SOLUTIONS NOTES : 12th Chemistry Chapter 2 : Maharashtra State Board New Syllabus

Notes, Imp Points, Formulae ,etc.

of 12th chemistry chapter 2 solutions based on HSC Syllabus (NEW)

Introduction :

Recall -

Mixture : It is a combination of two or more substances.

Mixtures are :-

(a) Homogeneous : Mixing of components is uniform.

(b) Heterogeneous : Non-Uniform mixing of components.

Classification of Homogeneous Mixtures :-

1) Colloids                                  2) True Solutions

DEFINITION OF

Solution: The solution is a homogeneous mixture of two or more pure substances.

TYPES OF SOLUTIONS 

There are total of 9 Types of Solutions :-

Capacity of Solution to Dissolve Solute 

Definition of 

Saturated Solution : It is the solution which contains maximum amount of solute dissolved in a given amount of solvent at a given temperature. 

(Equilibrium can be formed)

Super Saturated Solution : A Solution containing greater than equilibrium amount of solute is said to be super saturated solution.

(Unstable Solution)

Solubility : 

Definition : The solubility of a solute is its amount per unit volume of a saturated solution at a specific temperature.

FACTORS AFFECTING SOLUBILTY

Solubility depends on the nature of solute and solvent, temperature and pressure.

1) Nature of Solute and Solvent :-

LIKE DISSOLVES LIKE 

• Polar solutes dissolve in polar solvents. (NaCl in Water)
• Non polar organic compounds dissolves in nonpolar solvents . (Cholesterol in benzene)

The substances having similar intermolecular forces are likely to be soluble in each other.

2) Effect of temperature on solubility :

• In endothermic process, when temperature is increased , the solubility of substance increases. (KCl in Water )
• In Exothermic process, the solubility decreases with increase in temperature. (CaCl2 in water)
• Solubility of gases decrease with increase in temperature

NOTE : There is no direct correlation between solubility and exothermicity  and endothermicity.

2) Effect of pressure on solubility :

• Pressure has no effect on the solubilities of solids and liquids as they are incompressible.
• The solubility of gases increases with increasing pressure.

THE QUANTITATIVE RELATIONSHIP IS GIVEN BY HENRY'S LAW

Henry's Law :- 

It states that the solubility of a gas in a liquid is directly proportional to the pressure of gas over the solution.

S - Solubility of the gas in mol/L

P - Pressure of the gas in bar over the solution.

Kh - The proportionality constant is called Henry's Law Constant.

Exceptions to Henry's Law 

Gases like NH3 and CO2 do not obey Henry's Law. 
Reason : Because these gases react with water.

This is the reason why these gases have higher solubilities than expected by henry's law.

2.5 Vapour pressure of solutions of liquids in liquids

Raoult’s law : It states that the partial vapour pressure of any volatile component of

a solution is equal to the vapour pressure of the pure component multiplied by its mole fraction in the solution.

Suppose that for a binary solution of two volatile liquids A1 and A2 , partial pressures p1 and p2 and their mole fractions x1 and x2 respectively.

Composition of Vapour Phase:

 To find composition of vapour,

Let y1 and y2 be mole fractions of two components in vapour, p1 and p2 are their partial pressures and P is total vapour pressure.

then,

p1 = y1p    p2 = y2p

2.5.2 Ideal and nonideal solutions

1. Ideal solutions

i. Ideal solutions obey Raoult’s law over entire range of concentrations.

ii. No heat is evolved or absorbed when two components forming an ideal solution are

mixed. Thus, the enthalpy of mixing is zero. ∆mix H = 0

iii. There is no volume change when two components forming an ideal solution are

mixed. Thus volume of an ideal solution is equal to the sum of volumes of two

components taken for mixing. ∆mix V = 0

iv. In an ideal solution solvent-solute, solute- solute and solvent-solvent interactions are comparable.

v. The vapour pressure of ideal solution always lies between vapour pressures of

pure components.

2. Nonideal solutions

i. These solutions do not obey Raoult’s law over the entire range of concentrations.

ii. The vapour pressures of these solutions can be higher or lower than those of pure

components.

iii. Deviation from the Raoult's law : These solutions show two types of deviation

from the Raoult's law.

A. Positive deviations from Raoult's Law

Positive Deviation : Vapour pressure of solution greater than those of pure components.

Condition : Solute-solvent intermolecular attractions weaker than solute-solute and solvent-solvent intermolecular attractions.

Example : 

The solutions of ethanol and acetone, carbon disulphide and acetone

B. Negative Deviations from Raoult's Law

Negative Deviation : Vapour pressure of solution smaller than those of pure components.

Condition : Solute-solvent intermolecular attractions stroger than  solute-solute and solvent-solvent intermolecular attractions.

Example : 

The solutions of phenol and aniline, chloroform and acetone

2.6 Colligative properties of nonelectrolyte solutions :

Colligative Property : The physical properties of solutions that depend on the number of solute particles in solutions and not on their nature are called

colligative properties.

These are

1. vapour pressure lowering

2. boiling point elevation

3. freezing point depression

4. osmotic pressure

Non electrolyte solutions with Concentration 0.2M or less are considered.

2.7 Vapour pressure lowering :