CBSE Class 12 Chemistry Solutions Worksheet

Important Questions for NCERT Class 12 Chemistry Solutions 

Question. What is the molarity of H₂SO₄ solution, that has a density 1.84 g/cc at 35°C and contains 98% by weight?
(a) 18.4 M
(b) 18 M
(c) 4.18 M
(d) 8.14 M 

Answer : A

Question. The concentration unit, independent of temperature, would be
(a) normality
(b) weight volume percent
(c) molality
(d) molarity. 

Answer : C

Question. How many grams of CH₃OH should be added to water to prepare 150 mL solution of 2 M CH³OH?
(a) 9.6 × 10³
(b) 2.4 × 10³
(c) 9.6
(d) 2.4

Answer : C

Question. In water saturated air, the mole fraction of water vapour is 0.02. If the total pressure of the saturated air is 1.2 atm, the partial pressure of dry air is
(a) 1.18 atm
(b) 1.76 atm
(c) 1.176 atm
(d) 0.98 atm.

Answer : C

Question. The vapour pressure of two liquids P and Q are 80 and 60 torr, respectively. The total vapour pressure of solution obtained by mixing 3 mole of P and 2 mol of Q would be
(a) 72 torr
(b) 140 torr
(c) 68 torr
(d) 20 torr

Answer : A

Question. During osmosis, flow of water through a semipermeable membrane is
(a) from solution having lower concentration only
(b) from solution having higher concentration only
(c) from both sides of semipermeable membrane with equal flow rates
(d) from both sides of semipermeable membrane with unequal flow rates. 

Answer : A

Question. 1.00 g of a non-electrolyte solute (molar mass 250 g mol^–1) was dissolved in 51.2 g of benzene. If the freezing point constant, Kf of benzene is 5.12 K kg mol^–1, the freezing point of benzene will be lowered by
(a) 0.2 K
(b) 0.4 K
(c) 0.3 K
(d) 0.5 K 

Answer : B

Question. A solution containing 10 g per dm3 of urea (molecular mass = 60 g mol^–1) is isotonic with a 5% solution of a non-volatile solute. The molecular mass of this non-volatile solute is
(a) 200 g mol^–1
(b) 250 g mol^–1
(c) 300 g mol^–1
(d) 350 g mol^–1

Answer : C

Question. The mixture which shows positive deviation from Raoult’s law is
(a) ethanol + acetone
(b) benzene + toluene
(c) acetone + chloroform
(d) chloroethane + bromoethane.

Answer : A

Question. For an ideal solution, the correct option is
(a) DmixG = 0 at constant T and P
(b) DmixS = 0 at constant T and P
(c) Dmix V ≠ 0 at constant T and P
(d) Dmix H = 0 at constant T and P. 

Answer : D

Question. The mixture that forms maximum boiling azeotrope is
(a) heptane + octane
(b) water + nitric acid
(c) ethanol + water
(d) acetone + carbon disulphide. 

Answer : B

Question. Which of the following statements is correct regarding a solution of two components A and B exhibiting positive deviation from ideal behaviour?
(a) Intermolecular attractive forces between A-A and B-B are stronger than those between A-B.
(b) Δmix H = 0 at constant T and P.
(c) Δmix V = 0 at constant T and P.
(d) Intermolecular attractive forces between A-A and B-B are equal to those between A-B.

Answer : A

Question. Which one of the following is incorrect for ideal solution?
(a) DHmix = 0
(b) DUmix = 0
(c) DP = Pobs – Pcalculated by Raoult’s law = 0
(d) DGmix = 0

Answer : D

Question. Which of the following statements about the composition of the vapour over an ideal 1 : 1 molar mixture of benzene and toluene is correct?
Assume that the temperature is constant at 25°C.
(Given, vapour pressure data at 25°C, benzene = 12.8 kPa, toluene = 3.85 kPa)
(a) The vapour will contain equal amounts of benzene and toluene.
(b) Not enough information is given to make a prediction.
(c) The vapour will contain a higher percentage of benzene.
(d) The vapour will contain a higher percentage of toluene. 

