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Question

Oswalds dilution law is applicable for both weak electrolytes and strong electrolytes- True or False?


A

True

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B

False

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Solution

The correct option is B

False


For a particular temperature, consider an aqueous solution of a weak electrolyte HA. In aqueous solution, HA remains in equilibrium with its ions.

HA+ H2O H++ A

Keq = [H+][A][HA][H2O]

Ka = Keq [H2O] = [H+][A][H2O]

If the initial concentration of HA is c M, and the degree of dissociation be α, then at equilibrium,

Ka = c α . cαc(1α) = cα21α

Throughout this chapter, whenever weak electrolytes are used, the value of α is very small. In this case, it can be approximated as 1- α 1

Hence K α = c α2 or α = Kαc

This is known as the Oswald's dilution law. It is strictly applicable only for weak electrolytes. You can't apply the above logic to strong electrolytes like HCl, HI, HClO4, NaOH, KOH etc

At infinite dilution, c 0 and 1 - α 0 or α 1

We can say that at infinite dilution, even weak electrolytes behave like strong ones - they dissociate almost completely. Experimental verifications reveal that this Oswald's law is applicable only for weak electrolytes.


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