Sampling Distributions (1) If u ∼ χ 2 (m) and v ∼ χ 2 (n) are independent chi-square variates with m and n degrees of freedom respectively, then F = u m ˆ v. The National Centers for Environmental Information (NCEI) has launched a new divisional climate dataset called nClimDiv.This dataset replaces the traditional Drd964x values.
Important Questions for CBSE Class 12 Chemistry Solutions
Previous Years' Questions
2015
Short Answer Type Questions [I] [2 Marks]
1. (i)On mixing liquid X and liquid Y, the volume of the resulting solution increases. What type of deviation from Raoult's law is shown by the resulting solution? What change in temperature would you observe after mixing liquids X and Y?
(ii) How can the direction of osmosis be reversed? Write one use of reverse
osmosis.
Answer: (i) Positive deviation. The temperature will decrease.
(ii) When we apply pressure on solution side more than osmotic pressure, osmosis can be reversed. It is used for desalination of sea water.
2. What do you understand by depression of freezing point? Derive the relationship between depression of freezing point and molar mass of the solute.
Answer: The decrease in freezing point when non-volatile solute is added to a solvent, is called depression in freezing point.
3. State Henry's law. Why do gases always tend to be less soluble in liquids as
the temperature is raised?
Answer: Henry's law states, ‘The partial pressure of the gas dissolved in a liquid is directly proportional to its mole fraction. pgas= KH xgas, where xgas is the mole fraction of gas and pgas is the partial pressure of the gas.
When temperature is increased, KH (Henry's law constant) increases, therefore, the solubility of gases in liquid decreases.
4. State Raoult's law for the solution containing volatile components. Write two differences between an ideal solution and a non-ideal solution.
Answer: Raoult's law: It states that partial vapour pressure of each component is directly proportional to their mole fraction if both solute and solvent are volatile.
5. Why does a solution containing non-volatile solute have higher boiling point than the pure solvent? Why is elevation of boiling point a colligative property?
Answer: When we add a non-volatile solute to a pure solvent, the vapour pressure of solution decreases, therefore, it is to be heated to higher temperature so that its vapour pressure becomes equal to the atmospheric pressure, i.e. its boiling point will be higher.
Elevation of boiling point is a colligative property because it depends upon the number of particles of solute and not on nature of solute.
6. Derive the relationship between relative lowering of vapour pressure and molar mass of the solute.
Answer:
7. What is meant by positive deviations from Raoult's law? Give an example. What is the sign of ΔmixH for positive deviation?
Answer: Those solutions in which force of attraction between A—B is less than A—A and B—B, shows positive deviation from Raoult's law, e.g. ethanol and water show positive deviation from Raoult's law.
ΔmixH=+ve
8. Define azeotropes. What type of azeotrope is formed by positive deviation from Raoult's law? Give an example.
Answer: Azeotropes are the constant boiling mixtures which distill out unchanged in their composition.
Minimum boiling azeotropes are formed by the solutions showing positive deviation, e.g. cyclohexane and ethanol.
9. (i) On mixing liquid X and liquid Y, volume of the resulting solution decreases. What type of deviation from Raoult's law is shown by the resulting solution? What change in temperature would you observe after mixing liquids X and Y? .
(ii) What happens when we place the blood cell in water (hypotonic solution)? Give reason.
Answer: (i) The resulting solution will show negative deviation from Raoult's law. The temperature of solution will increase.
(ii) The cell will swell and even may burst due to inflow of solvent because osmosis.
10. What is meant by negative deviation from Raoult's law? Give an example. What is the sign of AmixH for negative deviation?
Answer: A solution is said to deviate negatively from Raoult's law if the forces of attraction between A—B are more than A—A and B—B, e.g. CHCl3and CH3COCH3.
ΔmixH=-ve
Short Answer Type Questions [II] [3 Marks]
11. Define azeotropes. What type of azeotrope is formed by negative deviation from Raoult's law. Give an example.
Answer: Azeotropes are the constant boiling mixtures which distill out unchanged in their composition.
Maximum boiling azeotropes are formed by the solution showing negative deviation, e.g. H2O and HCl.
12. Vapour pressure of water at 20 °C is 17.5 mm Hg. Calculate the vapour pressure of water at 20 °C when 15 g of glucose (Molar mass = 180 g mol-1) is dissolved in 150 g of water.
Answer:
13. A solution is prepared by dissolving 5 g of non-volatile solute in 95 g of water. It has a vapour pressure of 23.375 mm Hg at 25°C. Calculate the piolar mass of the solute, (vapour pressure of pure water at 25 °C is 23.75 mm Hg).
