Question

1. The pKa's of the amino acid methionine are 2.28 and 9.21. The zwitterion of methionine is given below (1). S Н,с NH3 (a) Explain why structure (I) is an intermediate ion. Write balanced chemical reactions to support your reasoning (b) Draw the conjugate acid AND conjugate base form of the amino acid shown above (c) A 15-mL aliquot solution consisted 0.25M of the zwitterion of methionine and 0.30M of its conjugate acid was titrated with 0.15M NaOH, calculate the equilibrium pH after the addition of 15mL and 65mL of N2OH NOTE: The 15-mL sample contains both 0.25M of the zwitterion of methionine and 0.30M of its conjugate acid of methionine. In other words, the sample total volume is only 15mL NOT 30mL

Answer 1

An Se - Given ha The pka's of he amino acid methionine 2.8 and .aj. are aliguo Soluhon Considen A1S-me 0 SM Zpidteion d methionine S o.30 M Conjugald atid red o.IS M Nao E). addihon o and 65ML on because the strueure s an inferme diade in NH Porm basic Exists dmine as a the acidic Cay bozylie aceapts pre ton and base acid coo fom greup Exists an acid donode Pro fen AI 142 NH COOH Cn be dvacon -f/ lows The Consegadeacid Cook CH - (,) dracon a The conjugte oase Can be

-Cpo - CH CcooR pka of Car bexy temna od NaoH - (i5 xo-25 +I5yo-15 The esuting C 2uisie on f(t5+13)m (sx0.3-15X The e ti onjugade acd Ci5415 O. O7S M Hassel bulch ezuahon Hend son nding the pH pkaLegC Cenjugote acid L Co-t fo.075) 6s mL o Nao PKa amin e esmina (NHJa 9.2 The esuting congugate base] E 6syo s-(I5x0-25+ mL0.ol875 M y oualus

(3) he xeating O.ofu37Sm mmo Henlen son Hasselbulch ewation Acrding do the Cwie ion pha e Canjugte base pH 92Log Lo01F75/o. 0s4395)f. 5e