NCERT Questions for Class 12 Chemistry Chapter 1 – Solutions

Important Questions with Solutions of Class 12 Chemistry Chapter 1 – Solutions

1) Adding HgI₂ to KI (aq.) elevates vapor pressure. State the reason!

Ans – Vapor pressure is the colligative feature based on the no. of particles available in the solution. When HgI₂ is added to KI, they create a model by reducing the no. of solute elements. Thus, the vapor pressure will begin to rise.

2) What would be the boiling point of the solution obtained by combining 2 miscible liquids that deviate negatively according to Raoult’s law?

Ans – Based on Raoult’s law, when 2 miscible liquids depict negative deviation when a solution is formed post-mixing, the vapor pressure decreases by raising its boiling point.

3) Give an illustration of a solution that is “liquid in solid” form.

Ans – Liquid in solid signifies that the solute will be liquid and the solvent will be solid. Mercury in sodium (amalgam) is one example.

4) Describe the following:

(a) Find thesolubility of a solid in a liquid with a dynamic equilibrium.

Ans – The maximum solute dissolved in a liquid solvent is called solubility. If additional solute is present, the dissolved solute will start precipitating creating a dynamic equilibrium.

(b) Why do Ionic elements remain soluble in water but insoluble in nonpolar solvents?

Ans – We understand the base rule of ‘like dissolves like.’ In this case, the ionic elements are polar-based molecules & are soluble in water as it is also naturally polar.

5) There will be an increase in boiling point when 1 mole of NaCl is mixed with 1 litre of water. But, when 1 mole of CH₃OH gets combined with 1 litre of water, there will be a considerable reduction in boiling point. Why?

Ans – Assume if NaCl (non-volatile solute) & water is mixed, there is a decrease in vapor pressure by raising the boiling point. Meanwhile, CH₃OH is highly volatile compared to water (i.e., It has a larger vapor pressure than water reducing the boiling point).

6) Explain that the relative reduction in solvent vapor pressure is a colligative feature.

Ans – Colligative features are based on the solute particles in the solution. For accurate outcomes, it’s the ratio of solute particles with solvent particles available in the solution.

As we know, the relative reducing vapor pressure can be,

Meanwhile, Raoult’s law represents,

Where ‘x’ is the mole fraction

Therefore, the relative lowering of the solvent’s vapor pressure is a colligative property.

7) What’s the relative lowering in vapor pressure compared to the depression freezing point & elevation in boiling point?

Ans – The relative reduction in vapor pressure, depression in freezing point & increase in boiling point are the solution-based colligative features. These properties are based on the dissolved solute elements in a solvent.

Hence, if there is a change in vapor pressure due to the addition of a non-volatile solute into the solvent, the rest of the features will also get altered. The relative vapor pressure reduction of the solute enables depression in the freezing point & increases the boiling point.

8) Explain the following: –

(a) CaCl₂ can remove snow from roads in hill stations.

Ans: Calcium chloride is accountable for depression in the freezing point of water around a certain extent from where it can’t form a block of ice. So, it helps remove the snow from roads.

(b) Ethylene glycol can act as an antifreeze component in vehicle radiators of cold countries.

Ans: Adding ethylene glycol to car radiators can reduce the water freezing point & eliminate the line bursting during cold winters.

(c) The freezing point depression of 0.01 m NaCl is almost twice of 0.01 m glucose solution.

Ans: The sodium chloride combines in the solution providing 2 ions & glucose won’t link to form ions. Hence, the relationship of freezing point depression is denoted as,

△T_t = iK_tm

NaCl consists of almost double the depression in the freezing zone compared to glucose despite having similar concentrations.

9) For a dilute solution with 2.5 g of a non-volatile &  non-electrolyte solute in 100 gms of water, the increase in boiling point at 1 atm pressure will be 2°C. Considering the solute concentration is less than the solvent’s, find the solution’s vapor pressure (mm of Hg). [Given: K_b for water = 0.76Kkgmol^-1]

Ans – As we know,

W₂ = 2.5g

W₁ = 100g

ΔT_b = 2°C

P° = 1 atm = 760mm Hg

K_b =0.76 Kkgmol^-1

M1 =18gmol^-1

Now, the increase in boiling point will be;

⇒ M₂ = 9.5gmol^-1

Meanwhile, for dilute solutions;

Therefore, the vapor pressure of the solution will be P_s =724mmHg.