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Principles of Chemistry

Edexcel IGCSE Chemistry 4CH0 — 1.9 Electrolysis — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 5 parts Lesson 18 of 25 Unit quiz

📚 Edexcel Linear - OL (Chemistry) Hub / Topical Revision
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Lesson summary

Electrolysis practical: collect and identify products at the cathode and anode for aqueous sodium chloride, dilute sulfuric acid and copper(II) sulfate. Place the aqueous electrolyte in a beaker so that it covers two inert electrodes.

  • cathode is negative
  • anode is positive
  • pink-brown copper deposit

Part 1 of 5Set up the cell

Cathode is negative
Place the aqueous electrolyte in a beaker so that it covers two inert electrodes. Connect the electrodes to a low-voltage direct-current supply. The cathode is negative and attracts positive ions; the anode is positive and attracts negative ions.
Invert small test tubes over the electrodes to collect gases. Switch on the supply, observe each electrode and then test any collected gas. Use fresh apparatus or rinse it thoroughly when changing solutions to avoid contaminating the results.

Part 2 of 5Identify the products

Hydrogen
Hydrogen gives a squeaky pop with a lighted splint. Oxygen relights a glowing splint. Chlorine bleaches damp litmus paper. Carry out gas tests on small samples using appropriate laboratory precautions.
Copper
A solid deposit on an electrode may show that a metal has formed. A pink-brown coating on the cathode is evidence of copper.

Part 3 of 5Aqueous sodium chloride

Hydrogen
At the cathode, a colourless gas gives a pop with a lighted splint: hydrogen. At the anode, the gas bleaches damp litmus: chlorine.
Water contributes to hydrogen formation in the aqueous solution; chloride ions are discharged to form chlorine at the positive electrode. Write the observed products at their correct electrodes.

Part 4 of 5Dilute sulfuric acid

Hydrogen
At the cathode, the collected colourless gas gives a pop: hydrogen. At the anode, a colourless gas relights a glowing splint: oxygen.
The acid solution carries current through ions, while hydrogen and oxygen are the gases identified in this experiment. Keeping the electrode positions labelled avoids confusing the tests.

Part 5 of 5Copper(II) sulfate solution

1Pink-brown copper deposit
With inert electrodes, a pink-brown copper deposit appears at the cathode. The anode produces oxygen, identified because the gas relights a glowing splint.
2Check:
Check A colourless cathode gas pops, while an anode gas relights a glowing splint. Name the gases. Answer: Hydrogen at the cathode and oxygen at the anode.

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