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# [Solved] CHE201 Assignment 2 Spring 2020

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20/07/2020 11:51 pm

CHE201 Physical Chemistry Assignment 2 Solution & Discussion Spring 2020

CHE201 assignment 2 Solution Idea:

Question No. 1

Give any four colligative properties of solutions?  (1.5×4)

Relative Lowering of vapor pressure:

This is colligative property depends upon the number of solute particles. It can define as vapor pressure of any solution with its liquid at the equilibrium can be lower by adding the non-volatile solute in the solution. It causes reduce the volatility of the solution which is due to non volatile solute.

Pi = Vapor pressure of the pure solvent

Xi = Mole fraction of the components of solution

Lower of vapor pressure is express from this equation

Dp  = p A    - p

Dp  = p A    (1 - xA  )

Dp  = p A  xB

In this equation the lower of vapor pressure is directly proportional to the mole fraction of the solute. It shows that greater the number of solute causes the lower of vapor pressure.

Boiling point elevation (ebullioscopy):

The elevation of boiling point is due to change in the vapor pressure of the solution. When non-volatile solute is added in the solution, it causes change in the vapor pressure of the solution. The boiling point of a pure solvent increases by the addition of a non-volatile solute and the elevation can be measured by ebullioscopy.

DT  = iKb m

• T= Change in temperature

i = Van't Hoff factor, which is the number of particles into which the solute dissociates

m = Molality, which is the moles of solute per kilograms of solvent Kb = Molal boiling point constant (for water Kb = 0.5121C/m)

Freezing point depression (cryoscopy):

The freezing point of pure solvent or solution can also depress due to present on-volatile solute in the pure solvent. The non-volatile solute changes in the freezing point of the liquid.

The freezing point of a pure solvent is lowered by the addition of a solute which is insoluble in the solid solvent and the measurement of this difference is called cryoscopy.

DT  = iK f m

• T= Change in temperature

i = Van't Hoff factor, which is the number of particles into which the solute dissociates m = Molality at which is the moles of solute per kilograms of solvent

Kb = Molal freezing point constant (for water Kf = 1.86 C/m)

Osmotic pressure:

The osmotic pressure of a solution is the difference in pressure between the solution and the pure liquid solvent when the two are in equilibrium across a semi-permeable membrane which allows the passage of solvent molecules but not of solute particles. It can also be change by addition of non-volatile solute in the solution and it causes change in the osmotic pressure of the solution.

 P = nRTi = cRTi \ c   = n V V

 Question No. 2 Describe Azeotropes with examples? (04)

Azeotropes can be defined as the mixture of two liquids which has constant boiling points and its composition dont change along with simple distillation technique.

This will be happen when an azeotrope is boiled; the vapour has the same proportions of constituents as the unboiled mixture and their composition are unchanged by distillation. Azeotropes are also called constant boiling point mixtures.

Examples:

1. An ethanol-water mixture is an example, on fractional distillation it can form by 95% of pure ethanol.
2. A mixture of Nitric acid and water is also an example, which contain 68% Nitric acid and 32% water which boils at 120
3. A mixture of Sulphuric acid 98.3% with water boils at 338
4. A mixture of perchloric acid (71.6%) with water boils at 203 °C.

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