CBSE Class 12 Chemistry Solutions Notes Set A

Solution

KEY CONCEPTS

Solution is the homogeneous mixture of two or more substances in which the components are uniformly distributed into each other. The substances which make the solution are called components. Most of the solutions are binary i.e., consists of two components out of which one is solute and other is solvent. Ternary solution consists of three components

Solute - The component of solution which is present in smaller quantity.

Solvent – The component of solution present in larger quantity or whose physical state is same as the physical state of resulting solution.

Types of solutions: Based on physical state of components solutions can be divided into 9 types.

Solubility - The amount of solute which can be dissolved in 100grm of solvent at particular temp. to make saturated solution.

Solid solutions are of 2 types -

1. Substitutional solid solution e.g. Brass (Components have almost similar size)

2. Interstitial solid solution e.g. steel (smaller component occupies the interstitial voids)

Expression of concentration of solution

1. Mass percentage= amount of solute present in 100grm solution.

For liquid solutions percentage by volume is expressed as = volume of solute(V_B) / volume of solution (V_A+V_B)*100

2. Mole fraction it is the ratio of no. of one component to the total no. of moles of all components. It is expressed as ‘x’. For two component system made of A and B ,X_A= n_A +n_B , X_B= n_A+n_B , Sum of all the components is 1 ; X_A+X_B =1

3. Molarity (M)= No.of moles solute/ volume of solution(L)

It decreases with increase in temperature as volume of solution increases with temperature.

4. Molality (m) =  no of moles of solute/ mass of solution(in kg)

No effect of change of temperature on molality as it is mass to mass ratio.

5. Normality (N) = no.of gram equivalent of solute/ volume of solution(L) 

It changes with changes temperature.

6. Parts per million (ppm) concentration of very dilute solution is expressed in ppm.

Ppm =W_B/W_B+W_A=10⁶

Vapor pressure – It is defined as the pressure exerted by the vapour of liquid over the liquid over the liquid in equilibrium with liquid at particular temperature vapour pressure of liquid depends upon nature of liquid and temperature.

Roult’s Law –

1. For the solution containing non-volatile solute the vapor pressure of the solution is directly proportional to the mole fraction of solvent at particular temperature

P_AœX_A

PA = P⁰_A.X_A

2. For the solution consisting of two miscible and volatile liquids the partial vapor pressure of each component is directly proportional to its own mole fraction in the solution at particular temperature.

PA=P⁰_A. XA ,   P_B=P⁰_B .X_B

And total vapor pressure is equal to sum of partial pressure. P_total = P_A + P_B

Ideal solution – The solution which obeys Roult’s law under all conditions of temperature and concentration and during the preparation of which there is no change in enthalpy and volume on mixing the component.

Conditions –
P_A = P⁰_A X_A,             P_B = P⁰_B.X_B
Mix = 0,                    mix = 0
This is only possible if A-B interaction is same as A-A and B-B interaction nearly ideal solution are –
1. Benzene and Toluene
2. Chlorobenzene and Bromobenzene
Very dilute solutions exhibit ideal behavior to greater extent.

Non-ideal solution –
(a) P_A ≠ P⁰_A.X_A                     (b) P_B ≠P⁰_B.X_B
(b)ΔH_mix ≠ 0                        (d)ΔV_mix ≠ 0
For non-ideal solution the A-B interaction is different from A-A and B-B interactions
i. For solution showing positive deviation
P_A > P⁰_A, PB > P⁰_B. X_B
ΔH_Mix = positive, ΔVmix=positive (A-B interaction is weaker than A-A and B-B )
E.g. alcohol and water

ii. For the solution showing negative deviation
P_A < P⁰_A.X_A,              P_B<P⁰_B.X_B
ΔH_Mix= negative,        ΔV_mix = negative’
A-B interaction is stronger than A-A and B-B interactions
E.g. Chloroform, acetone, HCl and water

What is Azeotrope? – The mixture of liquids at particular composition which has constant boiling point which behaves like a pure liquid and cannot be separated by simple distillation. Azeotropes are of two types:
(a) minimum boiling Azeotrope (mixture which shows +ve deviations ) ex. alcohol and water
(b) maximum boiling Azeotrope (which shows –ve deviations) ex. acetone and chloroform
Colligative Properties - Properties of ideal solution which depends upon no. of particles of solute but independent of the nature of particle are called colligative property

Relative lowering in vapour pressure:
                                                             (P^o_A – P_A )/ P^o_A = X_B

Determination of molar mass of solute
                                                     M_B =( W_A× M_A× P^o_A)/W_A×(P^o_A –P_A)

Elevator in Boiling Point
                                                               ΔT_B = K_b. m
                                                    Where ΔT _B = T’_B- T^o_B
                                                                 K_b = molal elevator constant
                                                                  M = molality
                                                                M_B =(K_b×1000×W_B)/ΔT_B×W_A

Depression in Freezing Point:
                                                               ΔT_f = k_f. m
                                                     Where ΔT_f – T’_f ; m = molality

                                                                K_f = molal depression constant
                                                             unit = k.kgmol^-1

Osmotic Pressure
The hydrostatic pressure which is developed on solution side due movement of solvent particles from lower concentration to higher concentration through semipermeable membrane denoted as π and it is expressed as

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