Answer : C

Question. Which condition is not satisfied by an ideal solution?
(a) DmixV = 0
(b) DmixS = 0
(c) Obeyance to Raoult’s Law
(d) DmixH = 0 

Answer : B

Question. 12g of urea is dissolved in 1 litre of water and 68.4 g of sucrose is dissolved in 1 litre of water.
The lowering of vapour pressure of first case is
(a) equal to second
(b) greater than second
(c) less than second
(d) double that of second

Answer : A

Question. At a particular temperature, the vapour pressures of two liquids A and B are respectively 120 and 180 mm of mercury. If 2 moles of A and 3 moles of B are mixed to form an ideal solution, the vapour pressure of the solution at the same temperature will be (in mm of mercury)
(a) 156
(b) 145
(c) 150
(d) 108

Answer : A

Question. A solution of urea (mol. mass 56 g mol^-1) boils at 100.18⁰C at the atmospheric pressure. If Kf and Kb for water are 1.86 and 0.512 K kg mol^-1 respectively, the above solution will freeze at
(a) 0.654⁰C
(b) -0.654⁰C 
(c) 6.54⁰C
(d) -6.54⁰C

Answer : B

ONE MARKQUESTIONS

1. Why do gases always tend to be less soluble in liquids as the temperature is raised?

2. ‘The osmotic pressure measured when benzoic acid is dissolved in benzene is less than the expected value’. Comment.

3. Which is the best colligative property to measure the molar masses of macro molecules? Why?

TWO MARK QUESTIONS

1. Define the term osmotic pressure. Describe how the molecular mass of a substance can be determined by a method based on measurement of osmotic pressure. (2008)

2.18 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? (Kb for water = 0.52 k kg mol^-1, boiling point of pure water = 373.15 K) (2013)

3.Define an ideal solution and write one of its characteristics. (2014)

4.Compare solubility of oxygen gas at 293K (K_H =35kbar) & at 393K (K_H =47kbar)

5.What are azeotropic mixtures? What are its types?

6. a) Why are aquatic species more comfortable in cold water than in warm water? b) What happens when we place the blood cell in saline water solution (hypertonic solution)? Give reason. 

THREE MARK QUESTIONS

1. Calculate the amount of KCl which must be added to 1 kg of water so that the freezing point is depressed by 2K. (Kf for water = 1.86 kg mol^-1)

2. Determine the osmotic pressure of a solution prepared by dissolving 2.5 x 10^-2 g of K₂SO₄ in 2L of water at 25⁰C, assuming that it is completely dissociated. (R = 0.0821 L atm K-1mol-1 , molar mass of K₂SO₄ = 174 g mol^-1)

3. A solution of glucose in water is labelled as 10% w/w, what would be the molality and mole fraction of each component in the solution? If the density of solution is 1.2 g mL^–1, then what shall be the molarity of the solution?

4. A solution containing 30 g of non-volatile solute exactly in 90 g of water has a vapour pressure of 2.8 kPa at 298 K. Further, 18 g of water is then added to the solution and the new vapour pressure becomes 2.9 kPa at 298 K. Calculate: (i) Molar mass of the solute (ii) Vapour pressure of water at 298 K.

5. Calculate the depression in the freezing point of water when 10 g of CH₃CH₂CHClCOOH is added to 250 g of water. Ka = 1.4 × 10^–3, Kf = 1.86 K kg mol^–1.

6. Two elements A and B form compounds having formula AB₂ and AB₄. When dissolved in 20 g of benzene (C₆H₆), 1 g of AB₂ lowers the freezing point by 2.3 K whereas 1.0 g of AB4 lowers it by 1.3 K. The molar depression constant for benzene is 5.1 K kg mol^–1. Calculate atomic masses of A and B.

7. Vapour pressure of water at 20⁰C is 17.5 mm Hg. Calculate the vapour pressure of water at 20⁰C when 15 g of glucose (Molar mass = 180 g mol^-1) is dissolved in 150 g of water.

