Tamilnadu BoardEnglish MediumSTD 12ChemistryIonic Equilibrium3 Marks
Question
When the dilution increases by 100 times, the dissociation increases by 10 times. Justify this statement.
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Answer
(i). Let us consideran acid with $K _{ a }$ value $4 \times 10^4$. We are calculating the degree of dissociation of that acid at two different concentration $1 \times 10^{-2} M$ and $1 \times 10^{-4} M$ using Ostwalds dilution law $ \alpha=\sqrt{\frac{ K _{ a }}{ C }} $ (ii) For $1 \times 10^{-2} M$ acid, $\alpha=\sqrt{\frac{4 \times 10^{-4}}{1 \times 10^{-2}}}=\sqrt{4 \times 10^{-2}}=2 \times 10^{-1}=0.2$ (ii) For $1 \times 10^{-4} M$ acid, $\alpha=\sqrt{\frac{4 \times 10^{-4}}{1 \times 10^{-4}}}=\sqrt{4}=2$ (iv) i.e., when the dilution increases by 100 times (concentration decreases from $1 \times 10^{-2} M$ to 1 $\times 10^{-4} M$ ), the dissociation increases by 10 times. (v) When dilution increases, the degree of dissociation of weak electrolyte also increase. (Ostwalsd's dilution law).
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