Cadmium hydroxide

Cadmium hydroxide is an inorganic compound with the formula Cd(OH)2. It is a white crystalline ionic compound that is a key component of NiCd batteries.[3]

Cadmium hydroxide
Names
IUPAC name
Cadmium(II) hydroxide
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.040.137
UNII
Properties
Cd(OH)2
Molar mass 146.43 g/mol
Appearance white crystals
Density 4.79 g/cm3
Melting point 130 °C (266 °F; 403 K)
Boiling point 300 °C (572 °F; 573 K) (decomposes)
0.026 g/100 mL
Solubility soluble in dilute acids
-41.0·10−6 cm3/mol
Structure
hexagonal
Thermochemistry
96 J·mol−1·K−1[1]
−561 kJ·mol−1[1]
Hazards
NIOSH (US health exposure limits):
PEL (Permissible)
 [1910.1027] TWA 0.005 mg/m3 (as Cd)[2]
REL (Recommended)
 Ca[2]
IDLH (Immediate danger)
 Ca [9 mg/m3 (as Cd)][2]
Related compounds
Other anions
 Cadmium chloride,
Cadmium iodide
Other cations
 Zinc hydroxide,
Calcium hydroxide,
Magnesium hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Structure, preparation, and reactions

Cadmium hydroxide adopts the same structure as Mg(OH)2, consisting of slabs of octahedral metal centers surrounded by octahedral of hydroxide ligands.[4]

It is produced by treating cadmium nitrate with sodium hydroxide:

Cd(NO3)2 + 2 NaOH → Cd(OH)2 + 2 NaNO3

Attempted preparation from other cadmium salts is more complicated.[3]


Cd(OH)2 and cadmium oxide react equivalently. Cadmium hydroxide is more basic than zinc hydroxide. It forms the anionic complex Cd(OH)42− when treated with concentrated caustic soda solution. It forms complexes with cyanide, thiocyanate and ammonium ions when added to the solutions of these ions. Cadmium hydroxide loses water on heating, producing cadmium oxide. Decomposition commences at 130 °C and is complete at 300 °C. Reactions with mineral acids (HX) produce the corresponding cadmium salts (CdX2). With hydrochloric acid, sulfuric acid and nitric acid, the products are cadmium chloride, cadmium sulfate and cadmium nitrate, respectively.

Uses

It is generated in storage battery anodes, in nickel-cadmium and silver-cadmium storage batteries in its discharge:

2 NiO(OH) + 2 H2O + Cd → Cd(OH)2 + Ni(OH)2

References
  1. Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A21. ISBN 0-618-94690-X.
  2. NIOSH Pocket Guide to Chemical Hazards. "#0087". National Institute for Occupational Safety and Health (NIOSH).
  3. Karl-Heinz Schulte-Schrepping, Magnus Piscator "Cadmium and Cadmium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, 2007 Wiley-VCH, Weinheim. doi:10.1002/14356007.a04_499.
  4. Hemmingsen, L.; Bauer, R.; Bjerrum, M. J.; Schwarz, K.; Blaha, P.; Andersen, P., "Structure, Chemical Bonding, and Nuclear Quadrupole Interactions of β-Cd(OH)2:  Experiment and First Principles Calculations", Inorganic Chemistry 1999, volume 38, 2860-2867. doi:10.1021/ic990018e
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