4. An ideal solution contains 40 mole percent of A and 60 mole percent of B at 80 oC. The vapor pressure of pure A and B at this temperature are 480 torr and 890 torr, respectively. Calculate the vapor pressure of the solution.

Answer :  The vapor pressure of the solution is, 726 torr.

Explanation : Given,

Mole percent of A = 40 %

Mole fraction of A = 0.4

Mole percent of B = 60 %

Mole fraction of A = 0.6

Now we have to calculate the partial pressure of A and B.

According to the Raoult's law,

where,

= vapor pressure of gas

= vapor pressure of pure gas  

= mole fraction of gas

and,

Now we have to calculate the vapor pressure of the solution.

Thus, the vapor pressure of the solution is, 726 torr.

h let me think

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%