The mass of a non-volatile solute (molar mass 40 g mol^–1) that should be dissolved in 114 g octane to reduce its vapour pressure to 80 % would be:

1. 6 g

2. 7 g

3. 8 g

4. 10 g

Benzene and toluene form an ideal solution over the entire range of composition. The vapour pressure of pure benzene and toluene at 300 K are 50.71 mm Hg and 32.06 mm Hg respectively.

The mole fraction of benzene in vapour phase, if 80 g of benzene is mixed with 100 g of toluene, would be:

1. 0.41

2. 0.68

3. 0.72

4. 0.59

The vapour pressure of 1 molal solution of a non-volatile solute in water at 300 K would be:

(The vapour pressure of water at 300 K = 12.3 kPa)

A solution containing 30 g of non-volatile solute in 90 g of water has a vapour pressure of 2.8 kPa at 298 K. Further, 18 g of water is then added to the solution and the new vapour pressure becomes 2.9 kPa at 298 K. The vapour pressure of water at 298 K will be:

1. 1.53 kPa

2. 2.53 kPa

3. 3.53 kPa

4. 4.53 kPa