Synthetic Inorganic Chemistry

218 ELEMENTS OF GROUP III

precipitate remains unaffected, but after the NH4OH is all

neutralized (shown by the solution ceasing to smell of am-

monia after shaking) a little more acetic acid redissolves the

precipitate.

Ammonium hydroxide and acetic acid are of equal strength as

base and acid respectively. That the A1(OH) 3 does not dissolve

in excess NH4OH indicates that it is not a strong enough acid to

react with a base of this feeble strength. That it does dissolve

in acetic acid indicates that it is a strong enough base to react with

an acid of the feeble strength of acetic acid. Thus aluminum

hydroxide, although an extremely weak base, is more basic than

acidic.

6. Instability of Aluminum Carbonate. Add together
   solutions of A1 2 (SO4) 3 and Na 2 CO 3. Effervescence takes
   place, and the escaping gas can be shown to be carbon dioxide.
   A gelatinous white precipitate is formed resembling previous
   precipitates of A1(OH) 3. To show whether this precipitate
   is really the hydroxide, or perhaps the carbonate or basic
   carbonate, collect some of it on a filter and wash it very
   thoroughly with water to remove any excess of Na 2 CO 3.
   Then add an acid (say HC1) to the precipitate and observe
   that it dissolves without a trace of effervescence.

Reference books tell us that aluminum carbonate has never
been prepared. In this experiment we brought together the ions
of aluminum carbonate and the result showed that this salt cannot
exist in solution. The reaction might be described as the hydroly-
sis of aluminum carbonate:
2A1+++ 3CO 3 ~~
6H 2 O^=;6OH" 6H+
I 1
2A1(OH) 3 3H 2 CO 3
1 I
2A1(OH) 3 i 3H 2 O + 3CO 21
That aluminum carbonate is thus completely hydrolyzed indicates
that the base and the acid are both very weak.