Question

17. What is the volume of 1M acetic acid that needs to be added to 1L of 25mM sodium acetate solution to achieve pH of 5.5? Assume pka of 4.8 and the added acid to have negligible effect on volume. 18. For question 17 above, what will be the answer if concentration of sodium acetate in the initial 1L solution is 40mm? 19. What is the pH of a solution of 10-3 M HCI? Assume complete dissociation of hydrochloric acids to its respective ions.

Answer 1

17. Let 'V' litres of Im acetic acid be added Son initial [Acetic acid J = Initial volume X Molan'ty total volume = y x1= V M. -- Vt1 VH Similarly [sodium acetate) = 1 x 25 mm - VH = 25X163 M. TV1 According to hendesson- hasselbalch equation, To pH = plat log Lacelate] Acetic acid] → 5.5 = 4.8+ lege veters) V > on 10045 25x112 > __ 5.0119 = 25x10 3 v = = 0.004988 letree 4.988 oncl now, concenbatin of hodium acetate = Yomm 1 ses initial [sodium acetate]: 1 x yo mm VH VH10% 10

= 40x163 M_ VEL I and thitial to [ Acetic acid ů same ier VH So pH = pla t loo acetate Acetic acid 5.5 = 4. 8 t lo HA 109.7 yox 103 * v= 0.00798 = 7.98 L ml 19. [hu] = 103 m. Às & Hcie completely dissociated, (H+) = 10-3 m. - So pH = -log[447]