Class 12 Chemistry

Chapter 2 - Solutions

(Magical Series) Very Important Questions Set 6

 

Q.1.     Calculate the boiling point elevation for a solution prepared by adding 10 g of CaCl₂ to 200 g of water. (K_b for water = 0.52 K kg mol^–1, molar mass of CaCl₂ = 111 g mol^–1)

[Ans: 0.2306 K]

Q.2.     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 –15.0 °C, what is the boiling point of the solution? (K_b = 0.52 K kg mol^-1 and K_f = 1.86 K kg mol^-1 for water)

[Ans: 377.19 K]

Q.3.     1.00 g of a non-electrolyte solute dissolved in 50 g of benzene lowered the freezing point of benzene by 0.40 K. The freezing point depression constant of benzene is 5.12 K kg mol^-1. Find the molar mass of the solute. 

[Ans: 256 g mol^–1]

Q.4.     A 5% solution (by mass) of cane-sugar in water has freezing point of 271 K. Calculate the freezing point of 5% solution (by mass) of glucose in water if the freezing point of pure water is 273.15 K. [Molecular masses: Glucose C₆H₁₂O₆: 180 amu; Cane-sugar C₁₂H₂₂O₁₁: 342 amu]

[Ans: 269.07 K]

Q.5.     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 °C while pure water boils at 100°C. What mass of glycerol was dissolved to make the solution? (K_b for water = 0.512 K kg mol^–1).  

[Ans: 37.73 g]

Q.6.     15.0 g of an unknown molecular material was dissolved in 450 g of water. The resulting solution was found to freeze at –0.34 °C. What is the molar mass of this material? (K_f or water = 1.86 K kg mol^-1).   

[Ans: 182.35 g mol^–1]

Q.7.     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 added to this solution. The new vapour pressure becomes 2.9 kPa at 298 K. Calculate

(i) the molecular mass of solute and

(ii) vapour pressure of water at 298 K.

[Ans: (i) 34 g mol^–1, (ii) 3.4 kPa]

Q.8.     Calculate the boiling point of a solution prepared by adding 15.00 g of NaCl to 250.00 g of water. (K_b for water = 0.512 K kg mol^–1. (Molar mass of NaCl = 58.44 g).

[Ans: 374.20 K]

Q.9.     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 a non-electrolyte, determine its molar mass.

[Ans: 14193.29 g mol^–1]

Q.10.     What would be the molar mass of a compound if 6.21 g of it dissolved in 24.0 g of chloroform to form 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, K_b for chloroform is 3.63 °C/m.   

[Ans: 148.15 g mol^–1]

 

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