Cadmium hydroxide
{{chembox
| Watchedfields = changed
| verifiedrevid = 400824446
| Name = Cadmium hydroxide
| ImageFile1 = Cd(OH)2.png
| ImageFile2 = Mg(OH)2Xray.jpg
| ImageName1 = Cadmium hydroxide structure
| IUPACName = Cadmium(II) hydroxide
| OtherNames =
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 8488675
| PubChem = 10313210
| InChI = 1/Cd.2H2O/h;2*1H2/q+2;;/p-2
| SMILES = [Cd+2].[OH-].[OH-]
| InChIKey = PLLZRTNVEXYBNA-NUQVWONBAA
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/Cd.2H2O/h;2*1H2/q+2;;/p-2
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = PLLZRTNVEXYBNA-UHFFFAOYSA-L
| CASNo = 21041-95-2
| CASNo_Ref = {{cascite|correct|CAS}}
| CASNoOther =
| UNII_Ref = {{fdacite|correct|FDA}}
| UNII = 6Y413R87BT
| RTECS =
}}
|Section2={{Chembox Properties
| Formula = Cd(OH)2
| MolarMass = 146.43 g/mol
| Appearance = white crystals
| Density = 4.79 g/cm3
| Solubility = 0.026 g/100 mL
| SolubleOther = soluble in dilute acids
| SolubilityProduct = 7.2{{e|−15}} {{cite book |author1=John Rumble |title=CRC Handbook of Chemistry and Physics |date=June 18, 2018 |publisher=CRC Press |isbn=978-1138561632 |pages=5–188|edition=99 |language=English}}
| pKa = 10{{cite book|title=Ionisation Constants of Inorganic Acids and Bases in Aqueous Solution|editor-first=D. D.|editor-last=Perrin|edition=2nd|series=IUPAC Chemical Data|issue=29|publisher=Pergamon|location=Oxford|year=1982|publication-date=1984|orig-date=1969|lccn=82-16524|isbn=0-08-029214-3|at=Entry 22}}
| MeltingPtC = 130
| MeltingPt_notes =
| BoilingPtC = 300
| BoilingPt_notes = (decomposes)
| MagSus = −41.0·10−6 cm3/mol
}}
|Section3={{Chembox Structure
| Coordination =
| CrystalStruct = hexagonal
}}
|Section4={{Chembox Thermochemistry
| DeltaHf = −561 kJ·mol−1{{cite book| author = Zumdahl, Steven S.|title =Chemical Principles 6th Ed.| publisher = Houghton Mifflin Company| year = 2009| isbn = 978-0-618-94690-7|page=A21}}
}}
|Section7={{Chembox Hazards
| ExternalSDS =
| REL = Ca{{PGCH|0087}}
| PEL = [1910.1027] TWA 0.005 mg/m3 (as Cd)
}}
|Section8={{Chembox Related
| OtherAnions = Cadmium chloride,
Cadmium iodide
| OtherCations = Zinc hydroxide,
Calcium hydroxide,
Magnesium 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 nickel–cadmium battery.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}}.
Structure
Cadmium hydroxide adopts the same structure as Mg(OH)2, consisting of slabs of metal centers, each bonded by six hydroxide ligands.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}} The Cd(OH)2 structure is a recurring motif in inorganic chemistry. For example it is adopted by vanadium ditelluride.{{cite journal |doi=10.1016/0022-4596(84)90120-8 |title=The Crystal Structure of Vanadium Ditelluride, V1+xTe2 |date=1984 |last1=Bronsema |first1=K.D. |last2=Bus |first2=G.W. |last3=Wiegers |first3=G.A. |journal=Journal of Solid State Chemistry |volume=53 |issue=3 |pages=415–421 }}
Preparation, and reactions
Cadmium hydroxide is produced by treating an aqueous solution containing Cd2+ (say cadmium nitrate) with sodium hydroxide:{{cite book|author1=F. Wagenknecht|author2=R. Juza|chapter=Cadmium hydroxide|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed. |editor=G. Brauer|publisher=Academic Press|year=1963|place=NY, NY|volume=2|pages=1096}}
: Cd(NO3)2 + 2 NaOH → Cd(OH)2 + 2 NaNO3
Cd(OH)2 and cadmium oxide exhibit similar reactions. Cadmium hydroxide is more basic than zinc hydroxide. It forms the anionic complex [Cd(OH)4]2− when treated with concentrated base. It forms complexes with cyanide, thiocyanate, and ammonia.
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) gives 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 + 2 Ni(OH)2