IGCSE Chemistry Electrolysis Notes

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Syllabus Objectives

CORE:

  • Define electrolysis as the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current
  • Identify in simple electrolytic cells:
  • (a) the anode as the positive electrode
  • (b) the cathode as the negative electrode
  • (c) the electrolyte as the molten or aqueous substance that undergoes electrolysis
  • Identify the products formed at the electrodes and describe the observations made during the electrolysis of:
  • (a) molten lead(II) bromide
  • (b) concentrated aqueous sodium chloride
  • (c) dilute sulfuric acid using inert electrodes made of platinum or carbon/ graphite
  •  State that metals or hydrogen are formed at the cathode and that non-metals (other than hydrogen) are formed at the anode
  • Predict the identity of the products at each electrode for the electrolysis of a binary compound in the molten state
  • State that metal objects are electroplated to improve their appearance and resistance to corrosion
  • Describe how metals are electroplated

EXTENDED:

  • Describe the transfer of charge during electrolysis to include:
  • (a) the movement of electrons in the external circuit
  • (b) the loss or gain of electrons at the electrodes
  • (c) the movement of ions in the electrolyte
  • Identify the products formed at the electrodes and describe the observations made during the electrolysis of aqueous copper(II) sulfate using inert carbon/ graphite electrodes and when using copper electrodes
  • Predict the identity of the products at each electrode for the electrolysis of a halide compound in dilute or concentrated aqueous solution
  • Construct ionic half-equations for reactions at the anode (to show oxidation) and at the cathode (to show reduction)

Revision Notes

IGCSE Chemistry Electrolysis Notes

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Test Your Understanding

Topic: Electrolysis

Hover over each blank to reveal the correct answer.

Definition of Electrolysis

1. Electrolysis is the ________ of an ________ compound when ________ or in ________ solution by the passage of an electric current.
2. Electrolysis only occurs when ions are free to ________.
3. The substance that is broken down during electrolysis must contain ________ ions.

Parts of an Electrolytic Cell

4. The ________ is the positive electrode in electrolysis.
5. ________ ions move towards the anode.
6. The ________ is the negative electrode in electrolysis.
7. ________ ions move towards the cathode.
8. The ________ is the molten or aqueous substance that undergoes electrolysis.
9. The electrolyte contains mobile ________ that carry electrical charge.

Products at Electrodes

10. ________ or ________ are formed at the cathode.
11. ________ (other than hydrogen) are formed at the anode.

Electrolysis of Molten Lead(II) Bromide

12. Molten lead(II) bromide contains ________ and ________ ions.
13. ________ metal forms at the cathode.
14. Observation: ________ metal deposits at the cathode.
15. ________ gas forms at the anode.
16. Observation: ________ coloured fumes are produced.

Electrolysis of Concentrated Sodium Chloride

17. Concentrated sodium chloride solution is also called ________.
18. ________ gas is produced at the cathode.
19. Observation: ________ of gas are seen.
20. ________ gas forms at the anode.
21. Observation: ________ gas is released.

Electrolysis of Dilute Sulfuric Acid

22. Dilute sulfuric acid produces ________ gas at the cathode.
23. ________ gas forms at the anode.
24. The electrodes used are usually ________ or ________.

Electroplating

25. Electroplating is used to improve the ________ of metal objects.
26. It also increases resistance to ________.
27. The object to be plated is connected to the ________.
28. The metal used for coating is connected to the ________.

Transfer of Charge

29. In the external circuit, charge is carried by ________.
30. In the electrolyte, charge is carried by ________.
31. ________ occurs at the cathode where electrons are gained.
32. ________ occurs at the anode where electrons are lost.

Half Equations

33. A half-equation shows the transfer of ________ during electrolysis.
34. At the cathode, ions ________ electrons.
35. At the anode, ions ________ electrons.
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