Short & Long Answer Questions: Solutions - 2 - Grade 12 PDF Download

Q.51. Define osmosis and osmotic pressure.
Ans. Osmosis: The process of flow of solvent from a dilute solution to a concentrated solution through a semipermeable membrane is called osmosis.
Osmotic pressure: The driving force responsible for the process of osmosis is called osmotic pressure.

Q.52. What is meant by abnormal molecular mass of solute? Which factor is responsible for abnormality in molecular masses of solutes using colligative properties?
Ans. When the observed value of molecular mass is different from the normal value, it is called abnormal molecular mass. Abnormality in molecular mass arises when solute undergoes association or dissociation in the solution.

Q.53. The molecular mass of ethanoic acid when determined by colligative property of its solution is abnormal. Explain why?
Ans. Ethanoic acid undergoes association in non-polar solvent and dissociation in polar solvent. Hence, its molecular mass is abnormal.

Q.54. 
(a) What is solubility of a substance? 
(b) On what factors solubility of solid depends? 
(c) What is the effect of pressure on solubility?
Ans. Refer text 2.1.2 and 2.1.3.

Q.55. 
(a) Define vapour pressure. 
(b) State and explain Raoult's law for a solution of volatile liquids. 
(c) State Raoult's law for a solution of non-volatile solute.
Ans. 
(a) Refer text 2.3.
(b) Refer text 2.3.1.
(c) Refer text 2.3.4.

Q.56. What are ideal and non-ideal solutions? Explain each with diagram and suitable examples.
Ans. Refer text 2.3.2.

Q.57. Explain the terms: 
(a) Elevation in boiling point. 
(b) Depression in freezing point. 
(c) Relative lowering of vapour pressure. 
(d) Osmotic pressure. 
Ans. 
(a) Refer text 2.4.2.
(b) Refer text 2.4.3.
(c) Refer text 2.4.1.
(d) Refer test 2.4.4.

Q.58. What is van't -Hoff factor? How is it used to calculate molecular mass of a non-volatile substances?
Ans. Refer test 2.6.

Q.59. What happens when RBC are placed in 
(i) 1% NaCI solution. 
(ii) Pure water.
Ans. 
(i) RBC is hypotonic with 1% NaCI hence it will shrink due to plasmolysis.
(ii) RBC is hypertonic with pure water hence it will swell or even burst due to hemolysis.

Q.60. 4% NaOH solution (mass/volume) and 6% urea solution (mass/volume) are equimolar but not isotonic. Why?
Ans. Both the solutions 4% NaOH (WIV) and 6% urea (WIV) have same concentration (1 M) but these are not isotonic because NaOH undergoes dissociation in solution. Therefore, number of particles in NaOH solution is more than that in urea solution.

Q.61. Name the solid that is separated when salt solution is slowly frozen.
Ans. Ice separates out first because freezing point of salt solution is less than pure water.

Q.62. Why do aquatic species feel more comfortable in winter than in summer?
Ans. In winter season at low temperature solubility of oxygen in water is higher than that in summer at high temperature. Hence, species feel more comfortable in winter than in summer.

Q.63. What precaution should be taken in intravenous injection?
Ans. The medicine to be given by intravenous injection should be isotonic with blood plasma. If hypertonic solution is injected intravenously then RBC will shrink (crenation). If hypotonic solution is injected intravenously then RBC will swell or even burst (hemolytic).

Q.64. A mixture of ethyl alcohol and water cannot be separated into pure component by fractional distillation. Why? 
Ans. Ethyl alcohol and water form an azeotropic mixture which distills over as a pure liquid and cannot be separated by fractional distillation.

Q.65. Give one example of interstitial and substitutional solid solutions.
Ans. Tungsten carbide is an example of interstitial solid solution while brass (alloy of Cu and Zn) represents substitutional solid solution.

Q.66. How is Henry's Law constant related to the solubility of a gas in a solvent?
Ans. KH is inversely proportional to the solubility of a gas in a solvent.

Q.67. How can you compare the relative solubilities of different salts in the same solvent?
Ans. The relative solubilities can be compared in terms of solubility product constant (K_sp) values i.e., more the K_sp value, more will be the solubility of the salt.

Q.68. What does normality (N) represent? 
Ans. It represents the number of gram equivalents of the solute dissolved per litre of the solution. Its unit is equivalent. L^-1.

Q.69. Why does not molality of the solution change with temperature?
Ans. It takes into account only the mass of the solute as well of the solvent. Both of them do not change with change in temperature.

Q.70. What are the units of mole fraction?
Ans. Mole fraction being a ratio has no units.

Q.71. What should be the nature of the solution while representing the solubility of a solute?
Ans. Solution must be saturated in nature.

Q.72. Rubbing isopropyl alcohol often gives a cooling sensation to the skin. Why?
Ans. Isopropyl alcohol (CH₃CHOHCH₃) being a volatile liquid absorbs the required latent heat of vaporization from the skin thereby giving a cooling sensation.

Q.73. What will happen to the boiling point of the solution on mixing two miscible liquids showing negative deviation from Raoult's law?
Ans. The vapour pressure of the solution will decrease and its boiling point will increase.

