Solutions Chemistry Class 12 notes - Online Notes

 

"Solutions" -  chemistry class 12 notes with pdf


Introduction:

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Notes :

• Mass Percent or percent by mass :- It is defined as the amount of solute in gram present in 100 grams of the solution.

Mass percentage of solute =
 (Mass of solute)/(mass of solutions) × 100%


• Mole Fraction (x) :- It is defined as the ratio of number of moles of one component to the total number of moles of the solution.
It is denoted by x.

xA +xB = 1 
( where A & B are two component)

xA = nA/(nA +nB )
Where
number of moles, 
n= Given Mass(W) / Molar Mass (M)


• Molality (m) :- It is defined as number of moles of solute dissolved in 1 kg(1000g) of the solvent. It is denoted by 'm'.

Molality,
 (m) = no. of moles of solute /mass of solvent(in kg)


• Molarity (M):- It is defined as the number of moles of solute per litre of solution.

Molarity ,
(M)= No. of moles of solute/ no. of litre of solution


★ Relationship Between Molarity (M) and Molality(m)

m = (1000×M)/(1000×d - M×MB)
Here,
MB = molar mass of solute
M = Molarity
m = Molality
d = density of solution in g/mol

M = (mass% × density × 10)/(molar mass of solute)

.i.e.    M = (x × d × 10)/MB


• Parts per million :-  Parts by weight of solute dissolved in parts by weight of 1 million of solutions.

ppm   =    (parts by weight of solute) / (Total mass of solution) × 1000000

Unit  ➡️  No unit


• Normality :-  Number of gram equivalent of solute dissolved in per litre of solution is called normality.

N  =  (number of gram equivalent of solute)/ (Total volume of solution)

Unit  ➡️  g eq. /L


★ Relationship Between Normality and Molarity :-

N × Equivalent mass = Molar mass × M

• Solubility :-
Maximum amount of solute dissolved in 100 g of solvent is called solubility.


OR
Rate of dissolving the substance in particular solvent is called solubility.

Factors of Solubility are :-
1) Temperature
2) Pressure




★ Henry's Law :-

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

p = KH × x 
Where
x = Mole fraction of a gas in solution
p = partial pressure of the gas
KH is called a Henry's law constant


_____________

Limitations of Henry's law :-

Henry's law holds good if the following conditions are fulfilled :-
i) The pressure is not too high
ii) The temperature is not too low.
iii) The gas do not chemically combine with the solvent.
______________


■ Raoult's Law :-

1) For solution containing non - volatile solution :

" The Vapour pressure of a solution containing non - volatile solution proportional to the mole fraction of the solvent."
PA = P°A xA

2) For binary Solution of volatile liquid :

"The Vapour pressure of the volatile component is directly proportional to the mole fraction of that component."
PTotal = PA + PB
PA = P°A × xA   &   PB = P°B × xB


_______________

Important :

★ Azeotropes :-

Azeotropes are the mixture of liquids which boil at constant temperature like a pure liquid without under going any change in the composition.
Azeotropes are also called " Constant Boiling Azeotropes ".

Types of Azeotropes 

a) Minimum Boiling Azeotropes

1. These are formed by those liquid pairs which show a positive deviation from ideal behaviour.
2. Such Azeotropes have boiling point lower than either of the component.

b) Maximum boiling Azeotropes

1. These are formed by those liquid pairs which show a negative deviation from ideal behaviour.
2. Such Azeotropes have boiling point higher than either of components.
_______________


✓Important :

★ Ideal Solution

1) Obey Raoult's law at every range of concentration.
2) A....A interaction, B....B interaction, A...B interaction should be same  i.e. 'A' and 'B' are identical in shape, size and character.
3) ∆H min = 0
Neither heat is evolved nor absorbed during dissolution.
4) ∆V min = 0
Total volume of solution is equal to sum of volume of each component.
5) P = PA + PB = P°A × xA + P°B × xB 