Answer:
14. When 1.5 g of a non-volatile solute was dissolved in 90 g of benzene, the boiling point of benzene raised from 353.23 K to 353.93 K. Calculate the molar mass of the solute. (Kb for benzene = 2.52 kg mol-1)
Answer:
15. Calculate the freezing point of the solution when 31 g of ethylene glycol (C2H6O2) is dissolved in 500 g of water. (Ky for water = 1.86 K kg mol-1)
Answer:
16. 3.9 g of benzoic acid dissolved in 49 g of benzene shows a depression in freezing point of 1.62 K. Calculate the van't Hoff factor and predict the nature of solute (associated or dissociated).;(Given: Molar mass of benzoic acid = 122 g mol-1, Ky for benzene = 4.9 K kg mol-1)
Answer:
17. A solution is prepared by dissolving 10 g of non-volatile solute in 200 g of water. It has a vapour pressure of 31.84 mm Hg at 308 K. Calculate the molar mass of the solute. (Vapour pressure of pure water at 308 K = 32 mm Hg)
Answer:
18. Calculate the mass of NaCl (molar mass = 58.5 g mol-1) to be dissolved in 37.2 g of water to lower the freezing point by 2 °C, assuming that NaCl undergoes complete dissociation. (Ky for water = 1.86 K kg mol-1)
Answer:
2014
Very Short Answer Type Questions [1 Mark]
19. What possible value of ‘i' will it have if solute molecules undergo association
in solution?
Answer: i < 1, if solute molecules undergo association.
20. Some liquids on mixing form ‘azeotropes'. What are ‘azeotropes'?
Answer: Azeotropes are the constant boiling mixtures which distill out unchanged in their composition.
21. What type of intermolecular attractive interaction exists in the pair of methanol
and acetone?
Answer: H-bonding exists between methanol and acetone. It also has dipole-dipole attraction.
22. What are isotonic solutions?
Answer: Those solutions which exert same osmotic pressure because they have same molar concentrations and same number of particles are called isotonic solutions.
https://soft-homes.mystrikingly.com/blog/thunderbolt-portable-hard-drive-2tb. Short Answer Type Questions [I] [2 Marks]
23. How is vapour pressure of solvent affected when a non-volatile solute is dissolved in it?
Answer: Vapour pressure of solution decreases because surface consists of bpth solute and solvent molecules. The escaping tendency of solvent into vapours decreases.
24. Differentiate between molarity and molality of solution. How can we change molality value into molarity value.
Answer: Molarity is the number of moles of solute dissolved per litre of solution, whereas molality is the number of moles of solute dissolved per kg of solvent.
25. Calculate the mass of compound (molar mass = 256 g mol-1) to be dissolved in 75 g of benzene to lower its freezing point by 0.48 K (Kj = 5.12 K kg mol-1).
Answer:
26. Define an ideal solution and write one of its characteristics.
Answer: Ideal solution is a solution which follows Raoult's law.
Characteristics:
27. State Henry's law. What is the effect of temperature on the solubility of a gas in a liquid?
Answer: Henry's Law: The mole fraction of a gas in a solution (solubility of gas in liquid) is directly proportional to partial pressure of gas over solution.
where KH is Henry's law constant, %gas is mole fraction of gas and ^gas is the partial pressure of gas.
The solubility of a gas decreases with increase in temperature. Dropsync 3 1 1 download free.
28. State Raoult's law for the solution containing volatile components. What is the similarity between Raoult's law and Henry's law?
Answer:
Short Answer Type Questions [II] [3 Marks]
29. Some ethylene glycol, HOCH2CH2OH, is added to your car's cooling system along with 5 kg of water. If the freezing point of water glycol solution is -15°C, what is the boiling point of the solution. [Kft = 0.52 K kg mol-1 and Ky = 1.86 K kg mol-1 for H2O.
Answer:
Long Answer Type Questions [5 Marks]
30. (a) Define the following terms:
(i) Molarity (ii) Molal elevation constant (Kb) ‘
(b) A solution containing 15 g urea (molar mass = 60 g mol-1) per litre of solution in water has the same osmotic pressure (isotonic) as a solution of glucose (molar mass = 180 g mol-1) in water. Calculate the mass of glucose present in one litre of its solution.
Answer:
31. (a) What type of deviation is shown by a mixture of ethanol and acetone? Give reason.
