Unit – III B

Problems on Lowering of Vapour Pressure:

  1. The vapour pressure of a solution containing 13 × 10-3 kg of solute in 0.1 kg of water at 298 K is 27.371 mm Hg. calculate the molar mass of the solute. Given that the vapour pressure of water at 298 K is 28.065 mm Hg. (94.63 g mol-1).
  2. The vapour pressure of pure benzene at a certain temperature is 640 mm Hg. A non-volatile solute of a mass 2.175 × 10-3 kg is added to 39.0 × 10-3 kg of benzene. The vapour pressure of a solution is 600 mm Hg. What is the molar mass of the solute? Given C= 12, H = 1. (69.6 g mol-1)
  3. A solution is prepared from 26.2 × 10-3 kg of an unknown substance and 112.0 × 10-3 kg acetone at 313 K. The vapour pressure of pure acetone at this temperature is 0.526 atm. Calculate the vapour pressure of solution if the molar mass of a substance is 273.52 × 10-3 kg mol-1. Given C = 12, H = 1, O = 16. (0.500 atm).
  4. In an experiment, 18.04 g of mannitol were dissolved in 100 g of water. The vapour pressure of water was lowered by 0.309 mm Hg from 17.535 mm Hg. Calculate the molar mass of mannitol. (184.3 g mol-1).
  5. The vapour pressure of water at 20 °C is 17 mm Hg. Calculate vapour pressure of a solution containing 2.8 g of urea (NH2CONH2)
  6. The vapour pressure of 2.1% solution of a non-electrolyte in water at 100 °C is 755 mm Hg. Calculate the molar mass of the solute. (58.69 g mol-1)

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