Hydrochloric acid group
The hydrochloric acid group (HCl group) is a group of elements whose salts form poorly soluble chlorides with hydrochloric acid . In addition to silver (Ag), this also includes the two heavy metals mercury (Hg) and lead (Pb) in the form of their cations Ag + , Hg 2 2+ , Pb 2+ , as well as the rarer thallium than Tl + . These are precipitated, filtered off, separated and detected in the cation separation process of qualitative analysis (in inorganic chemistry ).
Group felling
The HCl group therefore falls out of the dissolved sample / original substance ( precipitation reaction ) when it is concentrated with the release agent. Hydrochloric acid is added, so z. B. the silver cations:
The cations of the hydrochloric acid group are separated from other, further heavy metal cations by precipitation and filtration in order to be able to detect their presence in the sample without other heavy metal cations disturbing the detection reactions. At a pH value of 0 to 3.5 the following results:
- Mercury (I) chloride - Hg 2 Cl 2
- Mercury (II) chloride - HgCl 2
- Lead (II) chloride - PbCl 2 , soluble in hot water
- Silver chloride - AgCl, as a silver diammine complex soluble in conc. Ammonia water
- Copper (I) chloride - CuCl (only under reducing conditions)
- Thallium (I) chloride - TlCl, slowly dissolves in hot water.
The cations of the following separation groups are then in the filtrate:
- Hydrogen sulfide group,
- Ammonium sulfide group,
- Ammonium carbonate group and
- Soluble group .
literature
- Michael Wächter: chemistry laboratory . Verlag Wiley-VCH, Weinheim 2011, pp. 234f, ISBN 978-3-527-32996-0
- Bertram Schmidkonz: Practical course in inorganic analysis . Verlag Harri Deutsch, Frankfurt 2002, ISBN 3-8171-1671-3
- Gerhart Jander: Introduction to the inorganic-chemical internship . S. Hirzel Verlag, Stuttgart 1990 (in 13th edition), ISBN 3-7776-0477-1
