Class 12 Chemistry Full Study Material For Boards Revision

7. Elevation in boiling point (ΔTb)
ΔTb = i.Kb m
where ΔTb = Tb – Tb°
Kb = molal boiling point elevation constant
m = molality of solution.

8. Depression in freezing point (ΔTf)
ΔTf = i.Kf m
where ΔTf = Tf° – Tf
Kf = molal depression constant
m = molality of solution.

9. Osmotic pressure (π) of a solution
πV = inRT or π = i CRT
where π = osmotic pressure in bar or atm
V = volume in litres
i = Van't Hoff factor
c = molar concentration in moles per litres
n = number of moles
T = Temperature on Kelvin Scale
R = 0.083 L bar mol^–1 K^–1
R = 0.0821 L atm mol^–1 K^–1

10. Van't Hoff factor (i)
i = Observed colligative property / Theoretically calculated colligative property
i = Normal molar mass / Abnormal molar mass

{i > 1 For dissociation of molecules
{i < 1 For association of molecules
{i= 1 For ideal solution

11. Relationship between relative lowering in vapour prescure and elevation in b.p.
Δb/pA°=(ixΔTb/Kb)MAx1000

Here
Δp is lowering in vapour pressure, pA° is vapour pressure of pure solvent, i is van't Hoff factor, ΔTb is elevation in boiling point, Kb is molal elevation constant and MA is molar mass of solvent

Electrochemistry
1. Conductivity (k)

K = 1 /P= 1/R =l/A= G G*/A

Where R is resistance, l/A = cell constant (G*) and 1/P is resistivity.

2. Relationship between k and Am

Am = 1000 kxc

Where m L is molar conductance, k is conductivity and C is molar concentration.

Kohlrausch’s law
(a) In general if an electrolyte on dissociation gives ν+ cations and γ– anions then, its limiting molar conductivity is given by 

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