FIVE MARK QUESTIONS

1. a) Explain the following:
i. Henry’s law about dissolution of a gas in a liquid.
ii. Boiling point elevation constant for a solvent.
b) 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 100.42 ⁰C. What mass of glycerol was dissolved to make this solution? (Kb for water = 0.512 K kg mol^-1)

2. a) On mixing acetone with chloroform, a reduction occurs in total volume. What type of deviations from ideal behavior for solutions is shown in this case and why?
b) Phenol associates in benzene to certain extent to form a dimer. A solution containing 20 g of phenol in 1.0 kg of benzene has its freezing point lowered by 0.69 K. Calculate the fraction of phenol that has dimerised. Given Kf for benzene = 5.1 K m^-1

3. What is van’t Hoff factor? What types of values can it have if in forming the solution the solute molecules undergo (i) Dissociation? (ii) Association?
(b) How many mL of a 0.1 M HCl solution are required to react completely with 1 g of a mixture of Na₂CO₃ and NaHCO₃ containing equimolar amounts of both ? (Molar mass : Na₂CO₃ = 106 g, NaHCO₃ = 84 g)

Important Questions for NCERT Class 12 Chemistry Solutions 

Question. Which of the following compounds can be used as antifreeze in automobile radiators?
(a) Methyl alcohol
(b) Glycol
(c) Nitrophenol
(d) Ethyl alcohol

Answer : B

Question. Concentrated aqueous sulphuric acid is 98% H₂SO₄ by mass and has a density of 1.80 g mL^–1. Volume of acid required to make one litre of 0.1 M H₂SO₄ solution is
(a) 16.65 mL
(b) 22.20 mL
(c) 5.55 mL
(d) 11.10 mL

Answer : C

Question. Which of the following is dependent on temperature?
(a) Molarity
(b) Mole fraction
(c) Weight percentage
(d) Molality 

Answer : A

Question. The vapour pressure of a solvent decreased by 10 mm of mercury when a non-volatile solute was added to the solvent. The mole fraction of the solute in the solution is 0.2. What should be the mole fraction of the solvent if the decrease in the vapour pressure is Nto be 20 mm of mercury?
(a) 0.4
(b) 0.6
(c) 0.8
(d) 0.2

Answer : B

Question. The vapour pressure of CCl4 at 25°C is 143 mm Hg.
If 0.5 g of a non-volatile solute (mol. weight = 65) is dissolved in 100 g CCl4, the vapour pressure of the solution will be
(a) 199.34 mm Hg
(b) 143.99 mm Hg
(c) 141.43 mm Hg
(d) 94.39 mm Hg. 

Answer : C

Question. What is the mole fraction of the solute in a 1.00 m aqueous solution?
(a) 1.770
(b) 0.0354
(c) 0.0177
(d) 0.177 

Answer : C

Question. How many grams of concentrated nitric acid solution should be used to prepare 250 mL of 2.0 M HNO₃? The concentrated acid is 70% HNO₃.
(a) 70.0 g conc. HNO₃
(b) 54.0 g conc. HNO₃
(c) 45.0 g conc. HNO₃
(d) 90.0 g conc. HNO₃

Answer : C

Question. The mole fraction of the solute in one molal aqueous solution is
(a) 0.009
(b) 0.018
(c) 0.027
(d) 0.036

Answer : B

Question. 2.5 litre of 1 M NaOH solution is mixed with another 3 litre of 0.5 M NaOH solution. Then find out molarity of resultant solution.
(a) 0.80 M
(b) 1.0 M
(c) 0.73 M
(d) 0.50 M

Answer : C

Question. How many g of dibasic acid (mol. weight 200) should be present in 100 mL of the aqueous solution to give strength of 0.1 N?
(a) 10 g
(b) 2 g
(c) 1 g
(d) 20 g 

Answer : C

Question. A solution containing 1.8 g of a compound (empirical formula CH₂O) in 40 g of water is observed to freeze at –0.465° C. The molecular formula of the compound is
(Kf of water = 1.86 kg K mol^–1)
(a) C₂H₄O₂
(b) C₃H₆O₃
(c) C₄H₈O₄
(d) C₆H₁₂O₆

Answer : D

Question. Which observation(s) reflect(s) colligative properties? 
(i) A 0.5 m NaBr solution has a higher vapour pressure than a 0.5 m BaCl2 solution at the same temperature
(ii) Pure water freezes at the higher temperature than pure methanol
(iii) a 0.1 m NaOH solution freezes at a lower temperature than pure water
Choose the correct answer from the codes given below
(a) (i), (ii) and (iii)
(b) (i) and (ii)
(c) (ii) and (iii)
(d) (i) and (iii)

Answer : D

 Question. At 300K, the vapour pressure of an ideal solution containing 3 mole of A and 2 mole of B is 600 torr.

