ElectrolysisDefinitions

Key Definitions

Part of Electrolysis of Aqueous Solutions · GCSE GCSE Chemistry revision

This definitions covers Key Definitions within Electrolysis of Aqueous Solutions for GCSE Chemistry. Revise Electrolysis of Aqueous Solutions in Electrolysis for GCSE Chemistry with 21 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 5 of 13 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.

Topic position

Section 5 of 13

Practice

21 questions

Recall

15 flashcards

📖 Key Definitions

Aqueous solution: A substance dissolved in water. In electrolysis of aqueous solutions, both the ions from the dissolved salt AND H⁺ and OH⁻ ions from water are present.

Preferential discharge: When two ions compete at an electrode, the one that is more easily reduced (at cathode) or more easily oxidised (at anode) is discharged first.

Discharge: When an ion gains or loses electrons at an electrode and becomes a neutral atom or molecule — it is "discharged" from ionic to uncharged form.

Brine: A concentrated solution of sodium chloride (salt) in water. Electrolysis of brine produces hydrogen, chlorine, and sodium hydroxide — the chlor-alkali industry.

Half equation (cathode for H₂): 2H⁺ + 2e⁻ → H₂

Half equation (anode for O₂): 4OH⁻ → O₂ + 2H₂O + 4e⁻

Keep building this topic

Read this section alongside the surrounding pages in Electrolysis of Aqueous Solutions. That gives you the full topic sequence instead of a single isolated revision point.

The Two Decision Rules — Learn These!Key Facts to Memorise The Water Complication Electrolysis of Brine — Click to Explore

Practice Questions for Electrolysis of Aqueous Solutions

When sodium chloride (NaCl) is dissolved in water, which four types of ion are present in the solution?

A. Na⁺, Cl⁻, H⁺ and OH⁻
B. Na⁺, Cl⁻, H₂O and OH⁻
C. Na⁺, Cl⁻ only
D. Na⁺, Cl⁻, H₂ and O²⁻

1 markfoundation

Describe the three products formed when concentrated brine is electrolysed, and state where each is produced.

3 marksstandard

Quick Recall Flashcards

State the anode rule for aqueous electrolysis.

If a halide ion (Cl⁻, Br⁻, or I⁻) is present → the halogen gas forms. If NO halide is present → oxygen gas forms from the OH⁻ ions. Example: Cl⁻ present → Cl₂ forms. SO₄²⁻ present (no halide) → O₂ forms.

State the cathode rule for aqueous electrolysis.

If the metal is MORE reactive than hydrogen (above H in reactivity series) → hydrogen gas forms. If the metal is LESS reactive than hydrogen (below H) → the metal deposits. Examples: Na above H → H₂ forms. Cu below H → Cu deposits.

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Key Facts to Memorise