# Copper substituting silver in Tollen's reagent

I am an artist attempting to use Tollen's Reagent in a number of my projects.

Is there any reason I could not substitute Copper Nitrate for the Silver Nitrate in the reaction? Would the copper adhere to the glass?

For the particular reaction where you get a silver mirror with an aldehyde, I doubt it'll work for copper, due to the reduction potentials. I'll take acetaldehyde $\ce{<->}$ acetate as an example here, but I believe that the reduction potentials of most aldehydes will be similar. The nitrate is a spectator ion here, so we need not consider its presence.

$$E^o_{\ce{Ag^+,Ag}}=+0.80$$ $$E^o_{\ce{Cu^{2+},Cu}}=+0.34$$

$$E^o_{\ce{CH3COO^{-},CH3CHO}}=+0.580$$

Our reaction involves the metal ($\ce{Ag}$ or $\ce{Cu}$ being reduced, so it must have a higher reduction potential than the acetate/acetaldehyde pair. Of the two metals, only silver has a higher SRP, thus the reaction involving silver nitrate is spontaneous--whereas the copper nitrate reaction is infeasible.

Of course, you could find some substrate other than an aldehyde which reacts with copper nitrate to achieve the effect you want--though I'll have to look up some stuff to figure this out. I think the Tollen's reaction is a single step everyday redox reaction, which means that we just need to look for a stronger reducing agent which doesn't harm the glass.

Actually, it looks like the standard process for plating nonconductors with metals is to give them a conducting layer by dipping them in something, and then using electroplating. Not sure about this, though.

Manishearth points to the right direction, the crucial parameters to look at are the standard electrode potentials. One should however take into account that the relevant species that get reduced under the condition of the Tollens' reagent are not the aquo- but the amine complexes, namely $\ce{[Ag(NH3)2]+}$. and $\ce{[Cu(NH3)4]^{2+}}$, respectively.

Unfortunately i don't have the data at hand.

Notably, a copper-based reagent comparable to the Tollens' reagent exists: Fehling's solution. However, in this case, Cu(II) is reduced to Cu(I) only but not to copper metal.

In the end, you just might give it a try and post the results :)

• (Note that if you're going to give it a try, copper sulphate is usually easier to get hold of and shouldn't make a difference to the reaction as far as I can tell.) – Aesin Aug 2 '12 at 9:28
• I got 'copper mirror' with Fehling's solution once, but adhesion was not best. I didn't care, thought, so this might be my fault. Anyway, Fehling's solution is much, much easier to handle then Tollen's reagent. – permeakra Aug 5 '12 at 16:30