# Physical Chemistry Class -12 Chapter-2 Solution Most VVI Subjective Questions

Ans:– Osmosis is the phenomenon of a spontaneous flow of the solvent molecules through a semipermeable membrane from pure solvent to solution or from a dilute solution to concentrated solution.

Q.3. What is ideal and non-ideal solution ?

Ans:- Ideal Solution:- An ideal solution is that solution in which each component obeys Raoult’s law under all conditions of temperature and concentrations.

An ideal solution will satisfy the following conditions  :

(i) There will be no change in volume on mixing the two components.

(ii) There will no change in enthalpy when two components are mixed.

Non-ideal solution:- A solution which does not obey Raoult’s law is called non-ideal solution.

For example, when we mix sulfuric acid (solute) in water (solvent) the amount of heat generated is very large and a change in volume is also observed. This is due to formation of a non-ideal solution.

Q.4. Why does Vapour pressure of a liquid decreases with addition of a non volatile solid solute ?

Ans:– The vapour pressure of a liquid decreases with addition of a non volatile solid solute because some molecules of the  solvent on the surface are replaced by the molecules of the solute.

Q.5. How is molarity of a solution different from molality ?

Ans:- Molarity is the defined as the number of moles of solute is dissolved in 1 litre of solution.

Molarity(M) = moles of solute/volume of solution in litre

Molality is defined as the number of moles of solute dissolved in 1 kg of solvent.

Molality = Moles of solute/Mass of the solvent in kg

Q.6. Define Raoult’s law ?

Ans:- Vapour pressure of a liquid component in a solution is directly proportional to mole fraction of the liquid in liquid phase.

Q.7. State colligative properties of dilute solution. Write down the different types of colligative properties.

Ans:- The property, which depends upon number of atom or molecule of the solute and hot on their nature is called colligative properties. There are four types of colligative properties.

(i) Relative lowering of vapour pressure

(ii) Elevation in boiling point

(iii) Depression in freezing point

(iv) osmosis or osmotic pressure

Q.8. What is semipermeable membrane ?

Ans:- The membrane which allows the solvent molecules, but not the solute molecules, to pass through it is called Semipermeable membrane.

Q.9. What do you mean by vapour pressure ? What happens to the vapour pressure, when (i) Volatile solute is dissolved in solution, (ii) non volatile solute is dissolved in solution ?

Ans:- Vapour pressure due to vapour of a liquid at a given temperature at equilibrium when rate of evaporation and condensation becomes equal. (i) Volatile solute increases vapour pressure of solvent. (ii) non volatile solute lowers vapour pressure of solvent.

Q.10. 4 gram of caustic soda (molar mass = 40) is dissolved in water and solution is made of 200 cm³. Calculate the molarity of solution.

Ans:- M = moles of solute/Volume of solution (in L)

0.1mol/0.2L = 0.5 mol L⁻¹ = 0.5 M