Question

5. The alcohol CH3CH,SH has an unusually small pKa of approximately 9.4 relative to ethanol, CH3CH2OH (pka - 16). a. Is CH CH SH more or less acidic than ethanol? (2 pts) b. Draw the conjugate base for each and explain the difference in acidity between CH3CH2SH and CH3CH2OH by analyzing the structures of the conjugate bases. (4 pts) c. Provide an arrow-pushing scheme for the reaction of one mole of CH3CH2SH with one mole of NaOH and provide the products of this reaction. (6 pts) 6. Consider the following equilibrium reaction: CH,COOH + HCO,s = pka = 4.19 = CH2COO- + H2CO, pk = 6.24 a. Calculate the equilibrium constant, Keg, for the acid-base reaction below: (5 pts) b. Describe which direction is favored in the equilibrium. Justify your answer (3 pts)

Answer 1

5a) CH CH SH pka - 9.4 CH₃CH₂OH pha - 16 CH, CH SH is more acidic than ethanol pha = -log Ka Kaz and dissociation constant , . A lower pla value means a strongeli acid, je, more dissociation - _ 9) Conjugata base of en_C_SK - CH CH, so conjugate base of CH₂ CH2OH CH CHLOG The negative charge on sin ch, chS is more stabilised than the negative Y urii

charge on 0 in CH₂ Choo. The more the stability of the conjugate base of after the acid ( here chcu SH and CH, CH₂OH) has lost a proton the more is the acidity of the acids. En CH₂ CHISH, s is less electronegative and easily gives off the Ht compared to en ch on where it is tightly bound to the highly electronegatuie o. c) CH CH - SH + NaOH - CH₂ CHS NaB+ Ho ar 84 - so Thiolate - +Ho anion 6) Cats coon + HCO3 = hs000 + H₂CO3 pka = 6.24. pka = 4.19 - keq = 10 (plap- plac) - Z10 (6-24 - 4119 .. (6.24-419) 7112.2018

Even without calculating the value of keq, it can be concluded that G H coon having a lower pha is more racidic and would easily give up its prolon and the equilibrium would lie to the right forward direction) From the keq value, as it is positive, the forward equilibrium is more favoured. (pha night acid - pka left acid Keq = 10 Co Hg 40 + H₂ Q CH 200M + HO iod HH
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