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There is a formation of silver mirror in the silver mirror test. why does the silver does not precipitate, it forms the mirror in the silver mirror test? Is there any test that copper can form mirror? Why silver can form silver mirror but copper cannot?

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    $\begingroup$ Related: Copper substituting silver in Tollen's reagent $\endgroup$ – user7951 Jan 17 '20 at 21:28
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    $\begingroup$ I see the answers focus on the easiness of reduction rather than the actual forming of a mirror. The two things might be related but, though this might be unsatisfactory, the mirror formation should depend on the stiffness and adesivity of silver to glass. Not the first things that one analises in details when doing chemistry in test tubes. $\endgroup$ – Alchimista Jan 18 '20 at 8:45
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A copper mirror can be formed, for example by reaction between $\ce{Cu(NH3)4^{2+}}$ and hydrazine in basic solution.

That being said, copper in general forms mirrors less easily than silver because copper is harder to reduce to the metal. This data page gives a standard reduction potential of about 0.34 V for reducing copper(II) to the metal but about 0.80 V for reducing silver(I).

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A copper mirror can be obtained by heating two or three grams of dry copper formate $\ce{Cu(HCOO)2}$ in a test tube with a Bunsen burner. For some reason, the copper atoms are deposited on the inner surface of the test tube. Try it! It is easy to do!

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