UPSEE Solved Model Paper 3

pH = 9.26 shows that
[NH4OH] > HCl
∴ The mixture is a buffer
Let HCl = x mL = x mmol
∴ NH4OH = (300 - x) = (300 - x) m mol and NH4Clformed = x m mol NH4OH unreacted
pKb = 14 - 9.26 = 4.74
pOH = pKb + log

[NH4+]

[NH4OH]

4.74 = 4.74 + log

x

(300−2x)

x

300−2x

= 1
∴ x = 100 mL = Volume of HCl
300 - x = 200 mL = Volume of NH4OH
Hence,

Volume‌of‌N‌H4‌O‌H

Volume‌of‌H‌C‌l

=

200

100

=

2

1

or 2 : 1