Advertisements
Advertisements
Question
100 g of liquid A (molar mass 140 g mol−1) was dissolved in 1000 g of liquid B (molar mass 180 g mol−1). The vapour pressure of pure liquid B was found to be 500 torr. Calculate the vapour pressure of pure liquid A and its vapour pressure in the solution if the total vapour pressure of the solution is 475 Torr.
Solution
Number of moles of liquid A, nA = `100/140 "mol"`
= 0.714 mol
Number of moles of liquid B, nB = `1000/180 "mol"`
= 5.556 mol
Then, the mole fraction of A, xA = `"n"_"A"/("n"_"A"+"n"_"B")`
= `0.714/(0.714+5.556)`
= 0.114
And, mole fraction of B, xB = 1 − 0.114 = 0.886
Vapour pressure of pure liquid B, `"p"_"B"^0` = 500 torr
Therefore, the vapour pressure of liquid B in the solution,
pB = `"p"_"B"^0"x"_"B"`
= 500 × 0.886
= 443 torr
Total vapour pressure of the solution, ptotal = 475 torr
∴ Vapour pressure of liquid A in the solution,
pA = ptotal − pB
= 475 − 443
= 32 torr
Now,
pA = `"p"_"A"^0"x"_"A"`
`=>"p"_"A"^0 = "p"_"A"/"x"_"A"`
= `32/0.114`
= 280.7 torr
Hence, the vapour pressure of pure liquid A is 280.7 torr.
APPEARS IN
RELATED QUESTIONS
What is meant by positive deviations from Raoult's law? Give an example. What is the sign of ∆mixH for positive deviation?
Define azeotropes.
The vapour pressures of pure liquids A and B are 450 and 700 mm Hg respectively, at 350 K. Find out the composition of the liquid mixture if the total vapour pressure is 600 mm Hg. Also, find the composition of the vapour phase.
Vapour pressure of pure water at 298 K is 23.8 mm Hg. 50 g of urea (NH2CONH2) is dissolved in 850 g of water. Calculate the vapour pressure of water for this solution and its relative lowering.
An aqueous solution of 2% non-volatile solute exerts a pressure of 1.004 bar at the normal boiling point of the solvent. What is the molar mass of the solute?
A solution containing 30 g of non-volatile solute exactly 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. Calculate:
- molar mass of the solute
- vapour pressure of water at 298 K.
What is meant by negative deviation from Raoult's law? Give an example. What is the sign of ∆mixH for negative deviation?
A solution containing 8.44 g of sucrose in 100 g of water has a vapour pressure 4.56 mm of Hg at 273 K. If the vapour pressure of pure water is 4.58 mm of Hg at the same temperature, calculate the molecular weight of sucrose.
Define Raoult’s law for the elevation of the boiling point of a solution.
What will be the vapour pressure of a solution containing 5 moles of sucrose (C12H22O11) in 1 kg of water, if the vapour pressure of pure water is 4.57 mm of Hg? [C = 12, H = 1, O = 16]
State Raoult’s law for a solution containing volatile components. Write two characteristics of the solution which obey Raoult’s law at all concentrations.
Raoult’s law states that for a solution of volatile liquids the partial pressure of each component in the solution is ____________.
Minimum boiling azeotrope is formed by the solution which showed
An aqueous solution of hydrochloric acid:
Considering the formation, breaking and strength of hydrogen bond, predict which of the following mixtures will show a positive deviation from Raoult’s law?
A solution of a non-volatile solute in water freezes at −0.30°C. The vapour pressure of pure water at 298 K is 23.51 mm Hg and Kf for water is 1.86 degree/mol. The vapour pressure of rain solution at 298 K is ______ mm Hg.