(b) A solution of glucose (molar mass = 180 g mol-1) in water is labelled as 10% (by mass). What would be the molality and molarity of the solution? (Density of solution = 1.2 g mL1 )
Answer:
32. (a) State Raoult's law for a solution containing volatile components. Name the solution which follows Raoult's law at all concentrations and temperatures.
(b) Calculate the boiling point elevation for a solution prepared by adding 10 g of CaCl2 to 200 g of water. (Kb for water = 0.512 K kg mol-1, Molar mass of CaCl2 = 111 g mol-1)
Answer:
33.(a) Define the following terms:
(i) Azeotrope (ii) Osmotic pressure (iii) Colligative properties
(b) Calculate the molarity of 9.8% (w/w) solution of H2S04 if the density of the solution is 1.02 g mL-1 (Molar mass of H2S04 = 98 g mol-1).
Answer:
2013
Very Short Answer Type Questions [1 Mark]
34. Define osmotic pressure.
Answer: Refer Ans. to Q.33 (ii).
35. Measurement of which colligative property is preferred for determination of molar mass of biomolecules?
Answer: Osmotic pressure is preferred for determining molecular weight of biomolecules.
Observe 1 86 12 Nkjv
Short Answer Type Questions [I] [2 Marks]
36. What type of deviation is shown by a mixture of ethanol and acetone? What type of azeotrope is formed by mixing ethanol and acetone?
Answer: Positive deviation is shown by a mixture of ethanol and acetone. Minimum boiling azeotropes are formed.
37. Out of two 0.1 molal solutions of glucose and of potassium chloride, which one will have a higher boiling point and why?
Answer: 0.1 molal KC1 solution will have higher boiling point, because KC1 dissociates into K+ and Cl–ions. The number of particles are double than 0.1 m glucose solution, therefore, higher ATa, hence higher the boiling point.
38. 18 g of glucose, C6H1206 (Molar Mass = 180 g mol-1) is dissolved in 1 kg of water in a sauce pan. At what temperature will this solution boil? (Kh for water = 0.52 K kg mol-1, boiling point of pure water = 373.15 K)
Answer:
39. Henry's law constant (KH) for the solution of methane in benzene at 298 K is 4.27 X 105 mmHg. Calculate the solubility of methane in benzene at 298 K under 760 mm Hg.
Answer:
40. (i) Why is an increase in temperature observed on mixing chloroform and acetone?
(ii) Why does sodium chloride solution freeze at a lower temperature than water?
Answer: (i) It is because force of attraction between chloroform and acetone is more than the force of attraction between CHC13—CHC13 or Acetone-Acetone. Therefore, AH = -ve, i.e. exothermic process, therefore, there is increase in temperature.
(ii) It is because when NaCl is added, vapour pressure of solution becomes less and at a lower temperature, vapour pressure of solid and solution will become equal, i.e. freezing point is lowered.
Short Answer Type Questions [II] [3 Marks] https://quivagabun1981.wixsite.com/connectdownload/post/what-are-the-versions-of-osx.
41. Determine the osmotic pressure of a solution prepared by dissolving 2.5 X 10-2 g of K2S04 in 2 L of water at 25 °C, assuming that it is completely dissociated. (R = 0.0821 L atm K-1 mol-1, Molar mass of K2so4= 174 g mol-1).
Answer:
Long Answer Type Questions [5 Marks]
42. (a) State Raoult's law for a solution containing volatile components. How does Raoult's law become a special case of Henry's law?
(b) 1.00 g of a non-electrolyte solute dissolved in 50 g of benzene lowered the freezing point of benzene by 0.40 K. Find the molar mass of the solute. (Kyfor benzene = 5.12 K kg mol-1)
Answer:
43. (a) Define the following terms: .
(i) Ideal solution (ii) Azeotrope (iii) Osmotic pressure
(b) A solution of glucose (C6H1206) in water is labelled as 10% by weight. What would be the molality of the solution?
(Molar mass of glucose = 180 g mol-1)
Answer:
Very Short Answer Type Questions [1 Mark]
44. Define Ebullioscopic constant.
Answer: Ebullioscopic Constant (Boiling Point Elevation Constant): It is equal to the elevation in boiling point of 1 molal solution, i.e. 1 mole of solute is dissolved in 1 kg of solvent. The unit of is K molal-1 or KJm or K kg mol-1
45. State Raoult's law for a solution containing volatile components.
Answer: The vapour pressure of each component is direcdy proportional to mole fraction of each component.
