#chemisty

/1 Formation of Tollens’ reagent

You start with silver nitrate in water:

AgNO₃(aq) → Ag⁺(aq) + NO₃⁻(aq)

Add hydroxide first, because silver refuses to stay dissolved:

2 Ag⁺(aq) + 2 OH⁻(aq) → Ag₂O(s) + H₂O(l)

That brown precipitate is silver(I) oxide. Ugly, but temporary.

Now ammonia shows up and plays ligand:

Ag₂O(s) + 4 NH₃(aq) + H₂O(l) → 2 [Ag(NH₃)₂]⁺(aq) + 2 OH⁻(aq)

This is the important species:

[Ag(NH₃)₂]⁺ = di-ammine silver(I) complex ion

Now some. nerdy chemical things.

NH₃ is a ligand, a Lewis base donating a lone pair and Ag⁺ is a Lewis acid. The N→Ag bond is a coordinate covalent bond.

Silver(I) coordination number here is 2, which is low-key weird and makes the complex fragile. Which is why you need to spray some chemical to fix the nm thick silver coating in place.

/2 Redox reaction with an aldehyde

Generic aldehyde oxidation:

R–CHO + 2 OH⁻ → R–COO⁻ + H₂O + 2 e⁻

Silver reduction:

[Ag(NH₃)₂]⁺ + e⁻ → Ag(s) + 2 NH₃

Combine them (multiply silver half-reaction by 2):

R–CHO + 2 [Ag(NH₃)₂]⁺ + 3 OH⁻ → R–COO⁻ + 2 Ag(s) + 4 NH₃ + 2 H₂O