Question

Objective Type Questions
The boiling temperature and composition curve of
"water ethanol” solution is given below.

At point 'C', the mixture has ethanol 95.8% by
weight in vapour phase. If this solution is boiled at
78.13°C, then percentage by weight of water in
liquid phase is (boiling temperature
(1) 95.8%
(2) 4.2%
(3) 80.8%
(4) 43.5%
78.13°C)​

Answer 1

Answer:

(2) 4.2%

Explanation:

As, Pure water boils at 100 °C, and pure ethanol boils at 78.5 °C, but a mixture of water and ethanol will boil at some point in between.

In the case of mixtures of ethanol and water, this minimum occurs with 95.8% by mass of ethanol in the mixture. The boiling point of this mixture is 78.13°C, compared with the boiling point of pure ethanol at 78.5°C, and water at 100°C.

So, the percentage weight of water in liquid phase is 100- 95.8= 4.2%