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What are the physical and chemical reactions of gold?
Answer 1:

Gold is a noble metal, which means that is not very reactive. Some special chemistries, however, do react with gold. For example, there is an acid solution called "aqua regia." The name means "king's water" in Latin because it can dissolve the gold, which is a precious metal associated with royalty. Aqua regia is made of a boiling solution of nitric and hydrochloric acid. These acids combined react with gold and make "tetrachloroauric acid," which is a molecule containing gold and chlorine.

Some examples of physical reactions with gold include sputtering of gold and electroplating of gold. Sputtering means that the gold is vaporized and redeposited from the vapor onto a surface. Think of it as kind of like spray painting gold atoms onto a surface.

In electroplating, the gold atoms are dissolved into a water-based solution and are deposited onto the desired surface by using an electricity source like a battery to attract the gold atoms to that surface.

Answer 2:

Gold is quite stable, so as a solid chunk it doesn't react with much. This is why it has been used in currency and jewelry, because it doesn't corrode or oxidize over time. Gold is stable to even strong acids, but a special combination of nitric acid and hydrochloric acid can dissolve it. This combination is known as "aqua regia", which is latin for "royal water," because of it's special ability to dissolve gold. Gold is also able to be attacked by a couple other things, including mercury and sulfur-containing compounds. Mercury will dissolve gold, and sulfur compounds will bind to gold.

As far as physical reactions, you can heat gold up to make it melt, and it is prized for its softness even as a solid. Because it's so soft, it can easily be made into wires that are thinner than human hair, or into ultra-thin sheets that are only a few atoms thick. Pure gold is very soft, but also chemically resistant, which makes it great for dental caps, and which is why gold caps have traditionally been the best material for dental work up until recently. Now, specially-designed advanced ceramics are becoming more popular, and are much cheaper.

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