Full Chapter Question Paper Chapter Solutions
Full Chapter Question Paper Chapter Solutions
CLASS – XII
MM:70 Time: 3 hours
(Chapter – Solution)
Full Chapter Question Paper Chapter Solutions
General Instructions: Read the following instructions carefully.
a) There are 35 questions in this question paper with internal choice.
b) SECTION A consists of 18 multiple-choice questions carrying 1 mark each.
c) SECTION B consists of 7 very short answer questions carrying 2 marks each.
d) SECTION C consists of 5 short answer questions carrying 3 marks each.
e) SECTION D consists of 2 case- based questions carrying 4 marks each.
f) SECTION E consists of 3 long answer questions carrying 5 marks each.
g) All questions are compulsory.
h) Use of log tables and calculators is not allowed
SECTION – A
The following questions are multiple-choice questions with one correct answer. Each question carries 1 mark. There is no internal choice in this section.
MULTIPLE CHOICE QUESTIONS:
1. The value of Henry’s constant KH is:
(a) Greater for gases with higher solubility
(b) Greater for gases with lower solubility.
(c) Constant for all gases.
(d) Not related to the solubility of gases.
2. Increasing the temperature of an aqueous solution will cause:
(a) Decrease in molality
(b) Decrease in molarity
(c) Decrease in mole fraction
(d) Decrease in % (w/w)
3. Colligative properties depend on:
(a) The nature of the solute
(b) The number of solute particles in solution
(c) The physical properties of solute
(d) The nature of the solvent
4. The unit of ebullioscopic constant is:
(a) K kg mol-1
(b) K-1 kg mol
(c) K kg-1 mol-1
(d) K kg-1 mol
5. The most suitable colligative property to determine the molecular weight of biomolecules is:
(a) Lowering of vapour pressure
(b) Osmotic pressure
(c) Elevation of boiling point
(d) Depression of freezing point
6. The number of moles of NaCl in 3 litres of 3 M solution is:
(a) 1
(b) 3
(c) 9
(d) 7
7. Which has the highest freezing point:
(a) 1 M Glucose
(b) 1 M NaCl
(c) 1 M CaCl2
(d) 1 M AlF3
8. Which of the following conditions is not satisfied by an ideal solution?
(a) ΔHmixing = 0
(b) ΔVmixing = 0
(c) Raoult’s Law is obeyed
(d) Formation of an azeotropic mixture
9. Considering the formation, breaking, and strength of hydrogen bonds, predict which of the following mixtures will show a negative deviation from Raoult’s law?
(a) Methanol and acetone.
(b) Chloroform and acetone.
(c) Phenol and aniline.
(d) Cyclohexane and ethanol
10. The boiling point of an azeotropic mixture of water and ethanol is less than that of water and ethanol. The mixture shows:
(a) No deviation from Raoult’s Law.
(b) Positive deviation from Raoult’s Law.
(c) Negative deviation from Raoult’s Law.
(d) That the solution is unsaturated.
11. If 2 gm of NaOH is present in 200 mL of its solution, its molarity will be:
(a) 0.25
(b) 0.5
(c) 5
(d) 10
12. Atmospheric pollution is generally measured in the units of:
(a) Mass percentage
(b) Volume percentage
(c) Volume fraction
(d) ppm
13. A 5% solution of cane sugar (molecular mass = 342) is isotonic with a 1% solution of substance A. The molecular weight of X is:
(a) 342
(b) 171.2
(c) 68.4
(d) 136.8
14. 234.2 gm of sugar syrup contains 34.2 gm of sugar. What is the molal concentration of the solution?
(a) 0.1
(b) 0.5
(c) 5.5
(d) 55
15. Given below are two statements labelled as Assertion (A) and Reason (R)
Assertion (A): When NaCl is added to water, a depression in freezing point is observed.
Reason (R): The lowering of vapour pressure of a solution causes depression in the freezing point.