At the same temperature, if 1.5 mole of A and 0.5 mole of C (non-volatile) are added to this solution the vapour pressure of solution increases by 30 torr. What is the value of 0
pB ?
(a) 940
(b) 405 
(c) 90
(d) None of these

Answer : C

Question. Exactly 1 g of urea dissolved in 75 g of water gives a solution that boils at 100.114°C at 760 torr. The molecular weight of urea is 60.1.
The boiling point elevation constant for water is
(a) 1.02
(b) 0.51 
(c) 3.06
(d) 1.51

Answer :  B

Question. An aqueous solution of NaCl shows the depression of freezing point of water equal to 0.372 K. The boiling point of BaCl2 solution of same molality will be [Kf (H₂O)= 1.86 K kg mol–1; Kb(H₂O) = 0.52 K kg mol^–1] 
(a) 100.52ºC
(b) 100.104ºC
(c) 101.56ºC
(d) 100.156ºC

Answer : D

1. Give an example of liquid in solid solution.

2. Give an example of solid in gas solution 

3. Which method of expressing concentration is used to express:-
(a) concentration of pollutants in air or water 
(b) concentration of medicines in pharmacy. 

4. Out of M and m, which is a better method of expressing concentration and why? 

5. Out of 1M and 1m, which solution is more concentrated and why? 

6. Presence of glucose in water decreases the vapour pressure of glucose solution. Why? 

7. Draw a plot of vapour pressure Vs mole fraction for a solvent in solution containing nonvolatile solution.

8. Raoult’s Law is a special case of Henry’s Law, Justify. 

9. What type of equilibrium exists in a solution of solid solute in liquid solvent at saturation point?

10. What is the effect of increase in temperature on solubility of NaCl in water given Δ_sol H = +ve?

11. What is the sign of enthalpy change for dissolution of a gas in liquid? 1

12. What type of deviation from Raoult’s Law is expected in a binary solution containing:-
(a) H₂O and HCl (b) Acetone and CS₂
Explain on the basis of interactions 

13. On what factor does the value of Kb and Kf depend? How can the values of Kb and Kf be calculated using thermodynamic quantities? 

14. A 0.004 M solution of Na₂SO₄ is isotonic with 0.01 M solution of glucose at same temperature.
Calculate degree of dissociation of Na₂SO₄. 

15. A solution of urea in water boils at 100.18⁰c at atmospheric pressure. If Kf and Kb for water are 1.86 and 0.52 Kkgmol-1, what will be the freezing point of this solution? 

16. Solution A contains 6 g of urea in 100 ml solution at 27⁰C while solution B contains 6 g of acetic acid in 100 ml at the same temp. Are the two solutions equimolar as well as isotonic? Justify. 

17. What are the characteristics of an azeotropic mixture? What type of azeotropic mixture will be formed by:- (a) Alcohol and water (b) Acetone and aniline 

18. Give reasons for the following: - 

(a) Fishes do not grow well in warm water.

(b) Calcium chloride is used to clear snow in cold countries.

(c) RBC burst when placed in contact with 0.1% NaCl solution.

(d) Out of all colligative properties, osmotic pressure is used to determine MB of macromolecules.

(e) Climbers usually develop symptoms of “ANOXIA”

(f) People eating lot of salty food suffer from “EDEMA”

19. Complete the following: -

(a) Depression in freezing point for 1M urea, 1M glucose and 1M NaCl are in ratio _____________

(b) In a dilute solution i for K4 [ Fe (CN)₆] is _________________

(c) Vant Hoff factor for Ba (NO₃)₂ solution is 2.74, its degree of dissociation is _________________

(d) Value of i for 0.1 m of NaCl is _______________ than that for 0.001 m NaCl solution.

(e) KH for He > KH for Ar ∴ solubility of ________________ is higher

Important Questions for NCERT Class 12 Chemistry Solutions
 

Question. A solution of acetone in ethanol
(a) obeys Raoult’s law
(b) shows a negative deviation from Raoult’s law
(c) shows a positive deviation from Raoult’s law
(d) behaves like a near ideal solution.

