Is the pH at the equivalence point in the titration of 0.10 M (CH3)2NH with 0.10 M HCl acidic, basic, or neutral
Dimethylamine is a weak base and HCl is a strong acid.
they react as :
(CH3)2NH + HCl (CH3)2NH2+ + Cl-
Kb for (CH3)2NH = 7.4 x 10-4 at 25 C
pKb = 3.13
so 0.10 M HCl will react with 0.10 M moles of (CH3)2NH to produce (0.10 / 2 = ) 0.05 M of (CH3)2NH2+
so we cannot use buffer equation as above as now no (CH3)2NH is left and all (CH3)2NH is converted into (CH3)2NH2+.
using hydrolisis equation for a salt of weak base and strong acid ...
pH = 1/2 [pKw - pKb - log c ]
pH = 1/2 [ 14 – 3.13 - log 0.05 ]
pH = 1/2 [ 10.87 - 1.3 ]
pH = 1/2 [ 9.57 ]
pH = 4.785
It will be acidic.
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