Important Questions Class 12 Chemistry Chapter 2 Solutions 1 Mark Questions

1. Define the term –solubility?

Ans. The maximum amount of a substance that can be dissolved in a specified amount of solvent is called its solubility.

2. What is the effect of pressure on solubility of a gas?

Ans. The solubility of a gas increases with increases of pressure.

3. State Henry’s Law.

Ans. Henry’s Law states that at a constant temperature the solubility of a gas in a liquid is directly proportional to the pressure of the gas.

4. State Raoult’s Law.

Ans. Raoult’s Law states that for a solution of volatile liquids, the partial vapour pressure of each component in the solution is directly proportional to its mole fraction.

5. What are the factors on which vapour pressure depends?

Ans. The factors on which vapour pressure depends are –

1) Temperature of the liquid.       2) Nature of the liquid.

6. The vapour pressure of solvent gets lowered, when a non- volatile solute is added to it. Why?

Ans. When a non-volatile solute is added to a solvent, the surface area for escape of solvent molecules decreases and vapour pressure gets lowered.

7. Name two ways by which vapour pressure of a liquid can be lowered.

Ans. The two ways by which vapour pressure can be lowered are –

1) By decreasing the temperature.

2) By adding a non- volatile solute.

8. Define‘solution’?

Ans. Solutions are homogeneous mixtures of two or more than two components.

9. Define the following terms : (a) Molality (b) Molarity

Ans. (a) Molality is defined as the number of moles of the solute per kilogram of solvent.

(b) Molarity (M) = Number of moles of solute dissolved in one litre of solution.

10. How does change in temperature changes the molarity and molality values?  

Ans. As the temperature increases, volume increases and molarity decreases whereas molality does not change with any change in temperature.

11. Define the term colligative properties?

Ans. The properties which depends upon amount of solute and not upon the nature of solute are called colligative properties.

12. What are the possible deviations from ideal behaviors?

Ans. There are two types of deviation from ideal behaviour – positive and negative deviations.

13. Give one example of each deviation?

Ans. Positive deviation – ethanol and acetone.

Negative deviation – chloroform and acetone.

14. At , the vapour pressure of water is 55.3 mm Hg .Calculate the vapour pressure at the same temperature over 10% aqueous solution of urea?

Ans. 53.48 mm Hg.

15. How much urea (molar mass 60 g/mol) should be dissolved in 50g of water so that its vapour pressure at room temperature is reduced by 25%?

Ans. 41.7 g .

16. Why is the boiling point elevated when a non – volatile solute is dissolved in a liquid?

Ans. When a non – volatile solute is added the vapour pressure decreases and the solution is heated to a higher temperature, increasing the boiling point.

17. How is boiling point changed when mass of solvent is doubled?

Ans

= when the amount of solvent is doubled, ∆Tbis halved.

18. What happens when red blood cells are placed in 0.1% NaCl solution?

Ans. Water from NaCl solution passes into cells &they swell. Finally they will burst.

19. How is osmotic pressure of a solution related to its concentration?

Ans. Osmotic pressure, π = CRT

C = concentration, R = gas constant, T= temperature

20. Calculate the osmotic pressure of 0.25 M solution of urea at. R = 0.083 L bar/mol/k.

Ans. T =  = 310k

 RT

= 6.43 bar.

21. An aqueous solution of glucose, has osmotic pressure of 2.72 atm at 298k. How many moles of glucose were dissolved per litre of solution?

Ans. 0.111 mol.

22. When does the measurement of colligative property leads to abnormal molecular mass?

Ans. When the solute undergoes either association or disassociation abnormal molar mass is obtained.

23. When is the value of i less then unity?

Ans. When the solute under goes association in solution, I is less then unity.

24. The molecular mass of a solute is 120 g/mol and van’t Hoff factor is 4. What is its abnormal molecular mass?

Ans. Abnormal molecular mass

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