Potassium dicyanidoaurate (I)

Structural formula
General
Surname	Potassium dicyanidoaurate (I)
other names	Gold potassium cyanide Potassium cyanoaurate (I) Potassium gold cyanide
Molecular formula	K [Au (CN) 2 ]
Brief description	colorless, odorless solid
External identifiers / databases
CAS number 13967-50-5 EC number 237-748-4 ECHA InfoCard 100.034.303 PubChem 159710 ChemSpider 140427 Wikidata Q1341604
properties
Molar mass	288.10 g mol −1
Physical state	firmly
density	3.45 g cm −3
solubility	soluble in water
safety instructions
GHS hazard labeling from  Regulation (EC) No. 1272/2008 (CLP) , expanded if necessary danger H and P phrases H: 290-300-330-315-317-318-410 EUH: 032 P: 260-301 + 310-305 + 351 + 338-320-361-405-501
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Kaliumdicyanidoaurat (I) , K [Au (CN) ₂ ], is a potassium - salt of the complex Dicyanidoaurat (I) - anions [Au (CN) ₂ ] ^- . The gold content of the salt is around 68.2%. The complex is 100 times more stable than yellow blood liquor salt .

${\displaystyle \mathrm {Au^{+}+2\ CN^{-}\rightleftharpoons [Au(CN)_{2}]^{-}} \quad \quad K_{A}=\mathrm {\frac {[[Au(CN)_{2}]^{-}]}{[Au^{+}]\cdot [CN^{-}]^{2}}} =1,0E+37}$

As a result of this complexation, the gold ion concentration in water drops so extremely that it reduces the normal potential of gold (+1.69 volts) to the potential of a base metal (+0.20 volts). Therefore, in cyanide leaching, elemental gold is oxidized with atmospheric oxygen.

Cyanide leaching

When gold is extracted ( cyanide leaching ), solutions of potassium dicyanidoaurate (I) are formed:

${\displaystyle \mathrm {4\ Au\ +\ 8\ KCN\ +\ O_{2}\ +\ 2\ H_{2}O\ \longrightarrow } }$ ${\displaystyle \mathrm {\ 4\ K[Au(CN)_{2}]\ +\ 4\ KOH} }$

To isolate the gold in elemental form, this complex is then reduced with zinc (Zn):

${\displaystyle \mathrm {2\ K[Au(CN)_{2}]\ +\ Zn\ \longrightarrow } }$ ${\displaystyle \mathrm {\ K_{2}[Zn(CN)_{4}]\ +\ 2\ Au} }$

use

The connection is used in electroplating for gold-plating conductive materials. During electrolysis , these are switched as a minus pole. In this cathode region, the [Au (CN) are ₂ ] ^- - anion is reduced to a thin layer of gold.

Individual evidence

1. ↑ ^{a b c} Entry on potassium dicyanoaurate (I) in the GESTIS substance database of the IFA , accessed on January 8, 2018(JavaScript required) .
2. ↑ ^{a b} data sheet potassium gold cyanide from AlfaAesar, accessed on January 22, 2018 ( PDF )(JavaScript required) .
3. ↑ Not explicitly listed in Regulation (EC) No. 1272/2008 (CLP) , but with the indicated labeling it falls under the group entry salts of hydrogen cyanide with the exception of complex cyanides such as ferrocyanides, ferricyanides and mercuric oxycyanide and those specified elsewhere in this Annex in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
4. ↑ chemieunterricht.de: Applications of complexation , see also Nernst equation
5. ^ AG Gray, HW Dettner: Modern galvanic metal deposition , Carl Hanser, Munich. doi : 10.1002 / bbpc.19590630528 .