Potassium thiocyanate

Structural formula
General
Surname	Potassium thiocyanate
other names	Potassium rhodanide
Molecular formula	KSCN
Brief description	Liquid, hygroscopic crystals
External identifiers / databases
CAS number 333-20-0 EC number 206-370-1 ECHA InfoCard 100.005.792 PubChem 516872 Wikidata Q412113
properties
Molar mass	97.18 g mol −1
Physical state	firmly
density	1.89 g cm −3
Melting point	175 ° C
boiling point	Decomposition: 500 ° C
Vapor pressure	<1 h Pa (20 ° C)
solubility	very good in water (2170 g l −1 at 20 ° C) good in DMSO (200 g l −1 at 25 ° C)
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 302 + 312 + 332-412 EUH: 032 P: 273-302 + 352
Toxicological data	854 mg kg −1 ( LD 50 ,  rat ,  oral )
Thermodynamic properties
ΔH f 0	−200.2 kJ / mol
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Potassium thiocyanate (KSCN, also: Kaliumrhodanid ) is a salt of thiocyanic acid ( thiocyanate acid).

properties

At room temperature, potassium thiocyanate consists of crystals that slowly dissolve in air . It dissolves very well in water, whereby the solution cools down considerably. The melting temperature is about 175 ° C. The crystals are readily soluble in ethanol and acetone .

Manufacturing

Potassium thiocyanate can be produced by melting together potassium cyanide and sulfur or from potassium hydroxide and ammonium thiocyanate . The latter is obtained from carbon disulfide and ammonia under pressure and elevated temperature:

${\displaystyle \mathrm {CS_{2}+2\ NH_{3}\longrightarrow NH_{4}SCN+H_{2}S} }$

use

Potassium thiocyanate serves as a detection agent for Fe ³⁺ ions present in aqueous solutions . The detection reaction is based on the formation of iron (III) thiocyanate , Fe (SCN) ₃ , which is blood red in aqueous solution:

${\displaystyle \mathrm {Fe^{3+}+3\ SCN^{-}+3\ H_{2}O\longrightarrow [Fe(SCN)_{3}(H_{2}O)_{3}]} }$

Iron (III) ions and thiocyanate ions react in an aqueous environment to form the blood-red iron (III) complex.

Potassium thiocyanate can also serve as a detection reagent for copper (II) ions. To do this, copper (II) ions are reduced to copper (I ) ions with sodium sulfite solution, which form a colorless precipitate with thiocyanate:

${\displaystyle \mathrm {2\ Cu^{2+}+\ SO_{3}^{2-}+3\ H_{2}O\longrightarrow SO_{4}^{2-}+2\ H_{3}O^{+}\ +2\ Cu^{+}} }$

${\displaystyle \mathrm {Cu^{+}+\ SCN^{-}\longrightarrow CuSCN_{(s)}} }$

The copper (I) thiocyanate can be seen as a colorless precipitate

Cobalt (II) thiocyanate from cobalt (II) chloride and potassium thiocyanate (above in acetone, below in water)

Cobalt (II) ions can also be detected with potassium thiocyanate. This creates red-violet cobalt (II) thiocyanate in water , which turns blue when alcohol or acetone is added.

${\displaystyle \mathrm {Co^{2+}+2\ SCN^{-}\longrightarrow Co(SCN)_{2}} }$

In addition, the chloride content of a nitric acid solution can be determined using a standard potassium thiocyanate solution using the Volhard method. This is a back titration. In the first step, the chloride ions are precipitated as silver chloride with a defined excess of silver nitrate . In the second step, the excess silver ions are then titrated against potassium thiocyanate. Fe ³⁺ ions are used as an indicator :

${\displaystyle \mathrm {Cl^{-}+Ag^{+}\longrightarrow AgCl\downarrow } }$

${\displaystyle \mathrm {Ag^{+}+SCN^{-}\longrightarrow AgSCN\downarrow } }$

${\displaystyle \mathrm {Fe^{3+}+3\ SCN^{-}\longrightarrow Fe(SCN)_{3}} }$

The iron (III) thiocyanate forms octahedral complexes in aqueous solution, which color the solution deep red.

Other uses are the production of cold mixtures, pesticides, plastics and metal stains. It is also used in analog photography to tone pictures.

Individual evidence

1. ↑ Entry on potassium thiocyanate. In: Römpp Online . Georg Thieme Verlag, accessed on July 7, 2014.
2. ↑ ^{a b c d e f} Entry on potassium thiocyanate in the GESTIS substance database of the IFA , accessed on January 9, 2019(JavaScript required) .
3. ↑ ^{a b} Data sheet potassium thiocyanate (PDF) from Merck , accessed on January 18, 2011.
4. ↑ Dimethyl Sulfoxide (DMSO) Solubility Data. Gaylord Chemical Company, LLC; Bulletin 102, June 2014, p. 14. (PDF)
5. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-20.
6. ^ ^{A b} A. F. Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 .
7. ↑ Heinrich Remy : Textbook of Inorganic Chemistry. Volume II, Akademische Verlagsgesellschaft Geest & Portig, Leipzig 1961, p. 356.
8. ↑ Reinhard Matissek, Gabriele Steiner, Markus Fischer: Food analysis . 5th edition. Springer Spectrum, Berlin / Heidelberg 2014, ISBN 978-3-642-34828-0 , p. 434 ff .