Cobalt(II) hydroxide Chemical Properties

Melting point:

°Cd ec.)

Density 

3.597 g/mL at 25 °C(lit.)

vapor pressure 

0Pa at 20℃

storage temp. 

Inert atmosphere,Room Temperature

solubility 

slightly soluble in H2O; soluble in acid solutions

form 

Powder

Specific Gravity

3.597

color 

Pink to purple

PH

9.15(1 mM solution);9.15(10 mM solution);9.15(100 mM solution)

Water Solubility 

Soluble in acids and ammonia. Very slightly soluble in water. Insoluble in dilute alkalis.

Sensitive 

Air Sensitive

Merck 

14,2442

Solubility Product Constant (Ksp)

pKsp: 14.23

Exposure limits

ACGIH: TWA 0.02 mg/m3

Stability:

Stability

CAS DataBase Reference

21041-93-0(CAS DataBase Reference)

EPA Substance Registry System

Cobalt hydroxide (Co(OH)2) (21041-93-0)

Safety Information

Hazard Codes 

Xn,N

Risk Statements 

20/21/22-36/37/38-50/53-42/43-40-20/22

Safety Statements 

26-37/39-36

RIDADR 

UN 3077 9 / PGIII

WGK Germany 

3

RTECS 

GG0904500

TSCA 

Yes

MSDS

• Language:English Provider:Cobalt hydroxide
• Language:English Provider:SigmaAldrich
• Language:English Provider:ALFA

Cobalt(II) hydroxide Usage And Synthesis

Physical Properties

Two forms occur, a rose-red powder (more stable) and a bluish-green powder less stable than the red form; rhombohedral crystals; density 3.597 g/cm3; decomposes on heating; practically insoluble in water 3.2 mg/L; Ksp 1.0x10–15; soluble in acids and ammonia; insoluble in dilute alkalis.

The addition of alkali metal hydroxides to solutions of cobalt(II) salts results in the precipitation of cobalt(II) hydroxide in either a blue or pink form depending upon the conditions. The pink form is the more stable of the two and is obtained when a suspension of the blue form is allowed to stand or is warmed. Cobalt(II) hydroxide is amphoteric, dissolving in alkalis to form blue solutions of the [Co(OH)4]2~ ions. In the presence of alkali, suspensions of Co(OH)8 are oxidized by air to the brown CoO(OH), this oxidation being brought about rapidly by oxidants such as hypochlorite, bromine water or hydrogen peroxide. The pink Co(OH)2 (density 3.597) has the brucite (Mg(OH)2) structure in which the cobalt atoms are surrounded by six hydroxides. The blue form is more disordered, but its structure is not known for certain.

Uses

Cobalt(II) hydroxide is used as a drier for paints and varnishes and is added to lithographic printing inks to enhance their drying properties. Other applications are in the preparation of cobalt salts; as a catalyst; and in storage battery electrodes.

Preparation

Cobalt(II) hydroxide is obtained as a precipitate when an alkaline hydroxide is added to an aqueous solution of cobalt(II) salt:
CoCl2 + 2NaOH → Co(OH)2 + 2NaCl
Co(NO3)2 + 2NaOH → Co(OH)2 + 2NaNO3

Reactions

Thermal decomposition to cobaltous oxide, CoO, occurs at 168°C in a vacuum.
Cobalt(II) hydroxide is oxidized by air and other oxidizing agents, forming cobalt(III) hydroxide, Co(OH)3. Reactions with mineral acids produce corresponding Co²⁺ salts.

Description

The addition of alkali metal hydroxides to solutions of cobalt(II) salts results in the precipitation of cobalt(II) hydroxide in either a blue or pink form depending upon the conditions. The pink form is the more stable of the two and is obtained when a suspension of the blue form is allowed to stand or is warmed. Cobalt(II) hydroxide is amphoteric, dissolving in alkalis to form blue solutions of the [Co(OH)4]2- ions. In the presence of alkali, suspensions of Co(OH) are oxidized by air to the brown CoO(OH), this oxidation being brought about rapidly by oxidants such as hypochlorite, bromine water or hydrogen peroxide. The pink Co(OH)2 (density 3.597) has the brucite (Mg(OH)2) structure in which the cobalt atoms are surrounded by six hydroxides. The blue form is more disordered, but its structure is not known for certain.

Chemical Properties

Rose-red powder.Soluble in acids and ammonium salt solutions; insoluble in water and alkalies.

Uses

Cobalt salts, paint and varnish driers, catalyst, storage-battery electrodes.

Uses

Cobalt(II) hydroxide is used as a drying agent for paints and varnishes. It acts as an aid to dry the lithographic inks and catalyst in the preparation of battery electrode impregnating solutions. It is also involved in the synthesis of other cobalt compounds.

Flammability and Explosibility

Not classified

Cobalt(II) hydroxide(21041-93-0)Related Product Information

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