Calculate the pH of 0.1M ethylenediamine.



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Ethylene diamine is a diacidic base, the first ionisation of which is quite feasible. Relevant Kb values are 8.0EXP-5 (K1) and 9.0EXP-8 (K2). It is apparent that consideration of first ionisation is sufficient in order to calculate the pH of its aqueous solution. Now from the dissociation of a weak base we get [OH-] = square root (Kb*Cm)  here, for 0.1M soln. [OH-] = square root (8.0EXP-5*0.1) = 0.00283  or, pOH = -log 0.00283 = 2.5, hence pH = 14-2.5 = 11.5 (answer).

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