New
New
Year 11
OCR
Foundation

Electrolysis: brine

I can describe the reactions of electrolysis of an aqueous solution of sodium chloride, including the tests for identifying the products.

New
New
Year 11
OCR
Foundation

Electrolysis: brine

I can describe the reactions of electrolysis of an aqueous solution of sodium chloride, including the tests for identifying the products.

Lesson details

Key learning points

  1. There are four ions present in a solution of brine: H⁺, OH⁻, Na⁺ and Cl⁻.
  2. The product at the negative electrode is hydrogen gas.
  3. The product at the positive electrode is chlorine gas.
  4. Sodium hydroxide solution forms in the electrolyte solution, making it alkaline.
  5. 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.

Provide opportunities for pupils to carry out the electrolysis of brine for themselves.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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6 Questions

Q1.
Which subatomic particle has a negative charge?
Correct answer: electron
neutron
proton
Q2.
What is an electrolyte?
a gas that reacts with electrodes, producing ions
Correct answer: a liquid or solution that contains freely moving ions
a solid that conducts electricity, providing a circuit
Q3.
Which ion is discharged at the cathode during the electrolysis of aqueous solutions?
chloride ion (Cl⁻)
Correct answer: hydrogen ion (H⁺)
sodium ion (Na⁺)
Q4.
Which of the following definitions of oxidation are correct?
gain of electrons
Correct answer: loss of electrons
Correct answer: gain of oxygen
loss of oxygen
Q5.
What determines whether hydrogen or a metal is produced at the anode during electrolysis?
Correct answer: the position of the metal in the reactivity series
the concentration of the electrolyte
the amount of electricity used
the type of electrode material
Q6.
What is produced at the anode during the electrolysis of an aqueous solution?
a metal
Correct answer: oxygen or a halogen
hydrogen
an alloy

6 Questions

Q1.
What ions are present in a solution of brine?
H⁺, OH⁻, K⁺, Cl⁻
H⁺, OH⁻, Na⁺, Br⁻
Correct answer: H⁺, OH⁻, Na⁺, Cl⁻
Q2.
What is produced at the negative electrode during the electrolysis of brine?
chlorine gas
Correct answer: hydrogen gas
sodium hydroxide
Q3.
What is the half-equation for the reaction at the anode during electrolysis of brine?
Correct answer: 2Cl⁻ → Cl₂ + 2e⁻
2H⁺ + 2e⁻ → H₂
Na⁺ + OH⁻ → NaOH
Q4.
How can you test for hydrogen gas?
Bleach litmus paper.
Correct answer: Perform a 'pop' test with a lit splint.
Use pH paper.
Relight a glowing splint.
Q5.
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
Correct answer: because sodium hydroxide forms in the solution
Q6.
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.
Correct answer: Chlorine gas is produced at the anode.
Correct answer: Hydroxide ions remain in the electrolysis cell at the end of the reaction.