# A New Way to Practise Percentage Purity — Without the MessGrade 11 learners doing the Quantitative Aspects experiment this term know the drill: crush the chalk, add it to the acid, watch the mass drop as CO₂ escapes, then work backwards to find how pure the sample really was. It’s a good practical, but not every learner gets a chance to repeat it enough times to feel confident with the calculation. Equipment is limited, time is limited, and the maths at the end — moles, mass, percentage — is where marks are usually lost.To help with that, there’s now an interactive simulation of the full experiment, built to match the CAPS practical exactly: same method, same variables, same formulas.## What it doesEnter a sample mass between 3,0 g and 10,0 g, just as the practical instructs, then press react. The flask fizzes, the digital balance counts down in real time as carbon dioxide escapes, and once bubbling stops, the trial gets logged automatically. Run it three times with different masses and the simulation builds a full recording table — initial mass, final mass, mass of CO₂ released, and the average.From there, it calculates moles of CO₂, converts that to mass of pure CaCO₃, and works out the percentage purity live, using the same n = m/M and 1:1 mole ratio learners are expected to apply by hand.Every run gives a slightly different purity result, somewhere between 85% and 96%, so learners can’t just memorise one answer. They have to actually work through the numbers each time.## Why this helpsMost learners understand the theory of the experiment. Where they lose marks is usually in translating a table of masses into a final purity percentage — remembering which formula applies where, and in what order. Being able to run the reaction again and again, without setting up glassware or waiting eight minutes for bubbling to stop, means more repetitions and more confidence before the real practical or the exam question that mirrors it.It’s also useful for anyone catching up after being absent, or revising before a test, without needing a lab.## Where to find itThe simulation is free to use and works on any device with a browser, phone included. [Link to be added once hosted.]As always, if you spot something that doesn’t quite match how your class did the practical, let us know — these tools get refined based on how they’re actually used in the classroom.