Starter quiz
- Which subatomic particle has a negative charge?
- electron ✓
- neutron
- proton
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- What is an electrolyte?
- a gas that reacts with electrodes, producing ions
- a liquid or solution that contains freely moving ions ✓
- a solid that conducts electricity, providing a circuit
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- Which ion is discharged at the cathode during the electrolysis of aqueous solutions?
- chloride ion (Cl⁻)
- hydrogen ion (H⁺) ✓
- sodium ion (Na⁺)
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- Which of the following definitions of oxidation are correct?
- gain of electrons
- loss of electrons ✓
- gain of oxygen ✓
- loss of oxygen
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- What determines whether hydrogen or a metal is produced at the anode during electrolysis?
- the position of the metal in the reactivity series ✓
- the concentration of the electrolyte
- the amount of electricity used
- the type of electrode material
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- What is produced at the anode during the electrolysis of an aqueous solution?
- a metal
- oxygen or a halogen ✓
- hydrogen
- an alloy
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Exit quiz
- What ions are present in a solution of brine?
- H⁺, OH⁻, K⁺, Cl⁻
- H⁺, OH⁻, Na⁺, Br⁻
- H⁺, OH⁻, Na⁺, Cl⁻ ✓
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- What is produced at the negative electrode during the electrolysis of brine?
- chlorine gas
- hydrogen gas ✓
- sodium hydroxide
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- What is the half-equation for the reaction at the anode during electrolysis of brine?
- 2Cl⁻ → Cl₂ + 2e⁻ ✓
- 2H⁺ + 2e⁻ → H₂
- Na⁺ + OH⁻ → NaOH
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- How can you test for hydrogen gas?
- Bleach litmus paper.
- Perform a 'pop' test with a lit splint. ✓
- Use pH paper.
- Relight a glowing splint.
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- Why does the electrolyte become alkaline during the electrolysis of brine?
- because chlorine ions are discharged at the anode
- because hydrogen ions are discharged at the cathode
- because sodium hydroxide forms in the solution ✓
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- Which of the following statements describes what happens during the electrolysis of brine?
- Sodium metal is produced at the anode.
- Hydrogen ions are oxidised at the cathode.
- Chlorine gas is produced at the anode. ✓
- Hydroxide ions remain in the electrolysis cell at the end of the reaction. ✓
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Worksheet
Presentation
Video
Lesson Details
Key learning 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.
- 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.
Common misconception
Pupils find it hard to remember what is formed at each electrode.
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.
Keywords
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.