Question

A hydrocyanic acid buffer solution contains 0.84 M hydrocyanic acid (HCN) and 0.61 M of its conjugate base (CN). If a chemist adds 0.15 mol of nitric acid (HNO3), a strong acid, to 0.55 L of the buffer solution, what will be the final pH of the solution? (The pk of HCN is 9.21. Assume the volume of the added HNO3 is negligible.) 4.0

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Answer 1

The answer is given in the attachment.
Anorer pka of 9.21 0.462 mole HCN = x 0.55 L HON buffer solution contain 0.84 M Hen and o.61 M en in 0.55 L 0.55L buffer sohn mole of 0.84 finole) noot i mole) if on 15 mode Hoog is added, then it will protonate CNO ; CN-t HNO3 → (0.3355 -0.15) mole = 0.1855 mode. 0.3355 no 6 - 0.55 Laloob I mole Hat No 3 Now mole CN- - 0.612 mole (o 0.462 + 0.15) mole conc of ien- M ( 0:1855) 2016052 41 HCN - PH - phat log [cN- CHNY

+ pH=9.24 log 0.1855 .55 612 9.21 + + log (O.18 1855 12 9.21 0.52 8.69 4 0.15 wole HNO3 PH of buffer sohn after adding is 8969