Q.74. The bottle of liquid ammonia is generally cooled before opening the seal. Assign reason.
Ans. On cooling, the gas will tend to liquefy and its vapour pressure will decrease. Therefore, the gas will not come with force upon opening the seal.

Q.75. Does osmosis occur from hypertonic solution to hypotonic solution?
Ans. No, it always occurs from hypotonic to hypertonic solution.

Q.76. What type of azeotrope will result on mixing chloroform and acetone?
Ans. It will result in maximum boiling azeotrope because liquid mixture shows negative deviation from Raoult's Law.  

Q.77. Name the most commonly used semi permeable membrane in the laboratory.
Ans. It is copper ferrocyanide Cu₂[Fe(CN)₆] and is formed by mixing equimolar aqueous CuSO₄ and K₄[Fe(CN)₆] solutions

Q.78. The Van't Hoff factor of a solution is 1. What does it indicate?
Ans. It indicates that the solute does not undergo either dissociation or association in solution.

Q.79. What is the purpose of adding ethylene glycol to water?
Ans. Ethylene glycol (CH₂OHCH₂OH) is added to water to lower its freezing point. It is known as antifreeze solution.

Q.80. Why does the solubility of NaCl in water increase with the rise in temperature?
Ans. Because the process of dissolution is of endothermic nature.

Q.81. What is the effect of temperature on the molarity of a solution? 
Ans. It changes with the change in temperature.

Q.82. Can a solution of its own have osmotic pressure?
Ans. No, it can have only vapour pressure and not osmotic pressure.

Q.83. Two liquids A and B upon mixing form a warm solution. What type of deviations do they show from Raoult's Law?
Ans. Since energy is released in the form of heat when the two liquids A and B are mixed, they show negative deviation from Raoult's Law.

Q.84. What will happen when red blood corpuscles (RBCs) are placed in 
(a) 1 % NaCI solution 
(b) 0.6% NaCI solution?
Ans. We all know that RBCs are isotonic with 0.9% NaCI solution.
(a) If RBCs are placed in contact with 1 % NaCI solution, then the osmotic pressure of 1 % NaCI will be higher than that RBCs. As a result, water present inside the cell moves into the NaCI solution through cell walls acting as semi-permeable membrane. The RBCs will therefore, shrink.
(b) However, reverse will take place in case these are kept in contact with 0.6% NaCI solution which has less osmotic pressure. Water will now move into the RBCs and they will swell.

Q.85. What should be the maximum concentration of the solute in case a solution is to be ideal?
Ans. It should not be more than 5 % either W/W or W/V.

Q.86. What will the nature of the solid solution formed on mixing two solids with large difference in particle size?
Ans. The solution is known as interstitial solid solution.

Q.87. Which colligative property is generally used for determining the molar mass of a solute?
Ans. Osmotic pressure is generally used for this purpose.

Q.88. What is common in all the four colligative properties?
Ans. All of them depend upon the number of the particles of the solute in the solution as well as its molar concentration.

Q.89. Will osmosis take place when 0.1 M aqueous urea and glucose solutions are separated by semi permeable membrane?
Ans. No, it will not take place as they are isotonic as well as iso-osmotic in nature.

Q.90. The cryoscopic constant (K_f) for water is 1.86 K mol⁻¹kg⁻¹. What does it signify?
Ans. It signifies that when 1 mole of a normal solute is dissolved in one kg of water, the freezing point of water is lowered by 1.86 K.

Q.91. How does osmotic pressure depend upon temperature?
Ans. It increases with the rise in temperature (π = CRT).

Q.92. Which aqueous solution has higher concentration; 1 molar or 1 molal having the same solute?
Ans. In aqueous solution, the density of water is normally taken as one. This means that 1m solution has 1 mole of the solute dissolved in 1000 g or 1000 mL of water. At the same time, 1M solution contains 1 mole of the solute in 1000mL solution which is the volume of both the solute and the solvent present in the solution. This clearly shows that the solvent present in 1M solution is less as compared to 1 m solution. Therefore, 1M solution is more concentrated than 1 m solution.

Q.93. Why is molality of a solution preferred for expressing concentration over molarity?
Ans. In molality, the mass of the solvent is considered while in expressing molarity, volume of solution is taken into account. Since mass does not change with temperature while volume changes, molality does not change with temperature but molarity changes. Hence, molality is better for expressing the concentration of solution than molarity.

Q.94. Will elevation in boiling point temperature be same for 0⋅1 MNaCI and 0⋅1M sucrose solution?
Ans. No it will not be the same because colligative property does not depend upon molar concentration alone but also upon the number of particles (ions) in solution. Sodium chloride (NaCI) is an ionic solid and will form more number of particles (ions)in solution than sucrose (C₁₂H₂₂O₁₁) which is a molecular solid. Thus, the elevation in boiling point for 0.1 M NaCl solution will be more.

Q.95. What is the expected deviation from ideal solution behaviour when acetone and chloroform are mixed to form a solution?
Ans. The molecules of acetone and chloroform will get linked by intermolecular hydrogen bonding. This means that the volume of the solution will be less than for ideal solution. Therefore, ΔV_(mix) will be negative and solution will show negative deviation as compared to ideal solution.