Question

(i) State Henry’s Law. Give two applications of it. 
(ii) Draw the vapour pressure-mole fraction curve for a non-ideal solution having positive deviation, if A and B are the two volatile components.

• A.
• B.
• C.
• D.

Hint:

Positive deviation usually leads to the formation of a minimum boiling azeotrope, where the solution boils at a lower temperature than either pure component!

Answer 1

The Correct Option is A

Step 1: Henry's Law Definition and Formula.
Henry's Law states that at constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas present above the surface of the liquid or solution.

p = KH × x

Where p is the partial pressure, x is the mole fraction of the gas in the solution, and KH is Henry's law constant.

Step 2: Applications of Henry's Law.

1. Soft Drinks: To increase the solubility of CO2 in soft drinks and soda water, the bottle is sealed under high pressure.

2. Scuba Diving: To avoid "the bends" (painful nitrogen bubbles in blood), scuba divers use tanks filled with air diluted with helium, which is less soluble in blood.

Step 3: Positive Deviation Curve.
In solutions showing positive deviation, A–B interactions are weaker than A–A or B–B interactions. This causes the vapour pressure of each component and the total vapour pressure to be higher than that expected from Raoult's law.