Page 10 - Curriculum Visions Dynamic Book

The reactivity of zinc
Zinc is amphoteric, that is, it is soluble in alkalis and acids but insoluble in water. However, many of
its compounds are soluble in water. Most zinc compounds are white.
Few other common elements are more reactive than zinc. This, above all, makes zinc useful for protecting other metals, such as steel. If steel and zinc are exposed to water (which contains dissolved oxygen and carbon dioxide gas) the zinc corrodes to zinc carbonate, while the steel remains unchanged.
Reaction of zinc and copper
When a piece of zinc strip is dipped into a solution of copper sulphate, some of the zinc begins to react with it. Quite soon some of the copper in the solution
can be seen to coat the zinc and the blue
solution turns paler. Over time the zinc strip dissolves away and the solution becomes completely colourless.
The copper and the zinc have reacted so that the zinc atoms have lost electrons to the copper. As this happens the
zinc becomes soluble and the copper, which now has the same number of electrons as protons (i.e. it forms atoms), becomes insoluble and is deposited on the zinc or as a fine powder at the bottom of the dish.
Copper metal is precipitated.
EQUATION: Displacement of copper by zinc
Zinc + copper sulphate ➪ zinc sulphate + copper Zn(s) + CuSO4(aq) ➪ ZnSO4(aq) + Cu(s)
 A zinc strip is laid across a dish containing copper sulphate solution.
 The copper is precipitated on the zinc, while some of the zinc goes into solution.
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