Specification Point 1.58C (Paper 2C Only):
Describe experiments to investigate electrolysis, using inert electrodes, of molten compounds (including Lead(II) bromide) and Aqueous solutions (including Sodium Chloride, Dilute Sulfuric Acid and Copper(II) Sulfate) and to predict the products

Electrolysis: Electrolysis is the process of using electricity to break down or decompose an ionic compound. The compound is usually dissolved in water or heated until molten.

Electrolyte: A liquid which conducts electricity.

Electrolysis of Lead (II) Bromide

Electrolysis of Molten Compounds, e.g. Lead (II) Bromide:

Electrolysis of Lead Bromide, CIE IGCSE Chemistry

The electrolysis of Lead (II) Bromide

Method:

  • Add Lead (II) Bromide into a beaker and heat so it will turn molten, allowing ions to be free to move to conduct an electric charge.
  • Add two graphite rods as the electrodes and connect this to a power pack or battery.
  • Turn on power pack or battery and allow electrolysis to take place.
  • Negative bromide ions move to the positive electrode (anode) and lose two electrons to form bromine molecules. There is bubbling at the anode as brown bromine gas is given off.
  • Positive lead ions move to the negative electrode (cathode) and gain electrons to form a grey lead metal which deposits on the surface of the electrode.

Reaction at Electrodes:

Table Electrolysis Lead II Bromide, Edexcel IGCSE Chemistry

Electrolysis of Aqueous Solutions

Rules:

  • Aqueous Solutions will always have Water (H2O)
  • H+ and OH ions from the water are involved as well.

Positive Electrode

  • OH ions and non-metal ions attracted to positive electrode.
  • Either OH or non-metal ions will lose electrons and oxygen gas or gas of non-metal in question is released E.g. Chlorine, Bromine, Nitrogen.
  • Product formed depends on which ion loses electrons more readily. 

Negative Electrode

  • H+ and metal ions attracted to the negative electrode but only one will gain electrons.
  • Either hydrogen or metal will be produced.
  • If metal is above hydrogen in reactivity series, hydrogen will be produced – bubbling will be seen at the cathode.
Electrolysis aqueous solutions, IGCSE & GCSE Chemistry revision notes

The electrolysis of aqueous solutions

Method:

  • Add aqueous solution into a beaker.
  • Add two Graphite rods as the electrodes and connect this to a power pack or battery.
  • Turn on power pack or battery and allow electrolysis to take place.

Reaction at Electrodes:

Electrolysis of Aqueous Solutions table, IGCSE & GCSE Chemistry revision notes

You might be asked how you would provide evidence for what element is deposited at the anode or cathode.

  • If the gas produced at the cathode burns with a ‘pop’ when a sample is lit with a lighted splint then the gas is hydrogen.
  • If the gas produced at the anode relights a glowing splint dipped into a sample of the gas then the gas is oxygen.

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Author: Jamie

Jamie got a First class degree in Chemistry from Oxford University before going on to teach chemistry full time as a professional tutor. He’s put together these handy revision notes to match the Edexcel IGCSE Chemistry specification so you can learn exactly what you need to know for your exams.