ELECTROPLATING WITH ZINC
Introduction
Electroplating is a very useful technique which uses electrolysis to coat one metal with a thin layer of another, by
making the object the cathode in an electrolytic cell.
However, with more reactive metals such as zinc, the EO values make this difficult meaning that we have to find
alternatives if wish to plate them.
In this experiment you will be electroplating a copper coin with zinc, and then heating the plated coin to form a
thin layer of a zinc-copper alloy.
Equipment and materials
Standard lab glassware
Heating kit
Tongs
Balance
Thin metal wire
Sodium hydroxide pellets (CORROSIVE)
5x1 cm strip (ish) of zinc foil
Steel wool
Distilled water
Copper coins
Task
1. Dissolve 24 g of sodium hydroxide in 100 cm3 of distilled water in a 250 cm3 beaker, stirring continuously. The
solution will get warm and is CORROSIVE.
2. Heat the solution to near boiling point on a Bunsen burner (caution: the hot solution is HIGHLY CORROSIVE,
EXERCISE CAUTION).
3. Turn the Bunsen off.
4. Add the zinc foil and stir until bubbling ceases…add more if it fully dissolves.
5. Clean a ‘copper’ coin with steel wool until it is shiny.
6. Place a copper coin in the solution so that it is touching the zinc
7. Leave the coin until it is plated with a shiny coat of zinc
8. Remove the coin and rinse it under the tap to clean it.
9. Repeat steps 7-8 with a coin that isn’t touching the zinc directly but is connected by a thin piece of metal wire.
10. Using tongs or forceps, hold the plated coin in the upper part of a roaring Bunsen flame for a few seconds until
the surface turns gold, then repeat on the other side. Heating for too long will cause the coin to tarnish.
Analysis
11. Write out a balanced equation describing the formation of the sodium zincate (Na2Zn(OH)4)
12. Write an equation describing what you think is happening in the electroplating reaction (it will help to think in
terms of voltaic cells!), and then explain why this happens.
13. How does the alloy form – what do you think happens when you heat the coin? What might you call the alloy
formed?
14. Why could we not electroplate our coin by simply electrolysing it in an aqueous solution of zinc chloride? Use
numerical values to support your answer.
15. Research some commercial applications of electroplating.
Source: RSC, http://www.rsc.org/learn-chemistry/wiki/TeacherExpt:Turning_copper_coins_into_'silver'_and_'gold'