Select the most appropriate answer from the options given below:
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
16. Given below are two statements labelled as Assertion (A) and Reason (R)
Assertion (A): Azeotropic mixtures are formed only by non-ideal solutions, and they may have boiling points either greater than both the components or less than both the components.
Reason (R): The composition of the vapour phase is the same as that of the liquid phase of an azeotropic mixture.
Select the most appropriate answer from the options given below:
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
17. Given below are two statements labelled as Assertion (A) and Reason (R)
Assertion (A): Molarity of a solution in liquid state changes with temperature.
Reason (R): The volume of a solution changes with a change in temperature.
Select the most appropriate answer from the options given below:
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
18. Given below are two statements labelled as Assertion (A) and Reason (R)
Assertion (A): Molecular mass of benzoic acid when determined by colligative properties is found high.
Reason (R): Dimerization of benzoic acid.
Select the most appropriate answer from the options given below:
(a) Both A and R are true, and R is the correct explanation of A
(b) Both A and R are true, but R is not the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true
Full Chapter Question Paper Chapter Solutions
SECTION-B
This section contains 7 questions with internal choice in two questions. The following questions are very short answer type and carry 2 marks each.
19. Equimolal solutions of NaCl and BaCl2 are prepared in water. The freezing point of NaCl is found to be – 20°C. What freezing point do you expect for BaCl2 solution?
20. Write down four important points of difference between an ideal and a non-ideal solution.
OR
Calculate the mole fraction of benzene in a solution containing 30% by mass of it in CCl4.
21. What do you mean by Raoult’s law? What are the limitations of Raoult’s law?
OR
How many types of azeotropes are there? Define them along with one example of each.
22. Plot a graph between vapour pressure and mole fraction of a solution obeying Raoult’s Law at constant temperature.
23. A mixture of chlorobenzene and bromobenzene is nearly an ideal solution, but a mixture of chloroform and acetone is not. Explain.
24. What is the molality of a 1.0 M solution of sodium nitrate (NaNO3) if its density is 1.25 g cm-3?
25. The vapour pressure of water is 12.3 kPa at 300K; calculate the vapour pressure of a 1 molar solution of a solute in it.
SECTION-C
This section contains 5 questions with internal choice in two questions. The following questions are short answer type and carry 3 marks each.
26. Miscible liquid pairs often show positive and negative deviation from Raoult’s law. Explain the reason for such deviation. Give one example of each of liquid pairs.
27. A solution containing 18 g of non-volatile solute in 200g of water freezes at 272.07 K. Calculate the molecular mass of solute (given Kf = 1.86 K/m)
OR
Calculate the osmotic pressure at 270C of a solution formed by mixing equal volumes of two solutions, one containing 0.05 mole of glucose in 250 ml of solution and the other containing 3.42 g of C12H22O11 in 250 ml of solution. [R = 0.082 L atm mol-1K-1]
28. An aqueous solution freezes at 272.4 K while pure water freezes at 273 K. Determine
(i) Molality of solution.
(ii) Boiling point of solution
(iii) Lowering of vapour pressure of water at 298 K.
29. The elements A and B formed purely covalent compounds having molecular formula AB2 and AB4. When dissolved in 20 grams of benzene, 1 gram of AB2 lowers the freezing point by 2.3 K and that of AB4 by 1.3 K. Calculate the atomic mass of A and B. The molar depression constant for freezing is 5.1 K kg mol-1
30. An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute? (Vapour pressure of pure water at the boiling point (P0) = 1 atm = 1.013 bar)
Full Chapter Question Paper Chapter Solutions
SECTION-D
The following questions are case-based. Each question has an internal choice and carries 4 (1+1+2) marks each. Read the passage carefully and answer the questions that follow.
