Electrolysis of molten salts
Lesson details
Learning outcome
I can explain why salts can be electrolysed when in their liquid state, and describe the reactions taking place.
Key learning points
- A solid ionic compound cannot conduct electricity.
- Salts are ionic compounds which can be electrolysed when they are in the molten state.
- Gases may be formed at the electrodes.
- Freely moving ions can reach the electrodes and undergo oxidation or reduction.
- A non-metal always forms at the positive electrode, and a metal forms at the negative electrode.
Keywords
Molten - the term used to describe a liquid substance formed by heating ionic compounds and metal ores.
Anode - A positively charged electrode, in an electrolysis cell, to which the anions are attracted.
Cathode - A negatively charged electrode, in an electrolysis cell, to which the cations are attracted.
Anion - A negatively charged ion.
Cation - A positively charged ion.
Common misconception
Pupils often think that, during electrolysis, the charge carriers are electrons and not ions.
Revisit the structure of ionic compounds in the solid and liquid states. Point out that there are no delocalised electrons. The electrons are associated with ions and so are unable to move through the electrolyte. Ions can move in the liquid state.
Teacher tip
Demonstrate or show a video of the electrolysis of molten zinc chloride. Point out that the bulb only lights up when all the solid has melted.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is an ion?
Q2.When metal atoms react to form ions they ...
Q3.Which of the following elements form negatively charged ions?
Q4.How does a sodium atom become a sodium ion (Na⁺)?
Q5. What is the total charge of an ionic compound?
Q6.What is electrolysis?
Assessment exit quiz
6 Questions
Q1.What happens when molten calcium chloride is electrolysed?
Q2.What state must salts be in to conduct electricity for electrolysis?
Q3.What is produced at the cathode during the electrolysis of molten sodium chloride?
Q4.Why can molten salts conduct electricity?
Q5.What happens to cations during electrolysis?
Q6.What is the overall charge of the products formed during electrolysis?
To help you plan your 11 chemistry lesson on: Electrolysis of molten salts, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 11 chemistry lesson on: Electrolysis of molten salts, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
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Explore more key stage 4 chemistry lessons from the Electrolysis unit, dive into the full secondary chemistry curriculum, or learn more about lesson planning.