Free ESAT guide
ESAT Chemistry: track particles, amounts and evidence
Choose the chemical relationship first. Keep its particle model, equation and measured quantities consistent.
Choose the next topic
Use the Chemistry topic checklist alongside the official Chemistry guide. Keep quantitative chemistry, explanations of properties, reactions and experimental evidence in your plan. Being able to name a process does not establish that you can apply it to unfamiliar conditions.
Begin with an unseen problem from a relevant topic. If you cannot set it up, use the guide to repair that specific gap, then try a different problem. Reserve complete papers for practising the decisions you make across a whole module.
Track amounts through the equation
Convert each reactant to moles before comparing it with the equation coefficients. Comparing masses alone can identify the wrong limiting reactant.
Worked example
A sample of 0.36 g of pure magnesium reacts with 20 cm3 of 1.0 mol dm−3 hydrochloric acid. Take the molar mass of magnesium as 24 g mol−1 and assume the reaction proceeds until one reactant is used up.
Mg + 2HCl → MgCl2 + H2
- Convert the magnesium. Its amount is 0.36 ÷ 24 = 0.015 mol.
- Convert the acid volume. 20 cm3 = 0.020 dm3, so the acid contains 1.0 × 0.020 = 0.020 mol of HCl.
- Apply the coefficients. Each mole of magnesium needs two moles of HCl. The available acid can react with only 0.010 mol of magnesium, so HCl is limiting.
- Find the requested quantity. The reaction produces 0.010 mol of hydrogen. The remaining magnesium is 0.015 − 0.010 = 0.005 mol, with mass 0.005 × 24 = 0.12 g.
Check the result against both reactants: 0.010 mol of magnesium consumes all 0.020 mol of HCl and leaves some magnesium. The equation relates amounts in moles; it does not say that two grams of acid react with one gram of metal.
For an impure sample, first find the mass of the reacting substance. For a stated percentage yield, calculate the theoretical product before applying the yield. Keep these two reductions separate.
Try a concentration problemConnect the model with the observation
| Task | Reasoning to make explicit |
|---|---|
| Explain a property | Name the structure, the relevant particles and the interactions between them. For electrical conduction, identify which charged particles can move in the stated physical state. |
| Track a redox change | Follow electron transfer or changes in oxidation state. Check that a proposed equation conserves atoms and total charge. |
| Interpret a rate experiment | Distinguish the amount produced from the rate of production. A steeper product-against-time graph can reach the same final amount sooner. |
| Identify a substance | Use the test conditions and the observed result together. A colour or precipitate alone may be insufficient to distinguish all the proposed substances. |
State which bond or interaction changes. Melting a simple molecular substance usually overcomes attractions between molecules; it does not break every covalent bond within them. A giant covalent structure needs a different explanation.
Repair the first incorrect step
Record a specific correction: “I used cm3 with a concentration in mol dm−3”, “I compared masses instead of mole-to-coefficient ratios”, or “I described a faster reaction as making more product”. Each points to a different practice task.
Close the solution, rebuild the method and then change the unknown quantity or experimental condition. An answer you remember is useful for checking your explanation, but an unseen problem gives better evidence of independent understanding.
Use the free revision planner to give topic repair and paper review their own sessions. Chemistry is a standard 27-question, 40-minute module without a calculator; use your approved adjusted timing where applicable.
Official free resources
The ESAT Content Specification defines the scope. The Chemistry guide, June 2025 provides explanations and exercises. Check the UAT-UK preparation page for the currently linked editions and the scope annotations on older papers.
This worked example and study method are original ESATGenius material. UAT-UK does not endorse commercial courses. Our official paper guide explains how to use the available specimens, samples and older NSAA material.