Identification of zinc/aluminium/magnesium with copper sulphate solution We are doing an experiment and would like to be able to identify zinc/aluminium/ magnesium . Would a copper sulphate solution work ? I hear that it turns black on contact with zinc, stays clear on contact with aluminium and fizzes on contact with magnesium.
If you mean identification of the metals in their elemental form, then yes, it might be possible to distinguish between them with an aqueous $\ce{CuSO4}$ solution due to the different reactions.

Zinc in $\ce{CuSO4}$ will be oxidized to colorless $\ce{Zn^2+}$, while $\ce{Cu^2+}$ is reduced to elemental copper, because copper is the more noble metal. The $\ce{Cu}$ precipitate is normally not black, although it can appear dark in the background of the blue solution. It can also form a layer on the piece of zinc, and in the course of the reaction, the initially blue solution will become more and more colorless.

$$\ce{Zn + CuSO4 \rightarrow Cu\downarrow + ZnSO4}$$

Aluminium does not react at all because it is protected by its native oxide layer which is stable in this solution. Magnesium, however, is oxidized under evolution of $\ce{H2}$ gas, which fizzes off from the solution because it is poorly soluble in water. The reaction will gradually become slower when insoluble $\ce{Mg(OH)2}$ passivates the metal surface.

$$\ce{Mg + 2 H2O \rightarrow Mg(OH)2 + H2\uparrow}$$