Silver
Silver is a well-known precious metal, which is fairly
inert. For this reason it is used in jewelry. It also sometimes is used because
of its excellent conductivity for electrical current.
Silver utensils and jewelry slowly tarnish, due to formation of a dark sulfide layer. Silver is quite susceptible to formation of sulfide. The metal, however, is resistant against aerial oxidation and it also resists attack by water, non-oxidizing acids and alkalies. When the metal is added to concentrated nitric acid, then it readily dissolves.
A very important application of silver and its compounds is in photography. Black and white images are made of very fine silver grains in a gelatin layer. Very finely divided silver is black. Color photography also depends on the light sensitive properties of silver compounds.
Silver metal can be obtained at high purity from eBay at prices, ranging from $0.50 to $2 per gram. However, it is more interesting to purchase silver compounds.
In its compounds, silver primarily exists in the +1 oxidation state, but it can also be in the +2 and +3 oxidation states, but the latter are rare. For the general public, only two compounds of silver, both at oxidation state +1, are available readily. These are
- silver nitrate, AgNO3
- silver oxide, Ag2O
Silver (III) compounds can be made by the home chemist in aqueous solution and as a precipitate, but isolation of the pure compounds is very difficult and probably beyond the possibilities for the home lab. With a strong oxidizer like sodium persulfate, brown solutions, containing silver (III) can be prepared. In alkaline solutions, the black precipitate AgAgO2 can be prepared, with one Ag-atom in the +1 oxidation state and the other in the +3 oxidation state.
Silver nitrate is a white or transparent crystalline solid, which is available
from photography raw chemical suppliers and from some (but not all) ceramics
supply shops. Silver nitrate is soluble in water, forming colorless solutions.
The metal can easily be separated from such solutions, even by mildly reducing
agents. The metal precipitates as a coarse black precipitate. Silver ions form
light sensitive precipitates with many anionic species, among them are chloride,
bromide, iodide, but also carbonate. Silver nitrate can be used for many
interesting redox experiments and it can be used for nice mirror experiments. It
is a nice addition for the home lab. At small quantities, silver nitrate has a
price of $0.70 - $1.5 per gram, depending on purity. Having 10 to 20 grams is
sufficient for the average home lab.
Silver (I) oxide is a black solid, which only very sparingly dissolves in water,
but which easily dissolves in dilute nitric acid or a solution of sulfamic acid.
It does not dissolve in hydrochloric acid, because of formation of a precipitate
of silver chloride and it only dissolves with difficulty in dilute sulphuric
acid, because of the low solubility of silver sulfate. When silver nitrate is
not available, then the purchase of silver (I) oxide may be an option. This
compound has a price of $1 - $2 per gram.
Solutions,
containing silver (I) ions, are quite caustic. They produce black stains on the
skin and on many other organic materials, which cannot easily be removed. Silver
(I) is fairly toxic. Silver waste must be brought to a proper waste processing
facility.
Silver (I) ion
forms a colorless complex with ammonia, which on standing can be converted to a
very unstable solid, which may explode even on the slightest perturbation.
Ammoniacal solutions of silver salts may develop a crust on their surface. The
slightest wrinkling of such a crust causes it to explode. Never allow
alkaline solutions of silver (I) compounds with ammonia to stand for more than
one hour. If there is some silver waste in the form of such solutions, add
excess acid to them, in order to neutralize the ammonia. With ammonium ion, such
complexes are not formed.