The Tollens' test is a chemical reaction that distinguishes aldehydes from ketones because aldehydes may be oxidized to a carboxylic acid whereas ketones cannot. The aldehyde is oxidized to a carboxylic acid using Tollens' reagent, which is a combination of silver nitrate and ammonia. Ag+, the silver ion, is converted to Ag, solid silver (s). The solid silver generates a silver mirror-like layer on the inner wall of the test tube. Ketones do not react with Tollen's reagent and so do not produce a silver mirror on the test tube walls.