Pearson International A Level Chemistry Core Practical 16: Prepare and purify aspirin

This core practical is part of Pearson's practical-learning programme. The method below is one defensible implementation, not a confidential instruction sheet. Centres may adapt equipment while preserving the scientific purpose, controls, measurements and safety requirements.

Aim and scientific principle

Synthesise, isolate and purify aspirin, then use yield and melting behaviour as complementary evidence.

Begin by translating the title into a testable question. Identify what is deliberately changed, what is measured directly, what is calculated and what must remain controlled. Predict a relationship only after naming the mechanism. A prediction without a reason is weak; a reason without measurable variables cannot guide a practical design.

Apparatus and setup

Use salicylic acid, ethanoic anhydride or specified acylating reagent, catalyst, water bath, filtration apparatus, recrystallisation solvent, balance and melting-point equipment. Select every measuring instrument by range and resolution, not by name alone. Draw a labelled scientific setup that shows the working geometry and exactly where readings are taken. Include a control or blank when it distinguishes the target effect from drift, contamination or background response.

Before collecting results, check zero readings, calibration, leaks, alignment or sterility as relevant. Record the instrument resolution beside the first raw-data table. If a digital device displays more digits than its underlying accuracy supports, do not treat every digit as equally certain.

Method

1. Measure reactants, add catalyst carefully and heat in a controlled water bath.
2. Quench as directed and cool to crystallise the crude product.
3. Collect by suction filtration, wash, recrystallise with minimum hot solvent and dry thoroughly.
4. Measure mass and melting range, then calculate percentage yield from the limiting reagent.

Plan the analysis before starting. This reveals whether an additional measurement is needed for a derived quantity and prevents a completed experiment from lacking a mass, length, concentration, background or calibration value. A method should be detailed enough for another trained student to reproduce, while avoiding decorative steps that do not affect validity.

Variables and controls

• Independent variable: reaction or recrystallisation condition if investigated.
• Dependent variable: dry product mass, percentage yield and melting range.