Question

1a:

19.930 g of a non-volatile solute is dissolved in 395.0 g of water.  
The solute does not react with water nor dissociate in solution.  
Assume that the resulting solution displays ideal Raoult's law behaviour.  
At 90°C the vapour pressure of the solution is 521.11 torr.  
The vapour pressure of pure water at 90°C is 525.80 torr.  
Calculate the molar mass of the solute (g/mol).

1b:

Now suppose, instead, that 19.930 g of a volatile solute is dissolved in 395.0 g of water.  
This solute also does not react with water nor dissociate in solution.  
The pure solute displays, at 90°C, a vapour pressure of 52.58 torr.  
Again, assume an ideal solution.  
If, at 90°C the vapour pressure of this solution is also 521.11 torr.  
Calculate the molar mass of this volatile solute.

1c:

The Henry's law constant (k_h) for O₂ in water at 20°C is 0.00128 mol/(L atm). How many grams of gas will dissolve in 2.01 L of H₂O in contact with pure O₂ at 2.09 atm?

1d:

The molecular weight of an organic compound was determined by measuring the freezing point depression of a benzene solution. A 0.500 g sample was dissolved in 50.0 g of benzene, and the resulting depression was 0.42°C (k_f (benzene) = 5.065°C/m). What is the approximate molecular weight of the compound?

Answer 1