`40mL` sample of `0.1M` solution of nitric acid is added to `20mL` of `0.3M` aqueous ammonia. What is the `pH` of the resulting solution?

Explanation

`{:(HNO_(3),+,NH_(3)rarr,NH_(4)NHO_(3),),(4mmol,,6mmol,4m mol,):}`
[Since `W_(B) (NH_(3))` is left and salt `(NH_(4)BO_(3))` is fored so it is a basic buffter]
Base left `= 6 - 4 = 2 mmol`
`["Acid"] = 40 xx 0.1 = 4 mmol`
`["Base"] = 20 xx 0.3 = 6 mmol`
`:. pOH = 4.7447 +log 4//2 = 5.0457` and
`pH = 14 - 5.0457 = 8.95`