CBSE Class 12 Chemistry Solutions MCQs Set L

Question. Azeotrope mixture are:
(a) mixture of two solids
(b) those will boil at different temperature
(c) those which can be fractionally distilled
(d) constant boiling mixtures
Answer: d

Question. 0.5 M aquous solution of Glucose is isotonic with:
(a) 0.5 M KCl solution
(b) 0.5 M CaCl₂ solution
(c) 0.5 M Urea solution
(d) 1 M solution of sucrose
Answer: c

Question. Which one is the best colligative property for determination of molecular mass of polymer?
(a) osmotic pressure
(b) elevation in boiling point
(c) depression in freezing point
(d) osmosis
Answer: a

Question. Mixing of HNO₃ and HCl is reaction:
(a) endothermic reaction
(b) exothermic reaction
(c) both exothermic and endothermic
(d) depend on entropy of reaction
Answer: b

Question. If Kf value of H₂O is 1.86. The value of ΔTf for 0.1 m solution of non-volatile solute is
(a) 18.6
(b) 0.186
(c) 1.86
(d) 0.0186
Answer: b

Question. Which of the following do not depend on temperature?
(a) % W/V (weight/volume)
(b) molality
(c) molarity
(d) normality
Answer: b

Question. The plant cell will shrink when placed in:
(a) water
(b) A hypotonic solution
(c) a hypertonic solution
(d) an siotonic solution
Answer: c

Question. Which of the following does not show positive deviation from Raoult’s law?
(a) benzone + chlorofor
(b) benzene + acetone
(c) benzene + ethanol
(d) benzene + CCl₄
Answer: a

Question. Henry’s law constant K of CO₂ in water at 25°C is 3 × 10^–2 mol/L atm^–1.Calculation the mass of CO₂ present in 100 L of soft drink bottled with a partial pressure of CO₂ of 4 atm at the same temperatrue.
(a) 5.28 g
(b) 12.0 g
(c) 428 g
(d) 528 g
Answer: d

Question. Benzoic acid dissolved in benzene shows a molecular weight of:
(a) 122
(b) 61
(c) 244
(d) 366
Answer: c

Question. Which condition is not satisfied by an ideal solution?
(a) ΔHmix = 0
(b) ΔVmix = 0
(c) ΔPmix = 0
(d) ΔSmix = 0
Answer: d

 Question. Which of the following solutions would have the highest osmotic pressure:
(a) M/10 NaCl
(b) M/10 Urea
(c) M/10 BaCl₂
(d) M/10 Glucose
Answer: c

Question. The molality of 98% H₂SO₄ (density = 1.8 g/mL) by weight is:
(a) 6 m
(b) 18 m
(c) 10 m
(d) 4 m
Answer: b

Question. The Van’t Hoff factor for 0.1 M Ba(NO₃)₂ solution is 2.74. The degree of dissociation is:
(a) 91.3%
(b) 87%
(c) 100%
(d) 74%
Answer: b

Question. The freezing point of 11% aquous solution of calcium nitrate will be:
(a) 0°C
(b) above 0°C
(c) 1°C
(d) below 0°C
Answer: d

Question. Solution showing (+) ve deviation from Raoult’s law include:
(a) acetone + CS₂
(b) acetone + C₂H₅OH
(c) acetone + Benzene
(d) acetone + aniline
Answer: a,b

Question. Van’t Hoff factor for a dilute solution of a K₂[HgI₄] is:
(a) 2
(b) 1
(c) 3
(d) zero
Answer: c

Question.Solute when dissolve in water
(a) increases the vapour pressure of water
(b) decreases the boiling point of water
(c) decrease the freezing point of water
(d) All of the above
Answer: d

Question. Which solution will have least vapour pressure?
(a) 0.1 M BaCl₂
(b) 0.1 M Uxa
(c) 0.1 M Na₂SO₄
(d) 0.1 M Na₃PO₄
Answer: d

Question. Which of the following is true for Henry’s constant
(a) It decreases with temperature
(b) It increases with temperature
(c) Independent on temperature
(d) It do not depend on nature of gases.
Answer: d

 Question. 6% (W/V) solution of urea will be isotonic with:
(a) 18% (W/V) solution of glucose
(b) 0.5 M solution of NaCl
(c) 1 M solution of CH₃COOH
(d) 6% (W/V) solution of sucrose.
Answer: a,b,c

Question. The most likely on ideal solution is:
(a) NaCl—H₂O
(b) C₂H₅OH—C₆H₆
(c) C₇H₁₆—H₂O
(d) C₇H₁₆—C₈H₁₈
Answer: d

 VERY SHORT ANSWER TYPE QUESTIONS

Question. What is van’t Hoff factor ? How is it related with :
(a) degree of dissociation (b) degree of association
Answer. (a) α = i – 1/n – 1 (b) α = i – 1/1/n – 1

Question. Why NaCl is used to clear snow from roads ?
Answer. It lowers freezing point of water.

Question. Henry law constant for two gases are 21.5 and 49.5 atm, which gas is more soluble ?
Answer. KH is inversely proportional to solubility.

 Question. What role does the molecular interaction play in solution containing chloroform and acetone ?
Answer. H-bonding formed, results in negative deviation from Raoult’s law.

