Numericals of Solution-Class 12

1)The boiling point of a solution containing 50g of a non-volatile solute in 1 kg of solvent is 0.5^o higher than that of the pure solvent. Determine the molecular mass of the solute. (Molecular mass of the solvent is 78 g/mol, K_b  for the solvent = 2.53 K m^-1)

Ans: 253 g/mol

2)On dissolving 3.24g of sulphur in 40g of benzene, boiling point of the solution was higher than that of benzene by 0.81 K. The molal elevation constant (K_b) for benzene is 2.53 K Kg/mol. What is the molecular formula of sulphur? (Atomic mass of sulphur is 32g/mol)

Ans: S₈

3)Calculate the boiling point of a solution containing 0.456 g of camphor ( molar mass = 152 g/mol) dissolved in 31.4 g of acetone (b.p= 329.45 K). Given that the molecular elevation constant per 100 g of solvents is 17.2 K.

Ans: 329.614 K

4)18 g of glucose is dissolved in 1 Kg of water. At what temperature will water boil under 1.013 bar pressure? Given K_b for water is 0.52 K kg mol^-1.

Ans: 373.052 K

5)0.70 g of an organic compound when dissolved in 32 g of acetone produces an elevation in boiling point of 0.25^O C. Calculate the molecular mass of the organic compound. ( K_b for acetone = 1.72 k Kg mol^-1)

Ans: 150.5 g/mol

6)0.90 g of a non-electrolyte was dissolved in 87.9 g of benzene. This raised the boiling point of benzene by 0.25^oC. If the molecular mass of the non-electrolyte is 103 g/mol, calculate the molal elevation constant for benzene.

Ans: 2.52 K kg mol^-1

7)Calculate the molal  elevation constant for water given that 0.2 molal solution of non-volatile and non-electrolyte solute increases the boiling point of water by 0.104 K.

Ans: 0.52 K Kg mol^-1

8)A solution containing 0.5126 g of naphthalene of molecular mass 128 g/ mol in 50 g of CCl₄ gave a boiling point elevation of 0.402 K while a solution of 0.6216 g unknown solute in the same mass of carbon tetrachloride gave a boiling point elevation of 0.647 K. Find the molar mass of the unknown solute.

Ans: 96.44 g mol^-1

9)A solution prepared by dissolving 1.25 g of methyl salicylate in 99 g of benzene has a boiling point of 80.31 ^oC. Determine the molar mass of this compound (b.p of pure benzene is 80.10 ^oC and K_b for benzene is 2.53 K Kg mol^-1.

Ans: 152.12 g/mol

10)What would be the molar mass of a compound if 6.21 g of it dissolved in 24 g of chloroform forms a solution that has a boiling point of 68.04^oC? Given that the boiling point of pure chloroform is 61.7^oC and K_b for chloroform is 3.63 Km^-1.

Ans: 148.15 g/mol

11)For a dilute solution containing 2.5 g of a non-volatile and non-electrolyte solute in 100 g of water, the elevation in boiling point at 1atm pressure is 2^oC. Assuming that the concentration of solute is much less lower than the concentration of the solvent, what is the vapour pressure of the solution? (K_b = 0.76 K kg mol^-1)

Ans:723.12 mm