Grade 12Physical Chemistry
The pH of 0.004M hydrazine solution is 9.7. Calculate its ionization constant Kb and pKb ?
1 Answer
Supravat
NH2NH2 + H2O -----> NH2NH3+ + OH-From the given pH the Hion concentration can be measured.So, we have[H+] = antilog (–pH) = antilog (–9.7) = 1.67 × 10^-10Now, [OH-] = Kw / [H+] = 1 × 10^-14/1.67 × 10^-10 = 5.98 × 10^-5.The concentration of the corresponding hydrazine ion is also the same as that of hydroxyl ion. The concentration of both these ions is very small so the concentration of the undissociated base can be taken equal to 0.004 MThus, Kb= [NH2NH3+][OH-] / [NH2NH2]= (5.98 × 10^-5)^2/ 0.004 = 8.96 × 10^-7.So, pKb = –logKb = –log(8.96 × 10–7) = 6.04.
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