**Ostwald dilution law**

source : slide player.com

Ostwald dilution law is an application of law of mass action for dissociation equilibrium of weak electrolyte. Consider a weak binary electrolyte,

AB <——> A^{+} + B^{–}

(Weak Electrolyte)

Moles before dissociation (t=0) 1 0 0

Moles after dissociation (At time ‘t’) 1-α α α

α is degree of dissociation of weak electrolyte ‘AB’ & ‘C’ is the concentration of AB in mole/litre then

[AB] = C(1–α)

[A^{+}] = Cα

[B^{–}] = Cα

At equilibrium

kα = [A^{+}] [B^{+}]/[AB] = (Cα)*(Cα)/C(1-α)

kα =Cα*α/(1-α)

Ka= dissociation constt. of ‘AB’

For weak electrolyte, α<<<1

So 1–α

Ka=Cα^{2}

α=ka/c =ka.V

“Degree of dissociation of weak electrolyte is directly proportional to square root of dilution.”

__Limitations of ostwald Dilution Law-__

- This law is applicable only for weak electrolyte
- This law is not applicable for strong electrolytes because strong electrolytes completely ionize at all dilution.