Gravimetric Analysis for H2 Chemistry Paper 4: Volatilisation, Constant Mass, and ACE Errors

Q: What does H2 Chemistry gravimetric analysis test?
A: It tests whether you can use mass change to determine composition or purity, while controlling heating, cooling, weighing, and constant-mass technique.

TL;DR
In volatilisation gravimetry, a sample is heated so a volatile component leaves. The remaining solid is cooled and weighed repeatedly until constant mass is reached. Paper 4 marks come from the method as much as the calculation: heat gently at first, cool before weighing, repeat until mass change is negligible, and explain how incomplete decomposition, moisture uptake, or solid loss affects the result.

Quick gravimetry map

• Mass change tells amount: Decide whether mass lost or residue mass is useful.
• Constant mass proves the heating step is complete enough: Heat, cool, weigh, then repeat.
• The method and error direction matter as much as the mole calculation: Link incomplete heating, moisture, or solid loss to the final result.

Concrete example: If a hydrated salt loses water on heating, the mass lost gives moles of water. Constant mass tells you the water loss has stopped within the balance precision.

Pair this guide with the H2 Chemistry practicals hub, H2 Chemistry Paper 4 format guide, and PDO and uncertainty masterclass.

Status: SEAB H2 Chemistry 9476 syllabus checked 2026-05-01. The syllabus lists gravimetric analysis, including volatilisation gravimetry, in the Practical Assessment scope. Actual yearly apparatus requirements still depend on Confidential Instructions, so treat this as preparation for a technique family, not a prediction.

1 | What Gravimetric Analysis Means

Gravimetric analysis uses mass to infer an amount of substance. In H2 Chemistry Paper 4, the task may be practical, data-based, or a planning and evaluation context.

The common school-lab pattern is volatilisation gravimetry:

1. Measure the mass of an empty container.
2. Add the sample and measure the combined mass.
3. Heat the sample so a volatile component leaves.
4. Cool the container.
5. Reweigh.
6. Repeat heating, cooling, and weighing until the mass is constant.

The chemistry could involve water of crystallisation leaving a hydrated salt, a carbonate decomposing, or a volatile impurity being removed. The exact reaction matters less than the discipline of mass measurement.