46. Define ‘mole fraction' of a substance in a solution.
Answer: Mole fraction of a substance is defined as the ratio of number of moles of substance to the total number of moles of solute and solvent, i.e. all the substances.
47. Why are aquatic species more comfortable in cold water in comparison to warm water?
Answer: Cold water has more dissolved oxygen than warm water because solubility of gas in liquid decreases with increase in temperature.
Short Answer Type Questions [I] [2 Marks]
48. A 1.00 molal aqueous solution of trichloroacetic acid (CCl3COOH) is heated to its boiling point. The solution has the boiling point of 100.18 °C. Determine the van't Hoff factor for trichloroacetic acid. (Kft for water = 0.512 K kg mol-1)
Answer:
49. Define the following terms:
(i)Mole fraction (ii)Isotonic solutions (iii)van't Hoff factor (iv)Ideal solution
Answer:
50. The density of water of a lake is 1.25 g mL-1 and one kg of this water contains 92 g of Na+ ions. What is the molarity of Na+ ions in the water of the lake? (Atomic mass of Na = 23.00 u)
Answer:
Short Answer Type Questions [II] [3 Marks]
51. Calculate the amount of KC1 which must be added to 1 kg of water so that the freezing point is depressed by 2 K. (Ky for water = 1.86 kg mol-1)
Answer:
52. At 25 °C the saturated vapour pressure of water is 3.165 kPa (23.75 mm Hg). Find the saturated vapour pressure of a 5% aqueous solution of urea (carbamide) at the same temperature. (Molar mass of urea = 60.05 g mol-1)
Answer:
53. Calculate the freezing point depression expected for 0.0711m aqueous solution of Na2S04. If this solution actually freezes at – 0.320 °C, what would be the value of van't Hoff factor? (Ky for water is 1.86 °C mol-1).
Answer:
Long Answer Type Questions [5 Marks]
54. (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 (C3Hg03) in water was prepared by dissolving some glycerol in 500 g of water. This solution has a boiling point of 100.42 °C. What mass of glycerol was dissolved to make this solution? (Kf for water = 0.512 K kg mol-1)
Answer: (a) (i) Henry's Law: It states that the solubility of a gas in a liquid is directly proportional to the pressure of the gas.
p = KHx, where p is pressure of gas, x is the mole fraction of the gas and KH is Henry's law constant.
{ii) Boiling Point Elevation Constant (Molal Boiling Point Elevation Constant). It is equal to the elevation in boiling point of 1 molal solution, i.e. 1 mole of solute is dissolved in 1 kg of solvent. It is also called ebullioscopic constant. The unit of is K/m or K kg mol-1.
2011
Very Short Answer Type Questions [1 Mark]
55. State Raoult's law in its general form with respect to solutions.
Answer: The partial vapour pressure of each component in solution is directly proportional to its mole fraction if both components are volatile.
56. Define Henry's law about solubility of a gas in a liquid.
Answer: Henry's law states that partial pressure of the gas is directly proportional to its mole fraction.
57. What is meant by ‘reverse osmosis'?
Answer: Reverse Osmosis: If extra pressure is applied on the solution side and exceeds the osmotic pressure, the osmosis can be reversed. That is, pure water can be forced out of the solution to pass through the pores of the membrane in the opposite direction. This is called reverse osmosis.
58. State Raoult's law for a solution containing volatile components.
Answer: Refer Ans. to Q. 45.
Short Answer Type Questions [I] [2 Marks]
59. A 0.561 m solution of an unknown electrolyte depresses the freezing point of water by 2.93 °C. What is van't Hoff factor for this electrolyte? The freezing point depression constant (Kf) for water is 1-86 °C kg mol-1
Answer:
Short Answer Type Questions [II] [3 Marks]
60.What would be the molar mass of a compound if 6.21 g of it dissolved in 24.0 g of chloroform forms a solution that has a boiling point of 68.04 °C? The boiling point of pure chloroform is 61.7 °C and the boiling point elevation constant, for chloroform is 3.63 °C/m.
Answer:
Observe 1 86 12 Kjv
61. What mass of NaCl (molar mass = 58.5 g mol-1) must be dissolved in 65 g of water to lower the freezing point by 7.50 °C? The freezing point depression constant, Kffor water is 1.86 K kg mol-1. Assume van't Hoff factor for NaCl is 1.87.
Answer:
62. (a) Differentiate between molarity and molality for a solution. How does a change in temperature influence their values?
