AQA A-level Chemistry required practicals
There are 12: here is what exam questions ask about each one and where marks are lost.
Try the free titration walkthrough1Prepare a volumetric solution and perform an acid–base titration
Exam questions ask: The mass weighed, the flask volume, burette readings and the mean titre, then the concentration from the mole ratio.
Where marks go: Rinsing with the wrong liquid, overshooting the end point, an air bubble in the burette tip, or reading the scale at an angle.
2Measure an enthalpy change
Exam questions ask: The temperature change, q = mcΔT, then the enthalpy change per mole with its sign.
Where marks go: Using the mass of the solid instead of the solution, dropping the negative sign, or ignoring heat lost to the surroundings.
3Investigate the effect of temperature on reaction rate
Exam questions ask: A rate from 1/time at each temperature, with the same amount reacting every time.
Where marks go: Changing the concentration or volume between runs, or reading a longer time as a faster rate.
4Identify specified inorganic ions with test-tube reactions
Exam questions ask: The reagent, the observation and the ionic equation for each ion test.
Where marks go: Acidifying with hydrochloric acid before silver nitrate, which adds chloride, or with sulfuric acid before a sulfate test.
5Distil a product made in a reaction
Exam questions ask: The temperature range to collect, and why distilling removes the product as it forms.
Where marks go: Confusing distillation with reflux, heating a sealed apparatus, or running the condenser water the wrong way.
6Test for alcohols, aldehydes, alkenes and carboxylic acids
Exam questions ask: Positive and negative observations for each test, using a second test when one is not enough.
Where marks go: Expecting acidified dichromate to change colour with every alcohol, or naming only an ion instead of the full reagent.
7Measure rates using both an initial-rate method and continuous monitoring
Exam questions ask: Orders from initial rates, the rate equation, k with its units, and a gradient from a tangent.
Where marks go: Taking orders from the balanced equation, or joining two points instead of drawing a tangent.
8Measure electrochemical-cell EMF
Exam questions ask: The cell potential with its sign, the cell diagram, half-equations and the overall reaction.
Where marks go: Saying electrons flow through the salt bridge (ions do), or using a salt bridge that reacts with the solutions.
9Track pH for both weak-acid/strong-base and strong-acid/weak-base reactions
Exam questions ask: The pH curve, the equivalence point and the right indicator for each titration.
Where marks go: Assuming the equivalence point is always at pH 7.
10Prepare a pure organic solid, test its purity, and prepare a pure organic liquid
Exam questions ask: Percentage yield, the melting point against the data value, and evidence that the liquid is pure.
Where marks go: Keeping the wrong layer or filtrate, or confusing a drying agent with a dehydration reaction.
Walkthrough: Solid: prepare, recrystallise, test purityWalkthrough: Liquid: prepare, separate, dry, distil
11Identify aqueous transition-metal ions using test-tube reactions
Exam questions ask: Colours, precipitates and what happens with excess reagent, with balanced equations.
Where marks go: Mixing up the iron(II) and iron(III) precipitates, or what copper(II) does with a little and with excess ammonia.
12Separate species using thin-layer chromatography
Exam questions ask: Distances from the baseline to each spot and to the solvent front, and the Rf values.
Where marks go: Putting the solvent above the baseline, or comparing Rf values run under different conditions.