Question

please answer both 12 and 13! and explain, thank you!!

12). (4 pts) Lactic acid builds up in has a pH of 1.9. What is the K, for the a In our muscles after a workout. A solution of 0.2 M lactic acid OR •X A 1.oxloly A) 0.187 B) 0.013 C) 8.5 x 10" D) 3.2 x 10 E) 1.6 x 10" 14 POH 13. ( 4 pts) Caffeine, a stimulant in coffee and tea, is a weak base that tin coffee and tea, is a weak base that ionizes in water according solution of caffeine has a pH of 8.45. What is the Kb of caffeine. CgH10N4O2(aq) + H200) = HC H1N. (aq) + OH(aq) A) 8.4 x 10-17 B) 5.3 x 10-11 C) 1.6 x 10 D) 0.013 E) 0.187

Answer 1

12)

use:
pH = -log [H+]
1.9 = -log [H+]
[H+] = 1.259*10^-2 M
HA dissociates as:

HA          ----->     H+   + A-
0.2                 0         0
0.2-x               x         x


Ka = [H+][A-]/[HA]
Ka = x*x/(c-x)
Ka = 1.259*10^-2*1.259*10^-2/(0.2-1.259*10^-2)
Ka = 8.5*10^-4
Answer: C

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