Solutions Exam Questions Class 12 Chemistry

Please see Chapter 2 Solutions Exam Questions Class 12 Chemistry below. These important questions with solutions have been prepared based on the latest examination guidelines and syllabus issued by CBSE, NCERT, and KVS. We have provided Class 12 Chemistry Questions and answers for all chapters in your NCERT Book for Class 12 Chemistry. These solved problems for Solutions in Class 12 Chemistry will help you to score more marks in upcoming examinations.

Exam Questions Chapter 2 Solutions Class 12 Chemistry

MULTIPLE CHOICE QUESTIONS

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

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

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

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

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%

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

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

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

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

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

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

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.

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

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

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

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

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

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

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

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.

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

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

Fill in the blanks type:

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

Question. Azeotrope mixture cannot be separate by ………….

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

VERY SHORT ANSWER TYPE QUESTIONS

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

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

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. Calculate the volume of 75% of H₂SO₄ by weight (d = 1.8 gm/ml) required to prepare 1 L of 0.2 M solution.
Answer.

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

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

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. 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.

SHORT ANSWER TYPE QUESTIONS

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. 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. An aqueous solution of 2% non-volatile exerts a pressure of 1.004 Bar at the normal boiling point of the solvent. What is the molar mass of the solute ?
Answer.

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

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

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. 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.

SHORT ANSWER-II TYPE QUESTIONS 

Question. 1. Determine the amount of CaCl₂ dissolved in 2.5L at 27ºC such that its osmotic pressure is 0.75 atm at 27ºC. (i for CaCl2 = 2.47)
Answer.*

Question. Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K₂SO₄ in 2 litre of water at 25ºC assuming that it is completely dissociated.
Answer. If K₂SO₄ is completely dissociated,

Question. If the solubility product of CuS is 6 × 10^-16, calculate the maximum molarity of CuS in aqueous solution.
Answer. Ksp of CuS = 6 × 10^-16
If S is the solubility, then
CuS → Cu²⁺ + S^2-
[Cu²⁺] = S, [S^2-] = S
K_sp = [Cu²⁺][S^2-]
= S × S = S²

= 2.45 × 10⁻⁸ M
Highest molarity = 2.45 × 10⁻⁸ M

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. The vapour pressure of water is 12.3 Kpa at 300K. Calculate vapour pressure of 1 molal solution of a non-volatile solute in it.
Answer.

Question. 6.90M solution of KOH in water contains 30% by mass of KOH. Calculate the density of the KOH solution. (Molar mass of KOH = 56 g mol^-1)
Answer. Mass of KOH = 30 g

Question. An anti-freeze solution is prepared from 222.6 g of ethylene glycol C₂H₄(OH)₂ and 200 g of water. Calculate the molality of the solution. If the density of this solution be 1.072 g mL^-1, what will be the molarity of the solution ?
Answer.

Question. What would be the molar mass of compound if 6.21 g of it is dissolved in 24.0 g of CHCl₃ from a solution that has a boiling point of 68.04ºC. The boiling point of pure chloroform is 61.7ºC and the boiling point elevation constant K_b for chloroform is 3.63ºC/m.
Answer. Elevation in boiling point ΔT_b = 68.04 – 61.7 = 6.31ºC
Mass of substance W_B = 6.21 g
Mass of CHCl₃ W_A = 24.0 g
K_B = 3.63 ºC/m

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

LONG ANSWER TYPE QUESTIONS 

Question. (a) Define Raoult’s law of binary solution containing non-volatile solute in it.
(b) On dissolving 3.24 g of sulphur in 40 g of benzene, boiling point of solution was higher than that of benzene by 0.81K (Kb = 2.53 K kg mol^-1). What is molecular formula of sulphur ? (Atomic mass s = 32 g mol^-1)
Answer. (a) At a given temperature, the vapour pressure of a solution containing non-volatile solute is directly proportional to the mole fraction of the solvent.

Let the molecular formula of sulphur = S_x
Atomic mass of sulphur = 32
Molecular mass = 32 × x
32x = 253
x = 7.91 ≈ 8
Molecular formula of sulphur = S8

Question. (a) Outer shells of two eggs are removed. One of the egg is placed in pure water and the other is placed in saturated solution of NaCl. What will be observed and why ?
(b) A solution prepared by dissolving 8.95 mg of a gene fragment in 35.0 ml of water has an osmotic pressure of 0.335 ton at 25ºC. Assuming the gene fragment is a non-electrolyse, determine the molar mass.
Answer. (a) In pure water the egg swells and in saturated solution of NaCl it will shrinks.
(b) Mass of gene fragment = 8.95 mg
= 8.95 × 10^-3 g
Volume of water = 35.0 ml = 35 × 10^-3 L
π = 0.335 ton = 0.335/760 atm
Temp = 25 + 273 = 298 K

Question. (a) Define van’t Hoff factor.
(b) Calculate the freezing point depression expected for 0.0711M aqueous solution of Na₂SO₄. If this solution actually freezes at – 0.320ºC, what would be the value of van’t Hoff factor ? (Kf = 1.86ºC mol^-1)
Answer. (a) Van’t Hoff factor : It is the ratio of the normal molar mass to the observed molar mass of the solute.
(b) ΔTf = Kf × M
ΔTf = 1.86 × 0.0711 = 0.132
Observed freezing point = 0 – (– 0.320) = 0.320ºC

Question. (a) What is the value of i when solute is associated and dissociated ?
(b) Calculate the freezing point of an aqueous solution containing 10.50 g of MgBr₂ in 200 g of water. (Molar mass of MgBr₂ = 184, Kf = 1.86 K kg mol^-1)
Answer. (a) i < 1 when solute is associated and
i > 1 when solute is dissociated.

Question. (a) What is the value of i for Al₂(SO₄)₃ when it is completely dissociated ?
(b) Calculate the boiling point of a solution prepared by adding 15.00 g of NaCl to 250 g of water. (Kb = 0.512 K kg mol^-1 and molar mass of NaCl = 58.44 g mol^-1)
Answer.