Chemistry Class 12 NCERT Solutions: Chapter 2 Solutions Part 5

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Exercise: 2

Q: 1. Define the term solution. How many types of solutions are formed? Write briefly about each type with an example.

Answer:

Homogeneous mixtures of two or more than two components are known as solutions.

There are three types of solutions.

(i) Gaseous solution:

The solution in which the solvent is a gas is called a gaseous solution. In these solutions, the solute may be liquid, solid, or gas. For example, a mixture of oxygen and nitrogen gas is a gaseous solution.

(ii) Liquid solution:

The solution in which the solvent is a liquid is known as a liquid solution. The solute in these solutions may be gas, liquid, or solid. For example, a solution of ethanol in water is a liquid solution.

(iii) Solid solution:

The solution in which the solvent is a solid is known as a solid solution. The solute may be gas, liquid or solid. For example, a solution of copper in gold is a solid solution.

Q: 2. Give an example of solid solution in which the solute is a gas.

Answer :

In case a solid solution is formed between two substances (one having very large particles and the other having very small particles), an interstitial solid solution will be formed. For example, a solution of hydrogen in palladium is a solid solution in which the solute is a gas.

Q3: Define the following terms:

(i) Mole fraction

(ii) Molality

(iii) Molarity

(iv) Mass percentage.

Answer :

(i) Mole fraction:

The mole fraction of a component in a mixture is defined as the ratio of the number of moles of the component to the total number of moles of all the components in the mixture.

Mole fraction of a component

Mole fraction is denoted by

If in a binary solution, the number of moles of the solute and the solvent are respectively, then the mole fraction of the solute in the solution is given by,

Similarly, the mole fraction of the solvent in the solution is given as:

(ii) Molality:

Molality (m) is defined as the number of moles of the solute per kilogram of the solvent. It is expressed as:

Molality (m)

(iii) Molarity:

Molarity (M) is defined as the number of moles of the solute dissolved in one Litre of the solution. It is expressed as:

Molarity (M)

(iv) Mass Percentage:

The mass percentage of a component of a solution is defined as the mass of the solute in grams present in 100 g of the solution. It is expressed as:

Mass % of a component

Q: 4. Concentrated nitric acid used in laboratory work is nitric acid by mass in aqueous solution. What should be the molarity of such a sample of the acid if the density of the solution is ?

Molar mass of nitric acid

Then, number of moles of

Given Density of solution

solution

Molarity of solution