Gold
Gold is a beautiful yellow metal, which is very inert. It
does not tarnish in air at all and remains shiny almost forever. The pure metal
is quite soft, but alloys containing some silver and/or copper make the metal
much harder, making it suitable for precious jewelry. The higher the gold
content, the more precious the jewels.
Gold is not attacked by the mineral acids, nor by strong alkalies. Only a mixture of concentrated nitric acid and concentrated hydrochloric acid dissolves gold at an appreciable rate. Remarkably, gold also dissolves fairly easily in solutions of sodium cyanide or potassium cyanide, when the solution is kept in intimate contact with fresh air. This is due to formation of a cyano-complex of gold.
Gold metal can be obtained at high purity from eBay at prices, ranging from $15 to $30 per gram in the form of small bullions, as shown in the picture above. Scrap gold can also be obtained at much lower prices (sometimes as low as $1 per gram), but this scrap gold usually contains up to 40% of other metals as impurity. Refining this gold is possible for the home chemist, but it is quite cumbersome and not without risk. When one wants to experiment with gold compounds, then it is more convenient to buy gold chloride.
In its compounds, gold exists in the +1 oxidation state and the +3 oxidation state. Oxidation state +1 is unstable, unless a suitable coordinating compound is present. When oxidation state +1 is not stabilized, it quickly disproportionates to the metal and the +3 oxidation state.
For the general public the only compound of gold, which is readily available from several photography raw chemical suppliers and from several eBay vendors, is the so called 'gold chloride'. This compound is not true gold chloride, but it is an acid called chlorauric acid, its formula is HAuCl4·3H2O. This is an orange/yellow solid, which is very hygroscopic and dissolves in water very well. Solutions of this compound are deep yellow and contain ions AuCl4–.
Gold compounds are very interesting to experiment with. Gold forms many interesting and colorful complexes, it has quite some interesting redox chemistry and it forms beautiful colorful colloidal solutions in the metallic state. Unfortunately, 'gold chloride' is very expensive. It is sold for approximately $30 per gram by photography raw chemical sellers. Sometimes, with some luck, it can be obtained on eBay for less than $20 per gram, but then usually more than 1 gram needs to be purchased.