Electrolysis of solutions sim
Predict the product at each electrode for nine solutions, switch on, test the gases with splints and litmus, weigh the copper, and compare what you predicted with what you saw.
Electrolysis: predicting and testing the products from aqueous solutions · covers the O-Level, IGCSE, GCSE topic
What the sim shows
In electrolysis, positive ions move to the cathode, where one kind gains electrons (reduction); negative ions move to the anode, where one kind loses electrons (oxidation). In a solution, water also provides hydrogen ions and hydroxide ions, so there is a choice of ions to discharge at each electrode. At the cathode: the metal is deposited if it is less reactive than hydrogen (copper); otherwise hydrogen is given off. At an inert anode: a halide gives the halogen (chlorine, bromine or iodine) if it is concentrated enough; otherwise, as with sulfate, oxygen is given off from hydroxide ions. With copper electrodes in copper(II) sulfate, the copper anode dissolves instead and the cathode gains the mass the anode loses. The amounts (beyond the syllabus; shown so the volumes are real): moles of electrons = current × time divided by 96500 C/mol; hydrogen and chlorine take 2 electrons per molecule, oxygen 4, copper 2; gases at 24.0 dm³/mol. So water gives hydrogen and oxygen in a 2 : 1 ratio by volume. Tests: hydrogen gives a squeaky pop with a lighted splint; oxygen relights a glowing splint; chlorine turns damp blue litmus red, then bleaches it. Time moves only when you press Run 1 minute. Model limits: the currents are illustrative; chlorine is fairly soluble, so the tube collects 90 % of what is made; for sodium chloride, the share of chlorine at the anode (the rest is oxygen) rises with concentration, as c divided by (c + 0.5) for c in mol/dm³, an illustrative curve; above about 0.5 mol/dm³ the gas is mostly chlorine.
- Cathode (−, left) and anode (+, right): carbon, or copper
- Balance: weigh the cathode before and after
- Tests: lighted splint, glowing splint, damp blue litmus
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