Note 380 — Chapter X · ALUMINIUM; AMPHOTERIC HYDROXIDES; HYDROLYSIS OF SALTS. THE ALUMINIUM AND ZINC GROUPS

Amphoteric substances of a different class are also known, which have, at the same time, moderately

strong

acid and moderately

strong

basic functions. Glycocoll, H

2

N.CH

2

COOH, a derivative of acetic acid and ammonia, contains an acid group, the —COOH group, the hydrogen of which is approximately as ionizable as the hydrogen in the corresponding group in acetic acid, CH

3

COOH. The ammonia residue, H

2

N—, in glycocoll, forms with water a hydroxide, corresponding to ammonium hydroxide, which likewise is approximately as ionizable as is ammonium hydroxide. In the hydroxide of glycocoll we have, consequently, both a moderately strong acid, and a moderately strong basic, group. In this, and in similar cases,

salt formation between the acid and the basic groups of the amphoters takes place to as great an extent as if the functions were attributes of distinct compounds

. Glycocoll in aqueous solution is present, then, chiefly in the form of a salt, for instance,

H₃ N .CH₂.CO O

└ ─────── ┘

, corresponding to ammonium acetate, CH

3

COONH

4

. For an elaborate discussion of the equilibrium conditions in solutions of amphoteric compounds

vide

Walker,

Z. phys. Chem.

,

49

and

51

.