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JEE Main levelOne or more correct optionsDifficulty 2 of 3bm072

Alanine has $p K_{a 1} = 2.3$ (COOH) and $p K_{a 2} = 9.7$ ( $NH X_{3} X^{+}$ ); its pI is 6.0. Which statements are correct?

AAt pH 6.0 the predominant species is the zwitterion.
BAt pH 12 the predominant species has zero net charge.
CAt pH 12 alanine moves towards the anode.
DAt pH 1.0 the predominant species has net charge $+ 1$ .

Answer: A, C, D

At pH 1 (below 2.3) the species is

H X_{3} N X^{+} - CH (CH X_{3}) - COOH

, net

+ 1

. At pH 6.0 (between the two pKa values) the zwitterion predominates. At pH 12 (above 9.7) it is

H X_{2} N - CH (CH X_{3}) - COO X^{-}

with net charge

- 1

, so it goes to the anode; hence the zero-charge statement is false.

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