Simulation of Rate of reaction measurement using syringe and disappearing cross
What the simulation does
The Rates of Reaction simulation covers the AQA GCSE Chemistry required practical, letting pupils investigate how the concentration of acid affects how fast a reaction goes. It offers two standard methods through tabs at the top.
In the disappearing cross method, sodium thiosulfate reacts with hydrochloric acid to make a cloudy yellow sulfur precipitate (Na₂S₂O₃ + 2HCl produces NaCl, S, SO₂ and H₂O). A black cross printed on a card sits under the conical flask. Pupils watch through the flask as the mixture clouds over, and a real digital stop clock counts up on screen alongside a visibility bar showing how obscured the cross has become. The cross stays fully visible for a genuine wait before it begins to fade, and pupils can only stop the timer once it has actually disappeared, so they practise the judgement the real practical demands.
In the gas volume method, magnesium ribbon reacts with hydrochloric acid to give hydrogen gas (Mg + 2HCl produces MgCl₂ + H₂). The apparatus matches the standard diagram with an orange stopper, a delivery tube and a gas syringe with sharp calibration. Gas collects over a fixed time window and the plunger slides out along the scale, giving a volume the pupils can read off.
For both methods pupils choose one of three acid concentrations (0.5, 1.0 or 2.0 mol/dm³). The results card then shows the measurement, works through the rate calculation (rate equals 1 divided by time for the cross method, or mean rate equals volume divided by time for the gas method), and keeps a running comparison table across all three concentrations so pupils build the pattern themselves. A collision theory explanation ties the result back to particle behaviour.
The simulation runs in the ClassAdapt house style with the light high contrast default, the dark navy Adapt toggle, Lexend throughout, and the full Adapt accessibility suite including the no drag buttons only mode, colour overlays, reading ruler, text sizing and colour vision filters.
Suggested class activity
Title: Which concentration wins? Predicting and testing reaction rate
Learning outcome: pupils explain, using collision theory, how increasing concentration increases the rate of reaction, and they process rate data correctly.
Starter, about five minutes. Ask pupils to predict, before touching the simulation, which of the three concentrations will react fastest and to write one sentence saying why. Collect a few predictions on the board without confirming them.
Main task, about twenty five minutes. Working in pairs, pupils run the disappearing cross method at all three concentrations, recording the time and calculating the rate for each in a results table. They repeat the lowest and highest concentrations a second time to see how close their two readings are, which opens a natural discussion about the difficulty of judging exactly when the cross has gone. Stronger pupils then switch to the gas volume method and check whether the same concentration ordering appears, giving them two independent lines of evidence for the same conclusion.
Processing, about ten minutes. Pupils sketch a bar chart of rate against concentration from their table, then write a conclusion in the form “as concentration increased, the rate increased because…”, completing it with a collision theory explanation about more frequent collisions in a more crowded solution.
Plenary, about five minutes. Pose an extension question: if they warmed the acid instead of changing its concentration, what would happen to the rate and why? This links the lesson forward to the temperature factor.
Adaptation built in. Pupils who find hand timing difficult can use the no drag buttons only mode and the enlarged stop clock, and the visibility bar gives a second, non colour cue for judging when the cross has gone. The running results table means pupils who work more slowly still see the full comparison even if they complete fewer repeats.