Solution Exercise - II

Page # 37 SOLUTION EXERCISE – II BOARD PROBLEMS Q.1 Mention a large scale use of the phenomenon called reverse osmosis. Q.2 Two elements A and B form compounds having molecular formula AB2 and AB4. When dissolved in 20 g of benzene, 1 g of AB2 lowers the freezing point by 2.3 K, whereas 1 g of AB4 lowers it by 1.3 K. The molar depression constant for benzene is 5.1 K kg/mol. Calculate the atomic masses of A and B. Q.3 State Henry's law about the solubility of a gas in a liquid. Q.4 What is the sum of the mole fractions of all the components in a three component system? Q.5 Define mole fraction of a component in a solution. Q.6 State the formula relating pressure of a gas with its mole fraction in a liquid solution in contact with it. Q.7 A solution is made by dissolving 30 g of non-volatile solute in 90 g of water. It has a vapour pressure of 2.8 KPa at 298 K. At 298 K, vapour pressure of pure water is 3.64 K Pa. Calculate the molar mass of the solute. Q.8 What would be the value of van't Hoff factor for a dilute solution of K2SO4 in water? Q.9 State Henry's law for solubility of a gas in a liquid. Explain the significance of Henry's law constant. At the same temperature, hydrogen is more soluble in water than helium. Which of them will have a higher value of KH and why? Q.10 Two liquids A and B boil at 145º C and 190ºC respectively. Which of them has a higher vapour pressure at 80ºC? Q.11 (a) Why is the vapour pressure of a soltuion of glucose in water lower than that of water? (b) A 6-90 M solution of KOH in water contains 30% by mass of kOH. Calculate the density of the KOH solutin. [Molar mass of KOH = 56 mol–1] Q.12 (a) Urea forms an ideal solution in water. Determine the vapour pressure of an aqueous solution containing 10% by mass of urea at 40ºC, (Pºs = 55.3 mm of Hg) (b) Why is freezing point depression of 0.1 M sodium chloride solution nearly twice that of 0.1 M glucose solution? Q.13 Define osmosis. Q.14 An antifreeze solution is prepared from 222.6 g of ethylene glycol and 200 g of water. calculate the molality of the solution, if the density of this solution be 1.072 g mol–1. What will be the molarity of the solution? Q.15. A 0.1539 molal aqueous solution of cane sugar (342) has a freezing point 271 K while the freezing point of pure water is 273.15 K. What will be the freezing point of an aqueous solution containing 5g of glucose (180) per 100 g of solution ? Q.16 Q.17 State Henry's Law correlating the pressure of a gas and its solubility in a solvent and mention two applications for the law. Calculate the temperature at which a solution containing 54 g of glucose (C6H12O6) in 250 g of water will freeze. (Kf for water = 1.86 k mol-1 kg ) Page # 38 SOLUTION Q.18 State Raoult's law for solutions of volatile liquids. Taking suitable examples explain teh meaning of positive and negative deviations from Raoult's law. Q.19 Define the term osmotic pressure. Describe how the molecular mass of a substance can be determined by method based on the measurement of osmotic pressure. Q.20 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 7.5"C ? The freezing point depression constant, Kf for water is 1.86 K kg mol–1. Assume van't Hoff factor for NaCl is 1.87. Q.21 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 solution? Q.22 (a) (i) (ii) (b) has an Q.23 (a) What is meant by : (i) Colligative propertion (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 25º C, a total pressure of 1 atmosphere and mole fraction of nitrogen in air of 0.78 [KH for nitrogen = 8.42 × 10–7 M/mm Hg] Q.24 What is meant by 'reverse osmosis'? Q.25 Differentiate between molarity and molality values for a solution. What is the effect of change in temperature on molarity and molality values? Q.26 A solution prepared by dissolving 8.95 mg of a gene fragement in 35.0 mL of water has an osmotic pressure of 0.335 torr at 25ºC. Assuming that the gene fragment is a non-electrolyte, calculate its molar mass. Q.27 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 7.5º C ? The freezing point depression constant, Kf, for water is 1.86 K kg mol–1 . Assume van't Hoff factor for NaCl is 1.87. Q.28 (a) Define the following terms: Mole fraction Van't Hoff factor 100 mg of a protein is dissolved in enough water to amke 10.0 mL of a solution. If this solution osmotic pressure of 13.3 mm Hg at 25ºC, what is the molar mass of protein? (R = 0.0821 L atm mol–1 K–1 and 760 mm Hg = 1 atm.) State Rault's law for a solution containing volatile components. How does Rault'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. (Kf for benzene = 5.12 K kg mol–1) OR (a) Define the following terms : (i) Ideal solution (ii) Azeotrope (iii) Osmotic pressure (b) A solution of glucose (C6H12O6) in water is labelled as 10% by weight. What would be the molality of the solution ? (Molar mass of glucose = 180 g mol–1)