Ammonium sulfide group
The ammonium sulfide group [(NH 4 ) 2 S group] is a group of elements whose salts form sparingly soluble sulfides and hydroxides with a hydrogen sulfide solution in the presence of ammonia . The sulphides which precipitate in the acidic even at low sulphide concentrations were previously separated off as hydrogen sulphide groups .
In the filtrate of the hydrogen sulphide group, the following cations precipitate when ammonia water and ammonium sulphide solution are added (here indicated with the element symbols):
- Co and Ni (as CoS and NiS ),
- Mn , Zn and Fe (as MnS , ZnS and FeS ; the latter in the form of doubly and triply charged cations, although only iron (II) sulfide precipitates due to the reducing effect of sulfide) and
- Cr and Al (precipitate as hydroxides, since the element (III) sulfides would hydrolyze).
The sulphide precipitation in the basic range (ideally with ammonia / ammonium chloride buffer solution at pH values around 8 to 9) is used in the cation separation process for qualitative analysis (in inorganic chemistry ) for the separation and detection of heavy metal cations Co (II), Ni (II), Mn (II), Zn (II), Fe (II, III) as well as Al (III) and Cr (III). The filtrate is then the cations of ammonium - group and soluble group .
Group segregation
The precipitation of the ammonium sulfide group is followed by a separation of the cations from one another so that they can then be found undisturbed by means of detection reactions. You can alternatively subdivide this group further into urotropine and ammonium sulfide groups (in the narrower sense). For this purpose, the filtrate of the hydrogen sulfide group is first boiled with urotropine (= hexamethylenetetramine ) so that hydroxides precipitate (pH 5-6).
Urotropin group
The urotropin group includes:
- Fe 2 + / 3 + , detectable with red or yellow blood liquor salt (yellow blood liquor salt for Fe 3+ , red blood liquor salt for Fe 2+ ) as Prussian blue or with ammonium thiocyanate solution (Fe 3+ , oxidize Fe 2+ with H 2 O 2) ) as a red complex that can be shaken out in ether or amyl alcohol,
- Ti 2 + / 4 + , detectable as a yellow titanyl cation with hydrogen peroxide in acetic acid solution
- La 3+ ,
- Al 3+ , detectable as Thénards blue or as a fluorescent colored lacquer with Morin , as well
- Cr 3 + / 6 + , detectable by oxidation / conversion to yellow chromate .
Their hydroxides precipitate .
Ammonium sulfide group in the narrower sense
The ammonium sulfide group [(NH 4 ) 2 S] in the narrower sense then includes:
- Ni 2+ , detectable with dimethylglyoxime solution in ammonia as a raspberry-red complex [Ni (dmg) 2 ],
- Co 2+ , detectable as a complex with solid thiocyanate and pentanol or as a blue complex with [Hg (SCN) 4 ] 2− solution and
- Mn 2+ , detectable with lead (IV) oxide and nitric acid or sodium peroxodisulfate in acetic acid solution, which oxidize the manganese to violet permanganate ,
- Zn 2+ , detectable as white zinc sulfide or with cobalt nitrate as Rinmans green ,
- VO 4 3− , detectable with hydrogen peroxide in acid as reddish-brown peroxovanadium [V (O 2 )] 3+ or yellowish peroxovanadic acid H 3 [VO 2 (O 2 ) 2 ], as well
- W 3+ .
Web links
literature
- Michael Wächter: chemistry laboratory . Verlag Wiley-VCH, Weinheim 2011, p. 237ff, ISBN 978-3-527-32996-0
- Gerhart Jander: Introduction to the inorganic-chemical internship . S. Hirzel Verlag, Stuttgart 1990 (in 13th edition), ISBN 3-7776-0477-1
- Michael Wächter: Substances, particles, reactions . Verlag Handwerk und Technik, Hamburg 2000, pp. 154–169, ISBN 3-582-01235-2
- Bertram Schmidkonz: Practical course in inorganic analysis . Verlag Harri Deutsch, Frankfurt 2002, ISBN 3-8171-1671-3