Pearson International A Level Chemistry Core Practical 1: Measure the molar volume of a gas

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

Generate a known amount of gas, measure its volume and relate corrected gas volume to moles under stated conditions.

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 reactant of known amount, reaction vessel, gas syringe or inverted measuring cylinder, balance, thermometer and pressure information. 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 a limiting reactant accurately and assemble an airtight gas-collection system.
2. Mix reactants without losing the initial gas and allow the reaction to finish.
3. Record gas volume, temperature and pressure where required, and repeat with a leak check.
4. Use the balanced equation to find gas moles and calculate molar volume for the stated conditions.

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: amount of limiting reactant when a proportionality is investigated.
• Dependent variable: collected gas volume.