Test: Ideal and non ideal solutions & Colligative properties(19 Sep) - JEE MCQ

As A is more volatile, vapour phase would be richer in A. Hence
(x_A)_liquid < (x_A)_vapour

Azeotropes are formed by the solutions which show deviations from ideal behaviour.

Acetone + ethyl alcohol solution shows positive deviation while acetone + chloroform shows negative deviation.
Other examples:
Positive deviations - Acetone + ethyl alcohol,
acetone + benzene, water + ethyl alcohol
Negative deviations - Nitric acid + water,
benzene + chloroform

(iii) and (iv) will form ideal solutions hence do not form azeotropes. Azeotropes have same composition in liquid and vapour form when distilled.

To determine which binary mixtures will have the same composition in the liquid and vapor phases, we need to identify mixtures that form ideal solutions. In an ideal solution, the composition of the liquid phase and the vapor phase is the same at equilibrium.

Here’s a brief analysis of each mixture:

1. Ethanol + Chloroform:

   • This mixture does not behave ideally due to strong hydrogen bonding interactions between ethanol and chloroform, which can cause deviations from Raoult's Law.

2. Nitric Acid + Water:

   • Nitric acid and water form a non-ideal solution. Nitric acid forms strong hydrogen bonds with water, resulting in significant deviations from ideal behavior. Thus, the composition in the liquid and vapor phases will not be the same.

3. Benzene + Toluene:

   • Benzene and toluene form an ideal solution. The interactions between benzene and toluene are similar, and thus the composition of the liquid and vapor phases will be the same.

4. Ethyl Chloride + Ethyl Bromide:

   • Ethyl chloride and ethyl bromide also form an ideal solution. The interactions between these two similar substances lead to minimal deviations from ideal behavior.

Based on the above analyses, the mixtures that will have the same composition in the liquid and vapor phases are:

2. (iii) and (iv)

So the correct answer is:

2. (iii) and (iv)

The correct answer is Option B.
 
Molal elevation constant is a characteristic constant for a given solvent. It is the elevation of boiling point produced when one mole of solute is dissolved in 1 kg of solvent. The proportionality constant, Kb, is called the molal boiling point elevation constant. It is a constant that is equal to the change in the boiling point for a 1-molal solution of a nonvolatile molecular solute.

The correct answer is Option B.
 
∆T_b =(K_b × 1000 × W₂) / M₂ × W₁
⇒ M₂ = (K_b × 1000 × W₂) / ∆T_b × W₁
= (1.71 × 1000 × 2) / 1 × 100
= 34.2g

The correct answer is option C 
ΔT_f= K_f  x m Since ΔT_f for 5m NaCl will be higher than for 2m, 5m NaCl solution freezes at a lower temperature.

Molality (amount of moles per 1 kg of the solvent, mol/kg) and mole fraction (mol/mol) will remain constant since they are independent of volume of the solution which changes with temperature. Molarity i.e. amount of moles of a substance in 1 liter of a solution will change with volume of the solution so it will change with temperature.

The correct answer is “molal depression constant is high”.

Camphor is used for the determination of molecular masses of solute by Rast method because its molal depression constant is very high 40Kmolality^-1 .