I did an experiment in class combining the aqueous solutions of $\ce{AgNO3}$ and $\ce{NaOH}$. I predicted that $\ce{AgOH}$ would form but it didn't, instead a brown precipitate. I found out it was silver oxide. But why does this happen?

I researched and found out that silver is a noble metal and is thus resistant to oxidation, so why is it oxidised in this case?

Also why is $\ce{AgOH}$ not formed? I looked at the reactivity series and apparently silver can't displace $\ce{H+}$ ions out of solution, is that why?

  • 3
    $\begingroup$ It's not oxidised. This is just a precipitation reaction. $\endgroup$
    – bon
    Sep 23 '15 at 10:10
  • $\begingroup$ oh. but then why is $\ce{Ag2O}$ formed instead of AgOH? $\endgroup$
    – Gabrielle
    Sep 23 '15 at 10:20

Silver in silver oxide is no more oxidized than in $\ce{AgNO3}$. So you should ask yourself the same question earlier, even before the reaction. Yes, noble metals are somewhat resistant to oxidation. But still they can be oxidized, and thus can form compounds, of which $\ce{AgNO3}$ and $\ce{Ag2O}$ are the examples.

Even gold can be oxidized, though that requires some extreme measures.

As to the formation of oxide instead of hydroxide, there is no clear-cut distinction between Ag and the rest of metals. Many insoluble hydroxides are not quite stable. $\ce{Cu(OH)2}$, for example, would slowly lose water and turn into oxide; likewise, $\ce{Fe(OH)3}$ turns into $\ce{FeO(OH)}$. Silver does the same, just a little faster.


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