All 12 IGCSE Chemistry topics on one page, as things you can play with

Solid, liquid and gas differ in how the particles are arranged and move, not in the particles themselves. Slide the temperature in the first box and watch the moment the particles vibrate hard enough to leave their places. Then light the burner under the beaker of ice in the second experiment and watch the graph go flat at 0 °C and 100 °C.

The third experiment is the NH₃/HCl glass tube: cotton wool at each end, start the clock. The white ring forms nearer the HCl end because NH₃ is lighter and diffuses faster. That is the most repeated exam question in this topic.

Molecules are not flat like the page. Drag a molecule round and look at it from every side; you will see why water is bent and methane is a tetrahedron.

Bonds form in two ways: ionic means electrons are transferred, covalent means they are shared. Slide the dot-and-cross diagram and watch the electrons travel. Switch between NaCl and H₂O and compare.

The mole is the bridge between the mass you can weigh and the number of particles that actually react. Pick a substance, drag the mass, and watch the moles, particles and gas volume change together.

The second tool walks through a reacting-mass calculation in three steps. Step 2, forgetting the numbers in front of the formulae, is where most marks are lost. Switch reactions and see how the mole ratio changes the answer.

Electrolysis uses electricity to split a compound: cations to the negative electrode, anions to the positive. Simple enough, until the exam asks what forms at each electrode, and the answer depends on whether the compound is molten or dissolved.

Choose a cell, close the switch, and watch the ions move, the gas bubble and the metal plate out. Compare concentrated NaCl with CuSO₄ and see why one gives H₂ and the other Cu.

Every reaction first spends energy breaking old bonds, then gets energy back as new bonds form. The difference is ΔH, and the reaction pathway diagram is the picture this topic is examined on most.

Slide ΔH from negative to positive and watch the diagram flip from exothermic to endothermic. Then add a catalyst: Ea drops, ΔH does not move. That question comes up every year.

Start with the experiment every classroom runs: drop Mg into acid and collect the H₂ in a gas syringe. Change one thing at a time (concentration, temperature, powder or ribbon, a catalyst) and keep each curve to compare: steeper means faster, but the final volume stays the same. Then see the reason in the particle box: collision theory, where only collisions with enough energy react.

A reversible reaction has an equilibrium you can push. Using the Haber process, lower the temperature or raise the pressure and watch the share of NH₃ change. Notice the catalyst changes the speed but not the share.

A titration finds how much acid there is using a base of known concentration. Add NaOH to the flask of HCl in steps of 5, 1 and then 0.1 cm³ and watch the pH and the indicator colour.

Notice that the pH barely moves for the first 20 cm³ and then leaps within the last 0.2 cm³. That is why you go drop by drop near the end-point, and why different indicators change at different moments.

The Periodic Table is a map, not a list to memorise. Elements in a group have the same number of outer electrons, so they behave alike, which is why exams can ask you to predict an element you have never studied.

Pick a lens: metals vs non-metals, Group I, Group VII, noble gases. Tap elements 1 to 20 to see their electron shells. Notice Group I gets more reactive going down while Group VII does the opposite.

The reactivity series answers three questions at once: which metal displaces which, which react with water or acid, and which can be extracted with carbon. Memorising the order alone does not stick.

Pick a metal and drop it into a salt solution to see whether displacement happens, with the balanced equation. Try Mg in CuSO₄, then the other way round.

In the exam, climate change has to be explained as a mechanism, not as 'CO₂ is bad'. Sunlight passes through the atmosphere and warms the ground; the ground emits infrared; greenhouse gases absorb it and send some back down.

Slide the amounts of CO₂ and CH₄ and watch the share of heat trapped. Yellow lines are sunlight, red lines are infrared from the ground. See which molecules absorb which.

Organic chemistry looks like a hundred names to memorise, but there are only a few series. Members of a series differ by CH₂ each time and react the same way.

Choose alkanes, alkenes, alcohols or carboxylic acids and slide the number of carbons. The displayed formula draws itself; the molecular formula and boiling point follow. Notice why the boiling point keeps climbing.

Chromatography separates a mixture because each substance travels a different fraction of the way with the solvent. Rf is the spot's distance divided by the solvent's. Slide the time and see that Rf stays the same whenever you stop.

The last topic also carries the command words. Describe and Explain are marked differently; know the syllabus meaning first and you will neither over-answer nor under-answer.