Solutions Question 409
Question: An aqueous solution containing liquid A $ (M.Wt.=128) $ 64% by weight has a vapour pressure of 145 mm. Find the vapour pressure of pure A. If that of water is 155 mm at the same temperature.
Options:
A) 205 mm
B) 2.05 mm
C) 1.05 mm
D) 105 mm
Show Answer
Answer:
Correct Answer: D
Solution:
According to Raoult’s law for liquid mixtures. $ P=P_{A}+P_{B} $ $ P=P_A^{0}\times \frac{\frac{W_{A}}{M_{A}}}{\frac{W_{A}}{M_{A}}+\frac{W_{B}}{M_{B}}}+P_B^{0}\times \frac{\frac{W_{B}}{M_{B}}}{\frac{W_{A}}{M_{A}}+\frac{W_{B}}{M_{B}}} $ $ P=145=P_A^{0}\times \frac{\frac{64}{128}}{\frac{64}{128}+\frac{36}{18}}+155\times \frac{\frac{36}{18}}{\frac{64}{128}+\frac{36}{18}} $ $ P_A^{0}=105,mm $
