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

Study guide01 May 2026, 00:00 ZUpdated 17 Jul 2026

Reviewed by

Azmi·Senior Chemistry Specialist

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.

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Type	What changes	Common data outcome	Paper 4 risk
Volatilisation gravimetry	A volatile product leaves the sample	Loss in mass gives amount of volatile component	Incomplete heating gives too small a mass loss
Precipitation gravimetry	An ion forms an insoluble solid	Mass of dried precipitate gives amount of ion	Product may be wet, impure, or lost during filtration

Quantity	Reading / g
Mass of empty crucible and lid
Mass of crucible, lid, and sample before heating
Mass of sample before heating
Mass of crucible, lid, and residue after heating 1
Mass of crucible, lid, and residue after heating 2
Mass of residue at constant mass
Mass lost on heating

Observation	Direction of error	Better ACE wording
Sample was not heated to constant mass	Mass loss too small	The volatile component was not fully removed, so calculated water or gas content is underestimated.
Solid spat out during heating	Mass loss too large	Some non-volatile solid was lost mechanically, so the mass decrease is not only due to the volatile product.
Residue absorbed moisture while cooling	Final mass too large	The residue gained water from air, so mass loss is underestimated.
Crucible was weighed hot	Reading unreliable	Convection currents and ongoing cooling can shift the balance reading, reducing repeatability.
Lid was left fully open during strong heating	Possible solid loss	A loosely covered crucible limits spitting while still allowing gas to escape.

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

Quick gravimetry map

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1 | What Gravimetric Analysis Means

2 | Volatilisation vs Precipitation Gravimetry

3 | Constant Mass Routine

4 | PDO Table Template

5 | Worked Calculation Pattern

6 | ACE Error Bank

7 | Planning Checklist

8 | Related Guides

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