Pearson International A Level Chemistry Core Practical 3: Find hydrochloric acid concentration by titration

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

Use quantitative transfer and a chemically justified endpoint to relate a standard amount to an unknown concentration.

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 analytical balance, volumetric flask, pipette, burette, conical flask, funnel, wash bottle and suitable indicator when required. 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. Prepare or obtain the standard solution using quantitative transfer and complete dissolution.
2. Condition the pipette and burette with their working solutions, remove funnel and air bubbles, then record initial readings.
3. Titrate while swirling, add reagent dropwise near the endpoint and record final readings to the burette precision.
4. Obtain concordant titres, calculate a mean and use the balanced redox or acid-base ratio.

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: delivered titrant volume.
• Dependent variable: defined endpoint response used to determine the reacting volume.