A 40 ml solution of weak base BOH is tritrated with 0.1M HCL. pH is 10.04 and 9.14 after addition of 5 ml and 20 ml acid respectively. find out Kb for weak base.

Hi,Normality of base BOH is NbasepOH = pKb + logsaltbasei ) 14-10.04 =  pKb + log5 ×0.140 × Nbase -5 ×0.1ii) 14-9.14 =  pKb + log20×0.140 × Nbase - 20 ×0.1Equating the values of pKb from above two expression, we get3.96 - log5 ×0.140 × Nbase -5 ×0.1 = 4.86-log20×0.140 × Nbase - 20 ×0.1log20×0.140 × Nbase - 20 ×0.1×5 ×0.140 × Nbase -5 ×0.1 = 0.9440 × Nbase - 5 ×0.140 × Nbase -  20 ×0.1 = 7.943On solving above equation,  Nbase = 3.47239.44= 0.088 Substitute the value of  in equation 13.96 =  pKb + log5 ×0.140 ×0.088 -5 ×0.1pKb = 3.96  - log0.166 =3.96--0.78 = 4.74Kb =1.83 ×10-5Regards

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