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Year 11 - Science

Electrolysis: brine

Electrolysis

Unit Summary

This unit focuses on electrolysis, electrode reactions, and predicting products, including competing reactions in solutions. It explains metal extraction through electrolysis and writing ionic equations. It also covers tests for gases like oxygen, hydrogen, carbon dioxide, and chlorine.

Lesson Summary

You will learn to describe the reactions of electrolysis of an aqueous solution of sodium chloride, including the tests for identifying the products.

Key Notes

  • There are four ions present in a solution of brine: H⁺, OH⁻, Na⁺ and Cl⁻.
  • The product at the negative electrode is hydrogen gas.
  • The product at the positive electrode is chlorine gas.
  • Sodium hydroxide solution forms in the electrolyte solution, making it alkaline.
  • Two types of ions are in competition at each electrode.

Vocabulary To Learn

  • brine: A concentrated aqueous solution containing between 3.5% and 26% sodium chloride.
  • 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.
  • reduction: Reduction is a type of reaction in which a substance loses oxygen or gains electrons.
  • oxidation: Oxidation is a type of reaction in which a substance gains oxygen or loses electrons.

Common Mistakes To Avoid

  • Pupils find it hard to remember what is formed at each electrode.

3 Quick Questions (With Answers)

1. Explain the scientific idea in this lesson using two key points.

There are four ions present in a solution of brine: H⁺, OH⁻, Na⁺ and Cl⁻. The product at the negative electrode is hydrogen gas.

2. Define this scientific word and use it in context. 'brine'

A concentrated aqueous solution containing between 3.5% and 26% sodium chloride. Include the word in a full scientific explanation, not as a single label.

3. Correct this common scientific misunderstanding.

Mistake: Pupils find it hard to remember what is formed at each electrode. Correction: Remind pupils about the electrolysis rules and provide opportunities for them to apply the rules to different electrolytes. Use animations to show the ions present in brine and how they move in the electrolysis cell.

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