Solutions — Important Questions

Increase the solubility of CO₂ in the drink

Step 1: According to Henry's law, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid. Step 2: By sealing the bottle under high pressure of CO₂, the partial pressure of CO₂ above the liquid is increased. Step 3: This increases the solubility of CO₂ in the drink, keeping more gas dissolved and making the drink fizzy. Step 4: When the bottle is opened, pressure drops, CO₂ escapes as bubbles. Step 5: This is a direct application of Henry's law in everyday life.

Directly proportional to its mole fraction in solution

Step 1: Raoult's law states: p₁ = x₁ × p₁⁰, where p₁ is partial vapour pressure, x₁ is mole fraction, and p₁⁰ is vapour pressure of pure component. Step 2: Since p₁⁰ is a constant at a given temperature, p₁ is directly proportional to x₁ (mole fraction). Step 3: It is NOT equal to pure component vapour pressure because x₁ is always less than 1 in a solution. Step 4: 'Inversely proportional' is incorrect — more moles means more vapour pressure, not less. Step 5: It is definitely not independent of mole fraction, as the equation clearly shows a direct relationship.

Lower

Step 1: In a pure liquid, the entire surface is occupied by solvent molecules that can evaporate freely. Step 2: When a non-volatile solute is added, some surface is now occupied by solute molecules. Step 3: This reduces the fraction of the surface available to solvent molecules, so fewer solvent molecules escape into the vapour phase. Step 4: As a result, the vapour pressure of the solution is lower than that of the pure solvent. Step 5: This is the basic principle behind relative lowering of vapour pressure, which is a colligative property.

Optical rotation

Step 1: Colligative properties depend only on the number of solute particles in solution, not on their nature (identity). Step 2: The four colligative properties are: (1) Relative lowering of vapour pressure, (2) Elevation of boiling point, (3) Depression of freezing point, and (4) Osmotic pressure. Step 3: Optical rotation is a physical property that depends on the nature (structure) of the solute, specifically chiral molecules. Step 4: It is not related to the number of solute particles, so it is NOT a colligative property. Step 5: The other three options — elevation of boiling point, depres