A student investigates the electrical conductivity and chemical changes of four liquid samples, PPP, QQQ, RRR, and SSS, using inert carbon electrodes connected to a low-voltage d.c. power supply. The student's observations are recorded in the table below.
| Liquid sample | Current flow detected | Observations at negative electrode (cathode) | Observations at positive electrode (anode) |
|---|---|---|---|
| PPP | Yes (0.45 A) | Shiny grey liquid forms | Red-brown gas evolved |
| QQQ | No (0.00 A) | No visible change | No visible change |
| RRR | Yes (0.60 A) | Colourless gas evolved | Pale green gas evolved |
| SSS | No (0.00 A) | No visible change | No visible change |
Identify which of the liquid samples are electrolytes, and justify your answer using evidence from the table.
83 exam-style questions on Edexcel GCSE Chemistry 4.2 Electrolytic processes, covering 4.2.1 Electrolytes and the process of electrolysis, 4.2.2 Products of electrolysis using inert electrodes, 4.2.3 Half equations, oxidation and reduction in electrolysis, and 4.2.4 Electrolysis of copper sulfate and purifying copper. Each one has a worked solution and a mark scheme showing where the marks go.