Answer : C

Question. A solution containing components A and B follows Raoult’s law
(a) A - B attraction force is greater than A - A and B - B
(b) A - B attraction force is less than A - A and B - B
(c) A - B attraction force remains same as A - A and B - B
(d) volume of solution is different from sum of volume of solute and solvent. 

Answer : C

Question. All form ideal solution except
(a) C₆H₆ and C₆H₅CH₃
(b) C₂H₆ and C₂H₅I
(c) C₆H₅Cl and C₆H₅Br
(d) C₂H₅I and C₂H₅OH

Answer : D

Question. An ideal solution is formed when its components
(a) have no volume change on mixing
(b) have no enthalpy change on mixing
(c) have both the above characteristics
(d) have high solubility.

Answer : C

Question. The freezing point depression constant (Kf) of benzene is 5.12 K kg mol^–1. The freezing point depression for the solution of molality 0.078 m containing a non-electrolyte solute in benzene is (rounded off upto two decimal places)
(a) 0.20 K
(b) 0.80 K
(c) 0.40 K
(d) 0.60 K

Answer : C

Question. If molality of the dilute solution is doubled, the value of molal depression constant (Kf) will be
(a) halved
(b) tripled
(c) unchanged
(d) doubled. 

Answer : C

Question. At 100°C the vapour pressure of a solution of 6.5 g of a solute in 100 g water is 732 mm. If Kb = 0.52, the boiling point of this solution will be
(a) 102 °C
(b) 103 °C
(c) 101 °C
(d) 100 °C

Answer : C

Question. 200 mL of an aqueous solution of a protein contains its 1.26 g. The osmotic pressure of this solution at 300 K is found to be 2.57 × 10^–3 bar. The molar mass of protein will be (R = 0.083 L bar mol–1 K^–1)
(a) 51022 g mol^–1
(b) 122044 g mol^–1
(c) 31011 g mol^–1
(d) 61038 g mol^–1

Answer : D

Question. A solution containing 10g per dm3 of urea (molecular mass = 60 gmol^–1) is isotonic with a 5% solution of a non volatile solute. The molecular mass of this non volatile solute is 
(a) 300 g mol^–1
(b) 350 g mol^–1
(c) 200 g mol^–1
(b) 250 g mol^–1

Answer : A

Question. The vapour pressure of a solvent decreases by 10 mm of Hg when a non-volatile solute was added to the solvent. The mole fraction of the solute in the solution is 0.2. What should be the mole fraction of the solvent if the decrease in the vapour pressure is to be 20 mm of Hg ?
(a) 0.8
(b) 0.6
(c) 0.4
(d) 0.2

Answer : B

Question. Which of the following salts has the same value of van’t Hoff factor (i) as that of K₃[Fe(CN)₆]?
(a) Na₂SO₄
(b) Al(NO₃)₃
(c) Al₂(SO₄)₃
(d) NaCl

Answer : B

Question. At 25°C, the highest osmotic pressure is exhibited by 0.1 M solution of
(a) glucose
(b) urea
(c) CaCl₂
(d) KCl. 

Answer : C

Question. Which of the following aqueous solution has minimum freezing point?
(a) 0.01 m NaCl
(b) 0.005 m C₂H₅OH
(c) 0.005 m MgI₂
(d) 0.005 m MgSO₄ 

Answer : A

Question. pA and pB are the vapour pressures of pure liquid components, A and B, respectively of an ideal binary solution. If xA represents the mole fraction of component A, the total pressure of the solution will be
(a) pA + xA(pB – pA)
(b) pA + xA ( pA – pB)
(c) pB + xA(pB – pA)
(d) pB + xA ( pA – pB)

Answer : D

Question. Vapour pressure of chloroform (CHCl₃) and dichloromethane (CH₂Cl₂) at 25°C are 200 mm Hg and 41.5 mm Hg respectively. Vapour pressure of the solution obtained by mixing 25.5 g of CHCl₃ and 40 g of CH₂Cl₂ at the same temperature will be (Molecular mass of CHCl₃ = 119.5 u and molecular mass of CH₂Cl₂ = 85 u)
(a) 173.9 mm Hg
(b) 615.0 mm Hg
(c) 347.9 mm Hg
(d) 285.5 mm Hg

Answer : None