Question

Calculate the pH for each of the cases in the titration of 25.0 mL of 0.100 M pyridine, C5H5N(aq) with 0.100 M HBr(aq) .

A. before addition of any HBr B. after addition of 12.5 mL of HBr C. after addition of 23.0 mL of HBr D. after addition of 25.0 mL of HBr E. after addition of 31.0 mL of HBr

Answer 1

CHENKG = 1.78109 pkb = -log Kb = -log (1-7 X10 9) = 8.77 ① stav +H2O - SHa Nit + oH I 01 - CL to * - X * E 0.1-X Kb = Easts Wh] 20H LAND 2 o.1-x=84 x - For weak base 1-7X10 9 = 0-1-X 1-7X10 9 = x= [OH-] = 1.78189 xao = 0.0000 130384 polt = -10g 2014] = log (0.0000 130 384)=4.885 pH = 14-polt = 14-4.885= 9.115

CH_N= Molarity = 0.1M | Hor: Mohrity = 0-1M 1 ② HBr molarity=0-IM volume=25m/=0.0252 volume = 12.5m1=0.012541 volume=23m1 = 0.0232 no ot molts 0-1 X 0-01251 no of moles = 0.18 0.023=0.0023 no of moles=0.0025 -0.00125 ÇHAN + HBr - GH NHIB e H.N+ ABr H, NHBS Io.0025 0.0023 o I-0.0023 I to-0023 I I 0.0025 0.00125 1 o to.0002 o 0-0023 -0.00125 +0.00125 o.00125 o Total volume = 0.025+ 0-0 230.0482 10.00125 Total volume = 0.025+ 0.0125=0.03752 -0.004167M -0-02 ] < - 0.00 T o [HgN] = h { HgN] = 2/2 = 0.0002 0.048 0-00123 u n [HU] = [cstts-WH Qn] = 0-0023 -0.04792 M 0.048 [esitaNHBR > 0.0375 0.00125 = 0.0333M 0-0375 [cs#_N86*3 = 0 pota pkb tlog - sity-NH133] Oh pleblog { HEN] [sitsiv port_8-77 +10g 04142 = 9-83|| pH = 14-polt - 14-9-831= 4.169 0.004167 pOH = 8-777109 0233 = 8.77 pt=14 - polt= 14-8-77=5.23

( HBr. Molarity = 0.19 volume=25mi= 0.0252 no. of moles= 0.18 0.025= 0.0025 GHANT HBr - It, NH BY weak base strongacid salt Ilo.0025 0.0025 Lo -0.0025 -0.0025 to-0025 0.0025 Total volume = 0.025+ 0.025= 0.052 [<<H, NH B373 > 0.0025 = 0.05M {} 0-05 for this type of salt plt formula: I pkwaly) ، وما - ام - دماامد - ام pit- + [14-8-77 – log co-os)] = 3.266

(E) HBr Molarity = OIM volume = 31m1= 0.0312 no-of moles a 0-031X0-1=0.0031 G-Hant HBr H, NHBY I 0.0025 0.003) el-0.0025-0-0025 E o oooooo Total volume = 0.025 + 0.03 0.050 SHBAJ>£H+] > 9-0008 - = 0.01071 0.056 - pits log 314+] = -109 (0.01071) - 1-97

(E) HBr Molarity = OIM volume = 31m1= 0.0312 no-of moles a 0-031X0-1=0.0031 G-Hant HBr H, NHBY I 0.0025 0.003) el-0.0025-0-0025 E o oooooo Total volume = 0.025 + 0.03 0.050 SHBAJ>£H+] > 9-0008 - = 0.01071 0.056 - pits log 314+] = -109 (0.01071) - 1-97

pH formula's for salt's weak acid + strong barse -salft ito pH = ± [pkw tpka + loge] strongacid & weakbase salf tito pH = ₃ [ pkW _pkke_loge]