Advertisements
Advertisements
Question
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.
Advertisements
Solution
Given: `P_A^0` = 450 mm Hg
`P_B^0` = 700 mm Hg
PTotal = 600 mm Hg
xA = ?
Applying Raoult’s law,
PA = `x_A xx P_A^0`
PB = `x_B xx P_B^0`
= `(1 - x_A)P_B^0`
PTotal = `P_A + P_B`
= `x_A xx P_A^0 + (1 - x_A)P_B^0`
= `P_B^0 + (P_A^0 - P_B^0)x_A`
Substituting the given values, we get
600 = 700 + (450 − 700)xA or 250xA = 100
or xA = `100/250` = 0.40
Thus, the composition of the liquid mixture will be
xA (mole fraction of A) = 0.40
xB (mole fraction of B) = 1 − 0.40 = 0.60
Calculation of composition in the vapour phase:
PA = `x_A xx P_A^0`
= 0.40 × 450 mm Hg
= 180 mm Hg
PB = `x_B xx P_B^0`
= 0.60 × 700 mm Hg
= 420 mm Hg
Mole fraction of A in the vapour phase = `(P_A)/(P_A + P_B)`
= ` 180/(180+420)`
= `180/600`
= 0.30
Mole fraction of B in the vapour phase = 1 − 0.30 = 0.70
APPEARS IN
RELATED QUESTIONS
In non-ideal solution, what type of deviation shows the formation of maximum boiling azeotropes?
State Raoult’s law for the solution containing volatile components
What is meant by positive deviations from Raoult's law? Give an example. What is the sign of ∆mixH for positive deviation?
What type of deviation is shown by a mixture of ethanol and acetone? Give reason.
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.
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 type of azeotrope is formed by positive deviation from Raoult’s law?
What is meant by negative deviation from Raoult's law? Give an example. What is the sign of ∆mixH for negative deviation?
Match the following:
| (i) | Colligative property | (a) | Polysaccharide |
| (ii) | Nicol prism | (b) | Osmotic pressure |
| (iii) | Activation energy | (c) | Aldol condensation |
| (iv) | Starch | (d) | Polarimeter |
| (v) | Acetaldehyde | (e) | Arrhenius equation |
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.
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]
Raoult’s law states that for a solution of volatile liquids the partial pressure of each component in the solution is ____________.
The boiling point of an azeotropic mixture of water and ethanol is less than that of water and ethanol. The mixture shows ____________.
The correct option for the value of vapour pressure of a solution at 45°C with benzene to octane in a molar ratio of 3 : 2 is
[At 45°C vapour pressure of benzene is 280 mm Hg and that of octane is 420 mm Hg. Assume Ideal gas]
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.
An azeotropic mixture of two liquids will have a boiling point lower than either of the two liquids when it ______.
