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1.9.4Principles of Chemistry

Practical: Investigate the Electrolysis of Aqueous Solutions — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 5 parts Lesson 25 of 25 Unit quiz

📚 Edexcel Linear - OL (Chemistry) Hub / Topical Revision
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Section 1 of 5Apparatus and Set-up

1.9.4 Practical: Investigate the Electrolysis of Aqueous Solutions

The aim is to find what forms at each electrode for three different solutions.

Cell
  • A beaker holds the aqueous electrolyte with the electrodes fully covered by the solution.
Electrodes
  • Inert graphite electrodes are used so that they do not react or change the products.
Gas collection
  • Two small test tubes filled with solution and inverted over the electrodes collect any gas formed.
Power supply
  • A low-voltage power pack or battery supplies direct current, with the negative terminal joined to the cathode.

Section 2 of 5Method

Each solution is tested in the same way so that results can be compared.

1
Pour the solution into the beaker and place the electrodes so that they are covered.
2
Invert a test tube full of solution over each electrode to trap gases.
3
Connect the electrodes to the power supply and switch on.
4
Observe each electrode, noting bubbles, colour changes and any solid deposited.
5
Test each gas collected, then switch off and repeat for the other solutions.

Section 3 of 5Tests and Observations

Tests and Observations
Hydrogen
  • Colourless gas at the cathode which burns with a squeaky pop when a lit splint is held at the mouth of the tube.
Oxygen
  • Colourless gas at the anode which relights a glowing splint.
Chlorine
  • Gas at the anode of sodium chloride solution which bleaches damp litmus paper.
Copper
  • A pink-brown solid coats the cathode when copper(II) sulfate solution is used.
SolutionCathodeAnode
Sodium chlorideHydrogenChlorine
Dilute sulfuric acidHydrogenOxygen
Copper(II) sulfateCopperOxygen

Section 4 of 5Conclusions and Safety

Conclusions and Safety
Pattern at cathode
  • Hydrogen forms unless the metal is less reactive than hydrogen, as copper is.
Pattern at anode
  • Chlorine forms from chloride ions; otherwise oxygen forms from water or hydroxide ions.
Chlorine hazard
  • Chlorine is toxic, so use dilute or low concentrations, small volumes and good ventilation or a fume cupboard.
Eye protection
  • Wear safety glasses throughout because acids and electrolytes can splash.

Section 5 of 5Exam Checklist & Tips

1.9.4 – Key Points for the Exam

  • Electrolyte The aqueous solution that conducts and is decomposed.
  • Inert electrode An electrode that does not react, for example graphite.
  • Cathode The negative electrode where positive ions gain electrons.
  • Anode The positive electrode where negative ions lose electrons.

Common Mistakes

  • Placing the lit splint in the liquid rather than at the mouth of the collecting tube.
  • Forgetting that two gas tubes must be set up to see both electrode products.
  • Confusing the chlorine bleaching test with the glowing splint test for oxygen.
  • Using reactive metal electrodes that take part in the reaction and change the products.

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