O-Level Chemistry Electrolysis & Redox Practical Guide

TL;DR
Electrolysis and redox investigations test your ability to wire cells safely, collect gases, and justify ionic equations, all within the Paper 3 MMO/PDO/ACE framework.
Planning marks require clear identification of electrodes, electrolyte composition, current control, and gas tests, while MMO/PDO focus on disciplined timing, bubble observation, and volumetric readings.
ACE commentary should reconcile observations with half-equations, quantify charge passed when data permits, and propose refinements that manage heat, electrode wear, and gas purity.

Keep the Circuit Going

Work through this electrolysis drill alongside titration, gas test, and salt-prep guides inside the O-Level Chemistry Experiments hub so Paper 3 revision stays holistic.

1 | Electrolysis in the SEAB syllabus

• The SEAB syllabus’ practical techniques and assessment guidance cover electrolysis-related skills (planning, observation/measurement, data presentation, and evaluation) and expects candidates to record observations and draw conclusions from practical evidence (SEAB syllabus).
• When planning, cite realistic school-lab apparatus from the syllabus’ apparatus/material guidance list (e.g., electrodes, power supplies, gas collection setups, and common glassware).

2 | Planning the electrolysis workflow

1. Aim & cell description. Example: “Investigate the electrolysis of aqueous copper(II) sulfate using copper electrodes.”
2. Variables. Current or voltage, duration of electrolysis, electrode surface area, electrolyte concentration, and temperature control.
3. Method outline.
   • Clean electrodes with sandpaper, rinse, and measure initial masses if required.
   • Set up the power supply with correct polarity, ensuring secure connections and a stable support stand.
   • Immerse electrodes to equal depths in the electrolyte within a beaker; switch on the power and start timing.
   • Observe colour changes, gas evolution, and electrode mass changes; collect gases over water if specified.
   • Test gases using limewater (CO₂), glowing splint (O₂), lighted splint (H₂), or litmus paper (Cl₂).
4. Risk controls. Highlight hazards from concentrated solutions, potential chlorine evolution, and the need to switch off power before adjusting electrodes.

3 | MMO & PDO essentials

• Current monitoring. Record current (A) or voltage (V) at the start and end; adjust using rheostats if provided.