Question. What is the effect on boiling and freezing point of a solution on addition of NaCl ?
Answer. Boiling point increases and freezing point decreases.

Question. What is the Van’t Hoff factor in K₄[Fe(CN)₆] and BaCl₂ ?
Answer. 5 and 3

Question. Why the molecular mass becomes abnormal ?
Answer. Due to association or dissociation of solute in given solvent.

Question. Why water cannot be completely separated from aqueous solution of ethyl alcohol ?
Answer. Due to formation of azeotrope at (95.4%).

Question. Why anhydrous salts like NaCl or CaCl₂ are used to clear snow from roads on hills ?
Answer. They depress freezing point of water.

Question. What is Van’t Hoff factor ?
Answer. It is the ratio of normal molecular mass to observed molecular mass. It is denoted as i.
i = normal molecular mass/observed molecular mass
= no. of particles after association or dissociation/no. of particles before dissociation or association

Question. Why the boiling point of solution is higher than pure liquid ?
Answer. Due to lowering in vapour pressure.

Question. Liquid A and B on mixing produce a warm solution. Which type of deviation does this solution show ?
Answer. – ve deviations

Question. Give an example of a compound in which hydrogen bonding results in the formation of a dimer.
Answer. Carboxylic acids or other example

Question. Why osmotic pressure is considered as colligative property ?
Answer. It depends upon number of moles of solute present in solution.

Question. What role does the molecular interaction play in the solution of alcohol and water ?
Answer. Positive deviation from ideal behaviour.

Fill in the blanks type:

Question. The property which depends on number of particles of solute is called ………….
Answer: Colligative property

Question. Azeotrope mixture cannot be separate by ………….
Answer: Fractional distillation

Question. Match the column and choose correct option Vant’Hoff factor Behaviour of compound
(A) i = 1 P. Impossible
(B) i > 1 Q. Association is the solution
(C) i < 1 R. Dissociation in the solution
(D) i = 0 S. No dissociation or association
(a) A–S, B–R, C–P, D–Q
(b) A–R, B–S, C–Q, D–P
(c) A–S, B–P, C–R, D–Q
(d) A–S, B–R, C–Q, D–P
Answer: d

SHORT ANSWER TYPE QUESTIONS

Question. Define reverse osmosis. Write its one use.
Answer: Desalination of water.

Question. Why does an azeotropic mixture distills without any change in composition ?
Answer. It has same composition of components in liquid and vapour phase.

Question. Why is it advised to add ethylene glycol to water in a car radiator in hill station ?
Answer. Anti-freeze.

Question. Why is liquid ammonia bottle first cooled in ice before opening it ?
Answer. At room temperature, the vapour pressure of liquid ammonia is very high. On cooling vapour pressure decreases, therefore the liquid ammonia will not splash out.

Question. Which colligative property is preferred for the molar mass determination of macromolecules ?
Answer. Osmotic pressure measurement is preferred for molar mass determination because :
(a) even in dilute solution the osmotic pressure values are appreciably high and can be measured accurately.
(b) osmotic pressure can be measured at room temperature.

Question. The dissolution of ammonium chloride in water is endothermic process.What is the effect of temperature on its solubility ?
Answer. Since dissolution of NH4Cl in water is endothermic process, its solubility increases with rise in temperature (i.e., Le-Chatelier process).

Question. Two liquids A and B boil at 145ºC and 190ºC respectively. Which of them has higher vapour pressure at 80ºC ?
Answer. Lower the boiling point more volatile is the respective compound. Therefore, liquid A will have higher vapour pressure at 80ºC.

Question.How many grams of KCl should be added to 1 kg of water to lower its freezing point to – 8.0ºC ? (Kf = 1.86 K kg/mol)
Answer. Since KCl dissociate in water completely, i = 2.

Question. Calculate the molarity of pure water (d = 1 g mL^–1).
Answer. Desity of water = 1 g mL^–1
Mass of 1000 ml of water = V × d
= 1000 mL × 1 gm^–1
= 1000 g
Moles of water = 1000/18
= 55.55 mol
Now, mole of H₂O present in 1000 mL or 1 L of water.
So, molarity = 55.55M

SHORT ANSWER-II TYPE QUESTIONS 

Question. Suggest the most important type of intermolecular attractive interaction in the following pairs :
(a) n-hexane and n-octane (b) I₂ and CCl₄
(c) NaClO₄ and water
Answer. (a) Vander Waals interaction
(b) Vander Waals interaction
(c) Ion-dipole interaction

Question. A solution of glycerol (C₃H₈O₃) in water was prepared by dissolving some glycerol in 500 g of water. This solution has a boiling point of 100.42ºC while pure water boils at 100ºC. What mass of glycerol was dissolved to make the solution ? (K_b = 0.512 K kg mol^-1)
Answer. 37.73 g

Question. 18 g of glucose (C₆H₁₂O₆) (molar mass = 180 g mol^-1) is dissolved in 1 kg of water in a sauce pan. At what temperature will this solution boil ? (K_b for water = 0.52 K kg mol^-1, boiling point of pure water = 373.1 K)
Answer. 373.202 K