Non - Ideal Solution


Types :

A) Positive Deviation

1. Don't obey Raoult's Law.
2. A....B interaction is weaker than A...A and B...B interaction attractive force. 'A' and 'B' have different shapes, size and character.
3. ∆H min > 0 , Endothermic
Heat is absorbed.
4. ∆V min >0 , volume is increased after dissolution.
5. PA > P°A × xA  &  PB > P°B × xB

B) Negative Deviation

1. Don't obey Raoult's Law.
2. A....B attractive force should be stronger (greater) than A...A and B...B attractive forces. 'A' & ' B' have different shapes size  and character.
3. ∆H min < 0 , exothermic
Heat is evolved.
4. ∆V min < 0 volume is decreased during dissolution.
5. PA < P°A × xA   &    PB < P°B × xB
i.e. PA + PB < P°A × xA + P°A × xB
_______________

■ Colligative Properties

Dilute solutions containing a non - volatile solute exhibit some special properties which depend only upon the number of solute particles present in the solution irrespective of their nature.

Colligative Properties are :-
1) Lowering in vapour pressure.
2) Elevation in Boling point.
3) Depression in freezing point.
4) Osmotic pressure.

Let's see these properties in details.

1) Relative lowering in vapour pressure is equal to mole fraction of the solute in a dilute solution.

∆P / P°  = nB /(nA + nB)


2) Elevation in boiling point :

∆Tb = Tb - T°b    where, 
Tb = Boiling point of the solution
T°b = Boiling point of pure solvent

∆Tb = Kb × m    where 
Kb(molal elevation 
constant or ebullioscopic 
constant) = ∆Tb  if m = 1

*** Molal Elevation Constant may be defined as the elevation in boiling point when the Molality of the solution is unity.

∆Tb = Kb × WB/(MB × WA{in kg})


3) Depression in Freezing point :

∆Tf = T°f - Tf   where ,
Tf = freezing point of solution 
T°f = freezing point of solvent.

Or ∆Tf = Kf × m    where ,
Kf = molal depression constant 
(which is defined as Kf = ∆ Tf if m= 1)


4) Osmosis :

The spontaneous flow of solvent molecule through semi - permeable membrane from a pure solvent to a solution from a dilute to a concentrated solution.


__________________

Q) Differentiate between Diffusion And Osmosis ?

Ans:-
● Diffusion
1) No semi - permeable membrane is required.
2) In diffusion both solvent and solute molecules move.
3) Diffusion can not be stopped.
4) It is common in liquid as well as gas.

● Osmosis
1) Semi - permeable membrane is required.
2) It involves the movement of solvent molecules only.
3) Osmosis can be stopped.
4) It is common in liquid only.

__________________


★ Osmotic Pressure :-

The hydrostatic pressure built upon the solution which just stops the osmosis.

OR
The external pressure which must be applied on the solution in order to stop the flow of the solvent into the solution through a semi - permeable membrane is equal to Osmotic Pressure.


◆ Hypotonic :- A Solution of low Osmotic pressure is termed as Hypotonic.

◆ Hypertonic :- A Solution of high Osmotic pressure is termed as Hypertonic.

◆ Isotonic :- Solution having same Osmotic pressure are termed as isotonic.

◆ Endo-Osmosis :- When Water Molecules enter the cell.

◆ Exosmosis :- When Water Molecules go out of the cell.




■ Van't Hoff introduced a factor 'i'

i = Abnormal or observed Colligative Properties / Normal Colligative property
Or 
i = Normal Molecular mass / Observed molecular mass
Or  
i = no. of particles present in solution after association or dissociation / no. of particles present in solution before association or dissociation

if i = 1 , There is no association or dissociation of solute in the solution

If i > 1 , There is dissociation of solute in the solution.

& If i < 1 , There is association of solute in the solution.

And with this your chapter ends. 🤗And I hope that this notes might have helped you.

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