Beryllium Hydroxide, Be(OH)₂

Beryllium Hydroxide, Be(OH)₂, is precipitated as a white gelatinous precipitate from dissolved beryllium salts by ammonia, ammonium sulphide, or caustic alkalies. It dissolves in ammonium carbonate or excess of alkali solution, and separates from any of these solutions on boiling. Vauquelin first observed, during an examination of the emerald, that the earth deposited from a boiling potassium hydroxide solution was not alumina. The similarities between the hydroxides of aluminium and beryllium had prevented their distinction, and still make it difficult to identify, isolate, or estimate beryllia. Vauquelin noted a number of differences between beryllia and alumina, and realised that the former was more basic. The properties established for beryllium and its compounds indicate quite clearly that it is more basic than aluminium and less basic than magnesium. Beryllium hydroxide is amphoteric; its acid properties are slightly stronger than those of zinc, but are very weak.

The carbonates of the alkalies precipitate a product containing some carbon dioxide. Boiling expels the carbon dioxide, but the precipitate usually occludes about 2 per cent, of alkali. Beryllium hydroxide dissolves readily in dilute acids and caustic alkalies, slowly in concentrated solutions of sodium bicarbonate or ammonium carbonate, and immediately in a saturated, boiling solution of the bicarbonate. Dilution precipitates it from its solution in alkalies - slowly in the cold, rapidly at 100° C. When washed with cold water it goes slowly into colloidal solution; washing with ammonium acetate solution prevents this.

Beryllium hydroxide is more reactive when freshly precipitated than after standing or heating in contact with water, and it seems to lose its colloidal character rapidly after being precipitated. Three forms of beryllium hydroxide have been described; and when precipitated from boiling dilute alkali hydroxide solutions it is granular, perhaps crystalline, and not adsorbent.

The following heats of reaction of the hydroxide with dilute acids have been obtained: -

[Be(OH)₂]+SO₄.Aq. = BeSO₄.Aq. + 161 Cal.
[Be(OH)₂]+2HCl.Aq. = BeCl₂.Aq.+ 13.64 Cal.
[Be(OH)₂]+2HF.Aq. = BeF₂.Aq. +19.683 Cal.