Here's a breakdown:
* Tollens' reagent is a solution of silver ions (Ag+) in ammonia.
* Formaldehyde (HCHO) is an aldehyde.
* The reaction: The silver ions (Ag+) in Tollens' reagent are reduced to metallic silver (Ag), forming a silver mirror on the surface of the reaction vessel. This is the characteristic observation of a positive Tollens' test.
* Oxidation of formaldehyde: Simultaneously, formaldehyde is oxidized to formate ion (HCOO-).
Overall reaction:
HCHO + 2[Ag(NH3)2]+ + 3OH- → HCOO- + 2Ag + 4NH3 + 2H2O
Key takeaway: Formaldehyde is oxidized to formate ion in the Tollens' test.