(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 g mol-1) (Kf for water is 1.86 K kg mol-1)
Answer:
63. (a) Define the terms osmosis and osmotic pressure. Is osmotic pressure of a solution a colligative property? Explain.
(b) Calculate the boiling point of a solution prepared by adding 15.00 g of NaCl to 250.0 g of water.
(Kf for water = 0.512 K kg mol-1, Molar mass of NaCl = 58.44 g)
Answer: (a) Osmosis: When a solvent is separated from the solution by a semi-permeable membrane which allows the passage of solvent molecules but does not allow solute particles to pass through it, there is net flow of solvent molecules from the.solvent to the solution which is called osmosis.
Osmotic Pressure: Osmotic pressure may be defined as extra pressure that must be applied to the solution side to prevent osmosis (the flow of solvent into solution through a semi-permeable membrane.)
64. (a) State the following:
(i) Henry's law about partial pressure of a gas in a mixture.
(ii) Raoult's law in its general form in reference to solutions.
(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 torr at 25 °C. Assuming the gene fragment is non-electrolyte, determine its molar mass.
Answer: (i) Henry's Law. It states that the partial vapour pressure of a gas in vapour phase is directly proportional to the mole fraction of the gas in the solution.
where KH is Henry's law constant, x is mole fraction of gas in solution and p is partial vapour pressure of the gas in solution.
(ii) Raoult's Law for solution of Non-volatile Solute. The relative lowering of vapour pressure for a solution is equal to the mole fraction of solute when solvent alone is volatile.
65. (a) The molecular masses of polymers are determined by osmotic pressure method and not by measuring other colligative properties. Give two reasons.
(b) At 300 K, 36 g of glucose, C6H1206 present per litre in its solution has an
osmotic pressure of 4.98 bar. If the osmotic pressure of another glucose solution is 1.52 bar at the same temperature, calculate the concentration of the other solution.
Answer: (a) (i) It is measured at room temperature.
(ii) It has appreciable value.
66. (a) List any four factors on which the colligative properties of a solution depend.
(b) Calculate the boiling point of one molar aqueous solution (density 1.06 gmL-1) of KBr. [Given: Kb for H2O = 0.52 K kg mol-1, Atomic mass: K = 39, Br = 80]
Answer:
67. (a) Explain why a solution of chloroform and acetone shows negative deviation from Raoult's law.
(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 Km-1]
Answer: (a) It is due to formation of H-bonding due to which escaping tendency of molecules and vapour pressure of the solution decrease, therefore, boiling point of the solution increases. Hence, such solution shows negative deviation from Raoult's law.
(b) ATy = 0.69 K, Ky = 5.1 K/m,
WB = 20 g, WA = 1 kg = 1000 g
Observe 1 86 120
68. (a) What is van't Hoff factor? What possible values can it have if the solute molecules undergo dissociation?
(b) An aqueous solution containing 12.48 g of barium chloride in 1.0 kg of water boils at 373.0832 K. Calculate the degree of dissociation of barium chloride. [Given for H20 = 0.52 K m-1; Molar mass of BaCl2= 208.34 g mol-1]
Answer:
2010
Very Short Answer Type Questions [1 Mark]
69. How is the molality of a solution different from its molarity?
Answer: Molality is defined as the number of moles ofsolute dissolved per kg ofsolvent, whereas
molarity is defined as the number of moles of solute dissolved in per litre of solution.
70. State Raoult's law for a solution containing volatile components.
Answer: Refer Ans. to Q. 45.
Short Answer Type Questions [I] [2 Marks]
71. Non-ideal solutions exhibit either positive or negative deviations from Raoult's
law. What are these deviations and how are they caused?
Answer: Positive Deviation from Raoult's Law: In those non-ideal solutions, in which partial pressure of each component A and B is higher than that calculated from Raoult's 1? show positive deviation from Raoult's law, e.g. water and ethanol. Negative Deviation from Raoult's Lawr: The partial vapour pressure of component A is found to be less than calculated from Raoult's law' on adding the second component B and when A is added to B, the partial vapour pressure of component B is found to be less than that calculated from Raoult's law.
72. State Henry's law and mention its two important applications.
Answer: Henry's Law: It states that the partial vapour pressure of gas in vapour phase is directly proportional to the mole fraction of the gas in the solution.
Applications of Henry's Law:
(i) To minimise the painful effects of deep sea divers, oxygen diluted with less soluble helium gas is used as breathing gas instead of air because nitrogen is more soluble in blood and cause pain or bends.
