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CAIE A-Level Chemistry 34.4.1 Acid–Base Properties of Amino Acids

Practise drawing amino-acid ionic forms at different pH values and interpreting the isoelectric point.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • draw a zwitterion with protonated –NH3+ and deprotonated –COO− groups but zero net charge
  • below the isoelectric point favour a net positive form; above it favour a net negative form
  • define isoelectric point as the pH at which the dominant amino-acid species has no overall charge

34.4.1—Acid / base properties of amino acids question 1

[Maximum number: 2]

Amino acids are molecules that contain −NH2-\mathrm{NH}_{2} and -COOH functional groups.
Glycine, H2NCH2COOH\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{COOH}, is the simplest stable amino acid.

Question (a)

(a)

The isoelectric point of glycine is 6.2.

[ 2 ]

Question (i)

(i)

Define isoelectric point.

[ 1 ]

Question (ii)

(ii)

Draw the structure of glycine at pH 4 .

[ 1 ]
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