Question

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4. Suppose Compound B is the conjugate base of Compound A. Calculate the approximate concentration of Compound A that must be present in a 0.042 M solution of Compound B to produce a pH of 4.96. The K. for Compound A is 1.8 x 109. Show your work. Round your final answer to the nearest hundredth decimal place. (5pts) 5. Consider the structure below. Then using the empty boxes, answer parts (a)-(e). HO (a) (1 pts) Draw a constitutional isomer expected to have approximately the same pka as the compound above. (b) (2pts) Draw a constitutional isomer that you expect to be less acidic than the compound above. (e) (2pts) Draw a constitutional isomer that is roughly 10 times more acidic than the compound above. (a) (b) (c) 6. The relative acidity (or basicity) of compounds is influenced by factors including: periodic trends, resonance, induction, and orbitals. For each case below there are two protons circled. Indicate which one is most acidic and briefly explain the factor that is most responsible. If resonance is the determining factor, draw relevant resonance structures to clearly illustrate. (Ipt each correct answer, 2pt for each valid explanation) (b) (a) (d) (c)

Answer 1

compound B is conjugate base Compound A 80 pH of sol = 4.96 Compound A Compound B weak acid conjugate base 0.042M kaf compound A= 1.8810-5 bra = -log(ka) E-log (1.8818-5) since Solution contain compound A and its conjugate base compound B Solution is buHer Solution and pH can be calculated using Hendersons Hasselbach equation pH = pka + log [conjugate base] [ wear acid] 4.74 weak aud 0.22 4.96 = 4.74 + log [compound B] [ compound a log [compound B] [compounda] antilog 10-22) [compound B] [compound A 1.66 [compound B] [compound A) (0.042) compound A [compound n = 0.025M concentration of Lcompound A) 0.025M 1.66 -