430 THE ELEMENTS OF GROUPS IB AND MB
In the former, it gives precipitates with halides (except the fluoride),
cyanides, thiocyanates, chromates(VI), phosphate(V), and most ions
of organic acids. The silver salts of organic acids are obtained as
white precipitates on adding silver nitrate to a neutral solution of the
acid. These silver salts on ignition leave silver. When this reaction is
carried out quantitatively, it provides a means of determining the
basicity of the acid.
Gravimetrically, silver nitrate is used to determine the chloride
ion.
Silver nitrate is used volumetrically to estimate chloride, bromide,
cyanide and thiocyanate ions. Potassium chromate or fluorescein is
used as an indicator.
In neutral solution, the indicator is potassium chromate(VI). In
acid solution the CrO^' ion changes to Cr 2 O7~ (p. 378), and since
silver dichromate(VI) is soluble, chromate(VI) is not a suitable
indicator; other methods can be used under these conditions.
(In alkaline solution, silver(I) oxide precipitates, so silver(I) nitrate
cannot be used under these conditions.)COMPLEXES OF SILVER(I)Some of these have already been noted as 2-coordinate and linear,
for example [Ag(CN) 2 ]-, [Ag(NH 3 ) 2 ]+, [Ag(S 2 O 3 )]^3 -. Silver(I)
halides dissolve in concentrated aqueous halide solutions to give
complexes [AgX 2 ]~, [AgX 3 ]^2 ~, for example [AgCl 3 ]^2 ~.
TESTS FOR SILVER
- Hydrochloric acid or any soluble chloride gives a white
precipitate, soluble in ammonia. - Hydrogen sulphide gives a black precipitate,
- Potassium chromate(VI) gives a brick-red precipitate of silver
chromate(VI) in neutral solution.
GOLD
THE ELEMENT
Metallic gold, which is found free in nature, has always been valued
for its nobility, i.e. its resistance to chemical attack. This property
is to be expected from its position in the electrochemical series. It