= Zinc-copper displacement experiment
An inspected university demonstration makes the paired changes visible. The 2021 Chemical Demonstrations Booklet hosted by Edith Cowan University describes two cut square <zinc> strips, each immersed in a separate glass <beaker>. One contains blue <copper(II) sulfate> <chemical solution>, the other colourless <zinc sulfate> <chemical solution>. The published readouts are the appearance of a brown <copper> deposit on the first strip and fading of its blue <chemical solution>; after thirty minutes more deposit is reported. The comparison strip in <zinc sulfate> shows no visible change. The documented preparation is cutting the strips; surface polishing is not specified.<Chemical Demonstrations Booklet by Magdalena Wajrak and Tim Harrison>[Chemical Demonstrations Booklet (2021), demonstration 16, printed p. 32, “Equipment”, “Preparation”, “Observations” and Figures 1–3; p. 33, Figure 4]{ref}
The reported interpretation is conversion of dissolved $\mathrm{Cu}^{2+}$ to metallic <copper>, accompanied by conversion of metallic <zinc> to dissolved $\mathrm{Zn}^{2+}$. The <sulfate> <anions> balance bulk <electric charge> and cancel from the net <chemical equation>. The comparison shows that merely immersing a <zinc> strip in a <sulfate> <chemical solution> does not reproduce the visible coating.<Chemical Demonstrations Booklet by Magdalena Wajrak and Tim Harrison>[Demonstration 16, printed pp. 32–33: zinc-sulfate comparison and zinc/copper-sulfate equation]{ref}
Appearance is evidence for the proposed conversion, rather than a quantitative measurement of the two-<Electron> ratio. Fading alone could also reflect dilution; deposit colour alone does not independently establish its composition. A stronger follow-up would compare the <copper> content of the <chemical solution> before and after, identify the solid, and check dissolved <zinc>. These are proposed analytical checks, not results reported in the booklet. Comparable starting <chemical solutions>, surface condition, immersion and observation <time> help interpret a comparison; an unchanged-looking strip does not rule out slow or invisible <chemical reactions>.
The two-<Electron> interpretation comes from the species identities and <electric charge> balance, supported by the paired observations. It does not imply that the coating's <mass> equals the <mass> of <zinc> consumed: the same <amount of substance> of different <chemical elements> generally have different <molar masses>. Nor does it resolve microscopic surface sites or reaction pathways. The same net <redox> can be organized into separated compartments in a <Daniell cell> to obtain electrical <work>.
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