure liquids ($A$) and ($B$) are $100$ and $80$ torr respectively. The total pressure of the solution obtained by mixing $2mol$ of ($A$) and $3$ mol of ($B$) would be:

• A. $20torr$
• B. $36torr$
• C. $88torr$
• D. $180torr$

Answer 1

The correct option is C $88torr$

Given:

Vapour pressure of pure A,$P{°}_A=100torr$

Vapour pressure of pure B, $P{°}_B=80torr$

No. Of moles of A=2

No. Of moles of B =3

Solution:

Mole fraction of A=$\frac{2}{2+3}=0.4$

Mole fraction of B =$\frac{3}{2+3}=0.6$

According to Dalton's law of partial pressure,

Total pressure=$P{°}_1\times x_A+P{°}_B\times x_B$

$\Rightarrow P_T=100\times 0.4+80\times 0.6$

$\Rightarrow P_T=40+48torr$

Therefore, $P_T=88torr$

Hence, option C is correct.