I was wondering what salts of gold are soluble and which are insoluble. From what I understand, silver is soluble as silver nitrate but insoluble as most other common salts like chlorides and sulphates. How does this work with gold? I was also wondering if there are any rules for solubility of salts, or whether there is some explanation for the solubility that would help in guessing the solubility of a salt?
I started thinking about this because of a question I came across in which there was a mixture of gold, silver and copper to which hot concentrated nitric acid was added, and an undissolved residue of given mass remained. Then $\ce{HCl}$ was added and more precipitate was formed. The question asked you to find the percentage by mass of gold, silver and copper. Judging by the general solubility trend of these metals, I'm guessing the first precipitate was gold and the second silver, but I was also wondering if there are some solubility rules...