Electrolysis Flashcards
(25 cards)
What is electrolysis?
The breakdown of a substance using electricity. It involves oxidation (loss of electrons) and reduction (gain of electrons).
What are the names of the electrodes in electrolysis?
- Cathode: Negative electrode (where reduction happens)
- Anode: Positive electrode (where oxidation happens)
What moves to each electrode in electrolysis?
- Positive ions (cations) → cathode (gain electrons, reduced)
- Negative ions (anions) → anode (lose electrons, oxidised)
What is a half-equation in electrolysis?
- It shows the gain or loss of electrons during electrolysis. Electrons are written as e⁻ to balance the charges.
Write a half-equation for sodium being oxidised.
Na → Na⁺ + e⁻
Write a half-equation for hydrogen ions being reduced.
2H⁺ + 2e⁻ → H₂
Why can molten ionic compounds be electrolysed?
Because the ions are free to move and conduct electricity.
What happens during the electrolysis of molten lead bromide (PbBr₂)?
- Cathode: Pb²⁺ + 2e⁻ → Pb
- Anode: 2Br⁻ → Br₂ + 2e⁻
What material are electrodes made of in electrolysis? Why?
Inert materials like graphite or platinum, so they don’t react.
Predict the products of molten Al₂O₃ electrolysis.
- Cathode: Al³⁺ + 3e⁻ → Al
- Anode: 2O²⁻ → O₂ + 4e⁻
What extra ions are present in aqueous solutions?
- From water: H⁺ and OH⁻
What is formed at the cathode in aqueous electrolysis?
- If metal is more reactive than H⁺ → H₂ gas
- If metal is less reactive than H⁺ → solid metal is deposited
What is formed at the anode in aqueous electrolysis?
- If halide ions (Cl⁻, Br⁻, I⁻) are present → halogen gas
- If no halide ions → oxygen gas
Electrolysis of NaCl solution: What is formed at each electrode?
- Cathode: H⁺ + e⁻ → H₂ (since Na is more reactive than H)
- Anode: 2Cl⁻ → Cl₂ + 2e⁻
What is a quick rule to predict gas at the anode in aqueous electrolysis?
- Halide present → halogen
- No halide → oxygen
Why is it important to clean electrodes before electrolysis?
To remove grease or oxide layers which can affect the experiment’s accuracy.
Setup of an electrochemical cell for aqueous electrolysis?
- Get 2 inert electrodes (e.g. graphite or platinum electrodes)
- Clean surfaces of the electrodes with emery paper (or sandpaper)
- Do not touch the surfaces with your hands -> could transfer grease back onto the strips
- Place both electrode into a beaker filled with the electrolyte
- Connect electrodes to a power supply with crocodile clips & wires -> when turned on, a current will flow through the cell
Electrolysis of aqueous copper(II) sulfate (CuSO₄) — What is the product at the cathode?
Copper (Cu) is deposited, because it is less reactive than hydrogen.
Half-equation at the cathode for CuSO₄ electrolysis?
Cu²⁺ + 2e⁻ → Cu
What is the product at the anode during CuSO₄ electrolysis?
Oxygen (O₂) — because sulfate ions (SO₄²⁻) are not discharged.
Half-equation at the anode for CuSO₄ electrolysis?
4OH⁻ → O₂ + 2H₂O + 4e⁻
2H2O(l)→O2(g)+4H + (aq)+4e −
Electrolysis of dilute sulfuric acid (H₂SO₄) — What is the product at the cathode?
Hydrogen gas (H₂) — H⁺ ions are discharged.
Half-equation at the cathode for H₂SO₄ electrolysis?
2H⁺ + 2e⁻ → H₂
What is the product at the anode during H₂SO₄ electrolysis?
Oxygen (O₂) — because sulfate ions are not discharged.
