Question

2. (32 points) Strychnine is a weak base with a pk of 5.74. A 150. mL sample of 0.076 M strychnine solution is titrated using 0.060 M hydrochloric acid. What is the pH of the solution at the following points: a) No acid has been added. b) 25.00 mL of acid have been added. c) 100.00 mL of acid have been added. d) The midpoint of the titration. e) The equivalence point of the titration. 1) Sketch this titration curve, labeling the axes, the equivalence point, the midpoint, and the buffer region.

Answer 1

3. Strychnine a weak base let's consider it ces BOH (Boh] = 0.076M, isome THI)=0.06m, ume MBOH = 11.ummol nHCl = (0.06 xv) mmd PKb =5.74 a) No cuid is added pure weak base DHE 14- [468%-dogc)]14-(£ (5-74-lego-076)] PH = 10:57] ane b) as me of HCl 7 nuci = 2580.06 > nHCl = 1.5 mino) BOH + HCl - BC1 + H2O initial 1-4 i 5 - 1.5 fined 9.9 Basic buffer par = 142 (prot long enough a 14-1574 blog :) PH=9.08 Ane c) Icome of HCI -- neesi = 100x0.06 =) 6mmol BOH + HCl - BCI + H2O initial 11- 4 6 fined su PH=14-(pkb+ leg (BC1] = 14-1 d sy |PM = 8.21 / Ane

d) cet mid point { n Bore = nHC1 = 4(11:4) = 0.06xV Ver = g5 me nHCl = 9580.06 = 5-7 mmol BOH + HCl - BCI + H2O initical 11.4 - 5.7 5 7 final 5.7 Butter PM = 10- [oks te lang ond) = 14- (sau a day 54) [PH = 8.26) Ana el at end point | h20H - PHU 9 (1-1) = 0:06 YV v=1gome n1C1 = 0.06x190) = 1.4 mmol BOH + HCL - Bcl + H2O initial 11.4 11.4 11.4 final Ceci] = 14,00 CBC1T = hliny pH = {(14-pkb-dayc) =(4-5.74- day 11-48340) PH=4.87] Ane 150 +190