The scammers used aluminum alloy to impersonate metal silver, and used copper silver to impersonate gold. How to use chemical methods to expose him?

The first type can be tested with hydrochloric acid. Silver is not lively metal and does not react with hydrochloric acid. If it is aluminum, the hydrochloric acid will be replaced with hydrogen, and bubbles will emerge, which is easy to distinguish.
The second type should be identified with nitric acid. Copper and silver non -lively metal react with strong oxide nitric acid, which produces gas, mainly NO2 and NO. NO contacts oxygen also quickly becomes NO2. NO2 has red -brown, irritating odor, and easy to identify. Gold disagreement with simple nitric acid. When nitric acid and hydrochloric acid are mixed with 1: 3, the king water can be made to corrode gold. Therefore, it is enough to distinguish the authenticity of gold.