AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
When a simple ionic compound (eg lead bromide) is electrolysed in the…
Full specification wording
Electrolysis of molten ionic compounds: When a simple ionic compound (eg lead bromide) is electrolysed in the molten state using inert electrodes, the metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode.
Electrolysis of a molten simple ionic compound, such as lead bromide, uses inert electrodes to produce the metal at the cathode and the non-metal at the anode.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 1 of 2
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Electrolysis of a molten simple ionic compound, such as lead bromide, uses inert electrodes to produce the metal at the cathode and the non-metal at the anode. When lead bromide is melted, it dissociates into Pb²⁺ and Br⁻ ions. These ions are free to move and carry charge. At the negative cathode, Pb²⁺ ions gain electrons to form lead metal. At the positive anode, Br⁻ ions lose electrons to form bromine molecules. The products are lead, a silvery liquid metal, and bromine, a brown vapour. Inert electrodes, such as graphite, are used so they do not react with the products or electrolyte.
What earns the marks
- Identify the electrolyte as molten lead bromide, which contains mobile Pb²⁺ and Br⁻ ions.
- State that lead is produced at the cathode (negative electrode) as positive lead ions are attracted to it.
- State that bromine is produced at the anode (positive electrode) as negative bromide ions are attracted to it.
- Explain that inert electrodes are used so they do not participate in the reactions.
- Higher Tier only: Write the half equations for the reactions at the electrodes (e.g., Pb²⁺ + 2e⁻ → Pb).
Common mistakes and how to put them right
Confusing which product forms at which electrode.
Put it right: Metals form at the cathode; non-metals form at the anode.
Thinking that solid lead bromide can be electrolysed.
Put it right: It must be molten to allow ions to move.
Using reactive electrodes instead of inert ones.
Put it right: Inert electrodes such as graphite are used to avoid unwanted reactions.
Exam tips
- Name the products and the electrodes clearly: lead at cathode, bromine at anode.
- Explain why the compound must be molten: to free the ions so they can move to the electrodes.
Try the lesson
The start of the Electrolysis of molten ionic compounds: When a simple ionic compound (eg lead bromide) is electrolysed in the molten state using inert electrodes, the metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode. lesson, made from checked teaching notes for this specification point.
Have a go first
Molten lead bromide is electrolysed using inert electrodes. At which electrode is lead produced?
Listen
Electrolysis of a molten simple ionic compound, such as lead bromide, uses inert electrodes to produce the metal at the cathode and the non-metal at the anode. When lead bromide is melted, it dissociates into Pb²⁺ and Br⁻ ions. These ions are free to move and carry charge. At the negative cathode, Pb²⁺ ions gain electrons to form lead metal. At the positive anode, Br⁻ ions lose electrons to form bromine molecules. The products are lead, a silvery liquid metal, and bromine, a brown vapour. Inert electrodes, such as graphite, are used so they do not react with the products or electrolyte. A strong answer earns marks for these points. Identify the electrolyte as molten lead bromide, which contains mobile Pb²⁺ and Br⁻ ions. State that lead is produced at the cathode (negative electrode) as positive lead ions are attracted to it. State that bromine is produced at the anode (positive electrode) as negative bromide ions are attracted to it. Explain that inert electrodes are used so they do not participate in the reactions. A common slip: Confusing which product forms at which electrode. Instead, metals form at the cathode; non-metals form at the anode. Exam tip: Name the products and the electrodes clearly: lead at cathode, bromine at anode.
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Key words
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Electrolysis of molten compounds
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Electrode products
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Ionic mobility
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Inert electrodes
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See every definition
- Electrolysis of molten compounds
- A simple ionic compound is electrolysed in the molten state so that its ions are free to move and carry charge.
- Electrode products
- The metal is produced at the cathode and the non-metal is produced at the anode.
- Ionic mobility
- When the compound is melted it dissociates into ions, which are free to move and carry charge.
- Inert electrodes
- Electrodes such as graphite are used so they do not react with the products or electrolyte.
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