Where is electrolysis actually used in industry, and how does electroplating put a thin metal coat on an object?
Describe everyday and industrial uses of electrolysis, including electroplating, and explain how an object is electroplated with a chosen metal
A focused answer to the N(A) Chemistry outcome on uses of electrolysis. Extracting reactive metals, purifying copper, and electroplating, plus the simple set-up that coats an object with a chosen metal.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
The syllabus wants you to describe uses of electrolysis, both industrial and everyday, including electroplating, and to explain how an object is plated with a chosen metal. The thread running through every use is the same idea from earlier: positive ions are deposited at the negative cathode, so by choosing the electrolyte and making the object the cathode, you control which metal coats it.
The answer
Extracting reactive metals
Metals more reactive than carbon, such as aluminium and sodium, cannot be extracted by heating their ores with carbon. Instead they are obtained by electrolysis of their molten compounds. This is the main industrial use of electrolysis and the only practical way to win these reactive metals.
Purifying copper
Copper for electrical wiring must be very pure. Impure copper is purified by electrolysis: pure copper is deposited on the cathode while the impurities drop away. This gives the high-purity copper that good electrical conductors need.
Electroplating: what it is
Electroplating is using electrolysis to put a thin layer of one metal onto the surface of another object. The object is made the cathode, and the electrolyte is a solution of the metal you want to coat with. We electroplate to:
- make objects look more attractive (for example silver-plated cutlery),
- protect the metal underneath from corrosion or rusting,
- give a harder or more hard-wearing surface.
How electroplating works
The object to be coated is connected as the cathode (negative). The electrolyte contains the positive ions of the plating metal. These positive ions are attracted to the negative cathode, where they gain electrons and are deposited as a thin, even coat of metal on the object. Often the anode is made of the same metal, so it dissolves to keep topping up the ions in the solution.
Examples in context
Example 1. Chrome-plated taps and trim. Bathroom taps and car parts are often chrome-plated to make them shiny and to protect the cheaper metal underneath from rusting. The object is the cathode in a chromium-containing electrolyte, a direct everyday use of electroplating.
Example 2. Tin-plated food cans. Steel cans are coated with a thin layer of tin by electroplating, because tin does not react with food and resists corrosion. This keeps food safe while using cheap steel for strength, showing how plating combines the best of two metals.
Try this
Q1. State whether an object to be electroplated is connected as the cathode or the anode. [1 mark]
- Cue. It is connected as the cathode (the negative electrode), so positive metal ions are attracted to it.
Q2. Give two reasons why an object might be electroplated. [2 marks]
- Cue. Any two of: to improve its appearance, to protect it from corrosion or rusting, or to give a harder, more hard-wearing surface.
Q3. Explain why aluminium is extracted using electrolysis instead of heating its ore with carbon. [2 marks]
- Cue. Aluminium is more reactive than carbon, so carbon cannot displace it; electrolysis is needed to break down its compound.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original5 marksA steel spoon is to be electroplated with silver. (a) State which electrode the spoon must be (cathode or anode). (b) State a suitable electrolyte. (c) Explain why the object to be plated is connected as you stated in part (a).Show worked answer →
(a) The spoon must be the cathode (the negative electrode).
(b) A solution containing silver ions, such as silver nitrate solution, is a suitable electrolyte.
(c) The silver ions in the solution are positive, so they are attracted to the negative cathode. The object is made the cathode so the silver is deposited onto it, coating it.
What markers reward: spoon as the cathode, a silver-containing electrolyte, and positive silver ions attracted to the negative cathode where they coat the object.
Original4 marksGive two reasons why objects are electroplated, and state one reason aluminium is extracted by electrolysis rather than by heating with carbon.Show worked answer →
Two reasons for electroplating (any two): to make the object look more attractive (decoration); to protect the metal underneath from corrosion or rusting; to give a harder or more hard-wearing surface; or to use a cheaper metal underneath while showing a coat of a more expensive one.
Aluminium is extracted by electrolysis because it is more reactive than carbon, so heating with carbon does not work; electrolysis is needed to break down its compound.
What markers reward: two sensible reasons for plating, and aluminium being too reactive for carbon so electrolysis is used.
Related dot points
- Describe electrolysis of a molten binary ionic compound, name the electrodes and products, and explain why the compound must be molten
A focused answer to the N(A) Chemistry outcome on electrolysis of molten compounds. The electrodes, why the compound must be melted, and how to predict the metal at the cathode and the non-metal at the anode.
- Describe electrolysis of aqueous solutions, predict the products using reactivity, and explain the part played by water at the electrodes
A focused answer to the N(A) Chemistry outcome on electrolysis of solutions. Why water means hydrogen or oxygen can form, simple rules using the reactivity series, and worked predictions for common salt solutions.
- Relate the method of extracting a metal to its reactivity, describe the extraction of iron in the blast furnace, and explain the rusting of iron and how to prevent it
A focused answer to the N(A) Chemistry outcome on extracting metals and corrosion. Linking the extraction method to reactivity, the extraction of iron in the blast furnace, the conditions needed for rusting, and ways to prevent it.
- Describe the general physical properties of metals, explain what an alloy is, and explain why alloys are often harder and more useful than pure metals
A focused answer to the N(A) Chemistry outcome on metals and alloys. The general physical properties of metals, what an alloy is, and why mixing in other atoms makes alloys harder and more useful than pure metals.
- State the reactivity series, compare the reactions of metals with water and acid, and use the series to predict displacement reactions
A focused answer to the N(A) Chemistry outcome on the reactivity series. The order of common metals, how their reactions with water and acid compare, and how to use the series to predict displacement reactions.