Short Notes on Chapter 2 => Solution 12th CLASS

These are Short Notes on Chapter 2 => Solution 12th CLASS :

A solution may be defined as a Homogeneous mixtures of a single phase containing one or more of the chemical species dispersed on a molecular scale.

SOLUTE AND SOLVENT

(a) The component whose physical state is same as that of resulting solution is called as Solvent and the other component whose physical state changes is termed as Solute.
 e.g. In a homogenous mixture of Na(s) and Hg(l) resulting in the formation of NaHg(s), Na(s) is considered as solvent and Hg(l) is termed as Solute which is contrary to the common belief that liquids are solvents.

(b) When both components are having the same phase as that of that the resulting solution and the relative amount of one substance in a solution is much greater than that of the other, the substance present in greater amount is generally regarded as the solvent.

METHODS OF EXPRESSING CONCENTRATIONS OF SOLUTIONS:

The concentration of solutions are generally expressed in the following ways: Solute: designated as ‘b’ Solvent:

designated as ‘a’

1.             Molarity (M) : No. of moles of solute per litre of solution.

  Molarity = (No. Of Moles of b )  / (Volume of Solution in Ltr )

where V is in mL and   No. of moles of b = ( Mass in gram / Molar mass of b)

      2.             Molality (m) : No. of moles of solute per kg of solvent.

Molality =   (No. of moles of b ) / ( Mass of Solute in Kg)

3.             Normality (N) : No. of Gram equivalent of solute per litre of solution.

Normality  =  ( weight of solute) / (Equivalent Mass of Solute) 

where Equivalent Mass of Solute =  (Molar Mass) / ( n factor)

N = M × n_f : Where M is the molarity and n_f = n factor

4.         Mole fraction (X) : Ratio of number of moles of one of the components to the total number of moles present in the solution.

Mole Fraction = ( Moles of  Solute or Solvent) / (Total Moles of Solute and Solvent)

Total mole fraction of a solution is X_a + X_b  = 1.

5. Mass Percentage (w/W %) = 

[ (Mass of Solute  ) / ( Mass of Solution in g) ] x (100) 

_{A 10% aqueous NaCl solution contains 10 grams} 

of NaCl per 100 grams of solution. Ten grams of NaCl is mixed with 90 grams of water to form 100 grams of solution.

6. Volume Percentage (v/V %) = 

[ ( Volume of Solute) / Volume of Solution(ml)] x 100

e.g. 10% volume percentage of aqueous solution of ethanol means 10 mL solute present in 100mL of the solution.

7. Mass by Volume Percentage (w/V%) =  [ ( Mass of Solute(g) ) ] / (Volume of solution (mL) ] x 100

8. Parts per Million  (ppm) 
= [  ( No. of Parts of the componant )  /  No. of parts of all the componants of the solution ) ] x  10⁶

Concentration in parts per million can also be expressed as mass to mass, volume to volume and mass to volume.

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

Raoult’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_{A directly proportional to}  X_A

P_A =   (  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.

P_A=   (  P⁰_{A  )}  (  X_{A ),}          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 Raoult’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

ΔH _Mix = 0,        ΔV _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

ΔH _Mix ≠ 0,        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,     P_B> P⁰_B. X_B

ΔH _Mix = +ve,        ΔV _Mix = +ve

(A-B interaction is weaker than A-A and B-B )
E.g. alcohol and water


ii. For the solution showing negative deviation