Pearson IGCSE Chemistry Practical 2: Measurement, Apparatus and Resolution

Apparatus choice determines measurement resolution, uncertainty and whether products are collected without loss.

Written practical questions often test whether the instrument matches the quantity and required precision. The best apparatus is not automatically the one with the most decimal places: it must have a suitable range, collect the intended product and avoid introducing a larger error elsewhere.

Apparatus choices

• Select balances, thermometers and timers with suitable ranges and resolutions.
• Use measuring cylinders for routine volume, and pipettes or burettes when greater precision is required.
• Read liquid levels at eye height from the correct part of the meniscus.
• Use a gas syringe for direct gas volume and check that the system is airtight.
• Record initial and final readings rather than only their difference when the raw readings matter.
• Avoid measuring before the apparatus has reached the required starting condition.

Match apparatus to purpose

A measuring cylinder is suitable for routine liquid volumes where moderate precision is enough. A volumetric pipette delivers one fixed volume more precisely. A burette delivers a variable volume and allows an initial and final reading, making it appropriate for titration. A beaker is primarily a container and should not replace calibrated apparatus when volume is the measured variable.

A gas syringe directly measures gas volume and can collect gases that dissolve in water. Collection over water is simple and visually clear, but it is unsuitable when the gas is appreciably soluble or reacts with water. Both systems must be airtight. Check connections before the reaction, ensure the syringe plunger moves freely and keep the delivery path short enough to reduce delay.

Choose a balance whose resolution is small compared with the mass change. A $\pu{0.01 g}$ balance may be inadequate when the expected change is only a few hundredths of a gram. A thermometer must cover the expected range and have a resolution appropriate to the temperature change. A digital display does not guarantee accuracy if the probe is poorly positioned or slow to respond.