(ii) To increase the solubility of COs in soft drinks and soda water, the bottle is sealed under high pressure.
73. Find the boiling point of a solution containing 0.520 g of glucose (C6H1206) dissolved in 80.2 g of water. [Given: Kf for water = 0.52 K/m]
Answer:
Short Answer Type Questions [II] [3 Mark]
Observe 1 86 123
74. Define the term, ‘molarity of a solution'. State one disadvantage in using the molarity as the unit of concentration.
Answer: Molarity is defined as the number of moles of solute dissolved per litre of solution. Its disadvantage is that it changes with change in temperature and volume of solute is not taken into account.
75. What mass of ethylene glycol (molar mass = 62.0 g mol-1) must be added to 5.50 kg of water to lower the freezing point of water from 0 °C to -10.0 °C? (Kf for water = 1.86 K kg mol-1)
Answer:
76. 15 g of an unknown molecular substance was dissolved in 450 g of water. The resulting solution freezes at – 0.34 °C. What is the molar mass of the substance? (Kf for water = 1.86 K kg mol-1)
Answer:
Long Answer Type Questions [5 Marks]
77. (a) Define the terms osmosis and osmotic pressure. What is the advantage of using osmotic pressure as compared to other colligative properties for the determination of molar masses of solutes in solutions?
(b) A solution prepared from 1.25 g of oil of wintergreen (methyl salicylate) in 90.0 g of benzene has a boiling point of 80.31 °C. Determine the molar mass of this compound. (Boiling point of pure benzene = 80.10 °C and K& for benzene = 2.53 °C kg mol-1)
Answer: (a) Osmosis: When a solution is separated from the solvent by a semi-permeable membrane which allows the passage of solvent molecules but does not allow solute particles to pass through it, there is net flow of solvent molecules from the solvent to the solution which is called osmosis.
Do i need get office. Osmotic Pressure: Osmotic pressure may be defined as extra pressure that must be applied to the solution side to prevent the flow of solvent into solution through a semi-permeable membrane. Osmotic pressure is determined at room temperature and has appreciable value which can be easily measured.
2009
Very Short Answer Type Questions [1 Mark]
78. State ‘Raoult's Law' for a solution of volatile liquids.
Answer: Refer Ans. to Q.45.
79. Define an ideal solution.
Answer: Refer Ans. to Q.43 (a) (i).
80. Measurement of which colligative property is preferred for determination of molar mass of biomolecules?
Answer: Refer Ans. to Q.35.
81. What is meant by‘reverse osmosis'?
Answer: Refer Ans. to Q.57.
Short Answer Type Questions [II] [3 Marks]
82. 100 mg of a protein is dissolved in just enough water to make 10.0 mL of solution. If this solution has an osmotic pressure of 13.3 mm Hg at 25 °C, what is the molar mass of the protein? (R = 0.0821 L atm mol-1K-1and 760 mm Hg = 1 atm)
Answer:
83. Calculate the freezing point depression expected for 0.0711 m aqueous solution of Na2S04. If this solution actually freezes at – 0.320 °C, what would be the value of van't Hoff factor? (Ky for water is 1.86 °C mol-1).
Answer: Refer Ans. to Q.53.
84. Calculate the amount of sodium chloride which must be added to one kilogram of water so that the freezing point of water is depressed by 3 K. [Given: Kf = 1.86 K kg mol-1, Atomic mass: Na = 23.0, Cl = 35.5]
Answer:
85. A solution of urea in water has a boiling point of 373.128 K. Calculate the freezing point of the same solution. [Given: For water, Kf = 1.86 Km-1,Kb = 0.52 Km-1]
Answer:
86. 0.1 mole of acetic acid was dissolved in 1 kg of benzene. Depression in freezing point of benzene was determined to be 0.256 K. What conclusion can you draw about the state of the solute in solution?
Answer:
Long Answer Type Questions [5 Marks]
87. (a) What is meant by:
(i) Colligative properties (ii) Molality of a solution
(b) What concentration of nitrogen should be present in a glass of water at room temperature? Assume a temperature of 25 °C, a total pressure of 1 atmosphere and mole fraction of nitrogen in air of 0.78. [KHfor nitrogen = 8.42 X 10-7M/mm Hg]
Answer: (a) (i) Colligative properties: Those properties of solutions which depend upon the number of particles of solute and solvent but not on the nature of solute are called colligative properties.
(ii) Molality of a solution: It is defined as the number of moles of solute dissolved in per 1000 g or 1 kg of solvent.
