As the concentration of a solution increases, its vapor pressure decreases. For
ID: 575652 • Letter: A
Question
As the concentration of a solution increases, its vapor pressure decreases. For a nonvolatile solute B in a liquid solvent A, the relationship between concentration and vapor pressure is expressed by Raoult's law:
PA=XAPA
where PA is the vapor pressure of the solution, XAis the mole fraction of solvent, and PA is the vapor pressure of the pure solvent.
In a two-component solution consisting of A and B, the mole fraction, X, of component A is defined as
XA=moles Amoles A + moles B
1. A solution is composed of 1.60 mol cyclohexane (Pcy=97.6 torr) and 2.90 molacetone (Pac=229.5 torr). What is the total vapor pressure Ptotal above this solution?
Explanation / Answer
According to question -
No. of moles of Cyclohexane = 1.60 mol and Pcyo = 97.6 torr
No. of moles of Acetone = 2.90 mol and Paco = 229.5 torr
Now in the two component mixture of solution,
Total amount of components = (1.60+2.90) mol = 4.5 mol
Hence mole fraction of Cyclohexane (Xcy)= (1.60/4.5) = 0.355
and mole fraction of Acetone (Xac)= (2.9/4.5) = 0.644
Hence partial vapour pressure of cyclohexane, Pcy = Xcy* Pcyo = (0.355*97.6) torr = 34.6 torr
and partial vapour pressure of acetone, Pac = Xac* Paco = (0.644*229.5) torr = 147.8 torr
Therefore total vapour pressure = (34.6+147.8) torr = 182.4 torr
The end
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