Class 11 Chemistry Chapter 9 Notes
Important Complete Computerized Class 11 Chemistry Chapter 9 Notes written by Professor Mr. Faraz Qadir Suib. These notes are very helpful in the preparation of Solutions of Class 11 Chemistry Chapter 9 Notes for the students of the intermediate and these are according to the paper patterns of all Punjab boards.
Summary and Contents:
Topics which are discussed in the notes are given below:
- Phenol-Water System
- Effect of temperature
- State of Raoult’s Law with its Mathematical expression: Raoult’s law can be applied to understand the relationship between mole fractions of two volatile components
and their vapour pressures before making the solution and after making the solution.
Explanation
Consider two liquids ‘A’ and ‘B’ with vapour pressures p°A and p°B in the pure state at a given temperature.
After making the solution, the vapour pressures of both liquids are changed. Let the vapour pressures of these
liquids in solution state be pA and pB with their mole fractions xA and xB, respectively. The liquid A is low
boiling and B is high boiling.
- Factors affecting relative lowering of vapour pressure
- Raoult’s Law (when both components are volatile)
- Explanation of graph
- Fractional Distillation of Ideal Mixture of Two Liquids
- Explanation of graph: The upper curve represents the composition of the vapours of different solutions while the lower curve
represents the composition of the liquid mixtures.
Reason
At any temperature the composition of vapours is different from the composition of liquid mixture.
• The point G is the boiling point of solution corresponding to composition I. It meets liquid curve at point
H and the vapour curve at point C.
- The composition of liquid mixture corresponding to point H is shown by point I. At point I the mixture
has greater percentage of B and less percentage of A. At the same temperature the vapours of the
mixture have the composition K.
• At point K, the percentage of A is comparatively greater than B when we compare it with composition
of liquid mixture corresponding to point I. Because A is a low boiling liquid it is present in the vapour
state in greater percentage than at point I.
- If the temperature of the mixture is maintained corresponding to point G the distillate will have greater
percentage of A and the residue will have greater percentage of B.
Reason
The fraction going to distillate is that which is in vapour state and it has greater % of A.
• The distillate of composition K is again subjected to distillation. Its boiling point is X and at this
temperature the distillate of composition Z is obtained.
• This distillate of composition Z is further distilled. The distillate becomes richer in A and residue is
more and more rich in B.
• Process of distillation is repeated to get the pure component A.
- We can completely separate the components by fractional distillation.
Zeotropic mixtures
Such liquid mixtures, which distil with a change in composition, are called zeotropic mixtures.
Example
Methyl alcohol-water solution can be separated into pure components by distillation.
- Why solutions deviate from Raoult’s law
- solubility and solubility curves: Whenever a solute is put in a solvent then the molecules or ions break away from the surface of the solid and
pass into the solvent to give a uniform solution. Some of the particles of the solute may come back towards the
solid due to collisions. This is called re-crystallization or precipitation.
- Explanation through Raoult’s law
- Calculation of number of moles
- Calculation of Molecular mass of solute
- Reason for the elevation of boiling point
- Graph for determination of vapour pressure
- Measurement of Boiling Point Elevation: Landsberger’s Method
- Measurement of Freezing Point Depression: Beckmann’s Freezing Point Apparatus
- Solutions of Numerical of Ch 9 Solutions Chemistry Class 11 Notes