31. Osmotic pressure results from a reduction in the chemical potential of a solvent in the presence of a solute. The tendency of a system to have equal chemical potentials over its entire volume and to reach a state of lowest free energy gives rise to the osmotic diffusion of matter. In ideal and dilute solutions, the osmotic pressure is independent of the nature of the solvent and solutes. At constant temperature, it is determined only by the number of kinetically active particles, ions, molecules, associated species, and colloidal particles in a unit volume of the solution. For very dilute solutions of non-dissociating compounds, osmotic pressure is described with sufficient accuracy by the equation πV = nRT, where n is the number of moles of solute, V is the volume of the solution, R is the universal gas constant, and T is the absolute temperature. The following questions are multiple-choice questions. Choose the most appropriate answer
(i) Name and define the process/method which is used for purification of water?
(ii) Which colligative property is most suitable to measure the molecular mass of proteins and why?
(iii) 200 cm3 of an aqueous solution of a protein contains 1.26 g of the protein. The osmotic pressure of such a solution at 300 K is found to be 2.57 × 10-3 bar. Calculate the molar mass of the protein.
OR
A solution contains 0.8960g of K2SO4 in 500ml solution. Its osmotic pressure is found to be 0.690atm at 270C. Calculate the value of Van’t Hoff factor. (K = 39.0, S = 32, O = 16, R = 0.082atm mol-1K-1).
32. Read the passage carefully and answer the questions that follow.
A solution which obeys Raoult’s Law strictly is called an ideal solution, while a solution that shows deviation from Raoult’s Law is called a non-ideal solution or real solution. Suppose the molecules of the solvent and solute are represented by A & B, respectively, and let AB, AA, and BB be the attractive forces between A-B, A-A, and B-B, respectively. An ideal solution of compound A&B is defined as the solution in which the intermolecular interactions between the compounds A and B are of the same magnitude as the intermolecular interactions found in the pure components AA and BB. Similarly, a non-ideal solution of the components A and B is defined as a solution in which the intermolecular interactions between the components A and B are of a different magnitude than the intermolecular interactions found in the pure components AA and BB.
(i) What type of liquids form the ideal solution?
(ii) Give one example of an ideal solution.
(iii) (a) Write two characteristics of a non-ideal solution.
(b) Which type of deviation will be shown by the solution if AB < AA?
OR
Plot a graph between vapour pressure and mole fraction of a non-ideal solution showing positive and negative deviations from an ideal solution.
SECTION – E
The following questions are long answer type and carry 5 marks each. Two questions have an internal choice.
33. (i) Two liquids A and B, on mixing, form an ideal solution. At 300C vapour pressure of a solution containing 3 mol of A and 1 mol of B is 550 mmHg. But when 4 mol of A and 1 mol of B are mixed. The vapour pressure of the solution thus formed is 560 mm Hg. What would be the V.P of pure A and B?
(ii) Explain the fact that Raoult’s Law is a special case of Henry’s Law.
(iii) According to Raoult’s law, the vapour pressure of a volatile component in a given solution is given by pi = xi pi0.
OR
(a) 0.6 mL of acetic acid (CH3COOH), having density 1.06 g mL–1, is dissolved in 1 litre of water. The depression in freezing point observed for this strength of acid was 0.0205°C. Calculate the van’t Hoff factor and the dissociation constant of the acid.
(b) Define Van’t Hoff factor. Give the value of Van’t Hoff factor in case of the following: Association, dissociation, and neither association nor dissociation of solute when dissolved in a solvent.
34. (a) What is meant by abnormal molar mass of solute? Discuss the factors which bring abnormality in the experimentally determined molecular masses of solutes using colligative properties.
(b) If N2 gas is bubbled through water at 293 K, how many millimoles of N2 gas would dissolve in 1 litre of water? Assume that N2 exerts a partial pressure of 0.987 bar. Given that Henry’s law constant for N2 at 293 K is 76.48 kbar.
l Molar Mass/ van’t Hoff factor = 120/4 = 30 g/mol
35. (a) Why is glycol and water mixture used in car radiators in cold countries? (b) Give a reason: When 30 ml of ethyl alcohol and 30 ml of water are mixed, the volume of the resulting solution is more than 60 ml.
(c) Define cryoscopic constant?
(d) State (i) Azeotropes and (ii) Henry’s Law constant.
Full Chapter Question Paper Chapter Solutions
