A) A solution is 17.3 mM in a weak acid and 86.5 mM in itssodium salt. The pH of

Question

A) A solution is 17.3 mM in a weak acid and 86.5 mM in itssodium salt. The pH of the solution is 6.5. What is thepKa of the weak acid? B)In what pH range would you expect each of the followingmolecules to have an average net charge close to zero? Note: High-precision answers are not asked for here, so donot carry out full explicit calculations for simultaneousequilibrium of all the ionizable groups. Instead, begin byindicating which ionization states of the molecule you expectshould be present as the major species, when the average net chargeis zero. Then, estimate the value of pH that should ensurethe needed distribution of ionization states. Give yourestimate as the nearest whole-number value, or pair of whole-numbervalues if you're on the fence. i.glycine ii. phenylalanine iii.tyrosine iv.arginine v.histidine vi.the dipeptide Glu-Ala vii.The dipeptide Glu-Lys A) A solution is 17.3 mM in a weak acid and 86.5 mM in itssodium salt. The pH of the solution is 6.5. What is thepKa of the weak acid? B)In what pH range would you expect each of the followingmolecules to have an average net charge close to zero? Note: High-precision answers are not asked for here, so donot carry out full explicit calculations for simultaneousequilibrium of all the ionizable groups. Instead, begin byindicating which ionization states of the molecule you expectshould be present as the major species, when the average net chargeis zero. Then, estimate the value of pH that should ensurethe needed distribution of ionization states. Give yourestimate as the nearest whole-number value, or pair of whole-numbervalues if you're on the fence. i.glycine ii. phenylalanine iii.tyrosine iv.arginine v.histidine vi.the dipeptide Glu-Ala vii.The dipeptide Glu-Lys

Explanation / Answer

(B) pI of Gly = 5.75 ˜ 6 pI of Phe = 5.75 ˜ 6 pI Tyr = (9.5+10)/2 = 9.75 ˜ 10 pI Arg = (9.5+12.5)/2 = 11 pI His = (6+9.5)/2 = 7.75 ˜8

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