Aspartic acid has pK_a values 2.0 (alpha-COOH), 3.9 (side-chain COOH) and 10.0 (NH3+). Taking pI as the mean of the pKa values flanking the neutral species, which statements are correct?

At pH 7 it migrates towards the anode.

At pH 12 the predominant species has net charge -2.

At pH 2.0 it migrates towards the anode.

At pH 7 it migrates towards the anode.

At pH 12 the predominant species has net charge -2.

JEE Advanced levelOne or more correct optionsDifficulty 3 of 3bm081

Aspartic acid has $p K_{a}$ values 2.0 (alpha-COOH), 3.9 (side-chain COOH) and 10.0 ( $NH X_{3} X^{+}$ ). Taking pI as the mean of the pKa values flanking the neutral species, which statements are correct?

pI =

(2.0 + 3.9) /2 = 2.95

. At pH 7 (above pI) it is

- 1

and goes to the anode. At pH 12 both carboxyls are ionised and the amino group is free, net

- 2

. At pH 2.0 (below the pI) the net charge is positive (about

+ 0.5

), so it goes to the cathode and the last statement is false.