Tetraammine copper sulfate

Structural formula
General
Surname	Tetraammine copper sulfate
other names	Tetrammine copper (II) sulfate
Molecular formula	[Cu (NH 3 ) 4 ] SO 4 • H 2 O
External identifiers / databases
CAS number 10380-29-7 EC number 626-953-8 ECHA InfoCard 100.155.305 PubChem 61513 ChemSpider 55433 Wikidata Q413075
properties
Molar mass	245.75 g mol −1
Physical state	firmly
density	1.81 g cm −3
safety instructions
GHS labeling of hazardous substances Monohydrate Caution H and P phrases H: 315-319-335 P: 261-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Tetraammine copper (II) sulfate [Cu (NH ₃ ) ₄ ] SO ₄ , (former names: Cuprum sulfuricum ammoniatum , sulfuric acid copper oxide ammonia, copper almia, cupric ammonium sulfate, tetrammine copper (II) sulfate) is a complex salt of divalent copper and sulfuric acid . As a solid, it is present as a monohydrate [Cu (NH ₃ ) ₄ ] SO ₄  · H ₂ O. The deep blue color of the salt crystals is caused by the tetraammine complex [Cu (NH ₃ ) ₄ ] ²⁺ of copper, which is complexed by two additional water molecules in aqueous solution. The salt, which slowly weathered in air to a green powder, has a decomposition point of approx. 150 ° C.

Tetraammine copper (II) sulfate is formed by adding an aqueous copper (II) sulfate solution with excess ammonia water:

${\displaystyle \mathrm {CuSO_{4}+4\ NH_{3}+H_{2}O\longrightarrow \ {[Cu(NH_{3})}_{4}]SO_{4}\cdot \ H_{2}O} }$

Tetraammine copper (II) sulfate monohydrate [Cu (NH ₃ ) ₄ ] SO ₄ · H ₂ O

The color change from pale blue to deep blue can be used to detect the copper ions. The use of copper salts as a secret ink is based on the formation of the tetraammine copper complex .

Although the tetraammine copper (II) salts are stable complex salts, a reaction with hydrogen sulfide (H ₂ S) is possible: When adding hydrogen sulfide (H ₂ S), black copper (II) sulfide is precipitated. The copper (II) ion concentration resulting from the equilibrium of the complex according to the equation

${\displaystyle \mathrm {[Cu(NH_{3})_{4}]^{\,2+}\rightleftharpoons \ Cu^{\,2+}+4\ NH_{3}} }$

is higher than the max. Solution concentration of the copper (II) sulfide . Therefore, despite the complex compound, copper (II) sulfide is precipitated.

When milk of lime is added to a solution of tetraammine copper (II) sulfate, a blue-green precipitate forms. This color pigment, also known as lime blue or new blue , is used for painters' paints.

Tetraammine copper sulfate was first synthesized in 1644 by Johan Baptista van Helmont .

The aqueous solution was introduced as "volatile copper oxide tincture" (Tinctura veneris volatilis) by Herman Boerhaave (1668–1738), but was no longer used.

Individual evidence

1. ↑ ^{a b c} Datasheet Tetraamminecopper (II) sulfate monohydrate from Sigma-Aldrich , accessed on April 24, 2011 ( PDF ).
2. ↑ Jander-Wendt: Textbook of analytical and preparative inorganic chemistry , 3rd edition, S. Hirzel Verlag, Sttg., 1959, p. 243.
3. ↑ Brockhaus der Naturwissenschaften und der Technik , 4th edition, SFABrockhaus Verlag, Wiesbaden, 1958, p. 325.