Density practical: solids and liquids
Measure mass and volume, process displacement readings and explain errors in density measurements.
Practise the calculations · Print a classroom set
Apparatus and measurements
Use a balance for mass. A ruler or calipers can measure the dimensions of a regular block. An irregular, non-porous solid needs a displacement measurement; a liquid needs a measured volume and its own mass.
Larger apparatus diagram
Method and controls
- Zero the balance and record the mass of a dry solid. For a rectangular block, measure three perpendicular dimensions and multiply them. Repeat dimension measurements at several positions if the faces are uneven.
- For a solid that sinks and does not dissolve, record the initial water volume, lower the solid until it is fully submerged and record the final volume. Read the bottom of the meniscus at eye level. Remove trapped air bubbles.
- For a liquid, weigh the dry empty cylinder, then weigh it with a measured volume of liquid. Subtract the empty-cylinder mass. Use mass and volume units that match the requested density unit.
Results to analyse
Original synthetic data for practice.
| Measurement | Reading |
|---|---|
| Dry solid mass / g | 156 |
| Initial water volume / cm³ | 35 |
| Final water volume / cm³ | 55 |
| Empty cylinder mass / g | 42 |
| Cylinder + liquid mass / g | 90 |
| Liquid volume / cm³ | 60 |
Questions
- Calculate the solid’s volume and density in g cm⁻³, then convert the density to kg m⁻³.
- Calculate the liquid density. Why must the container mass be subtracted?
- An air bubble remains attached to the submerged solid. Explain the likely effect on the calculated density.
Show worked answers
- Solid volume = 55 − 35 = 20 cm³. Density = 156/20 = 7.80 g cm⁻³ = 7800 kg m⁻³.
- Liquid mass = 90 − 42 = 48 g; density = 48/60 = 0.800 g cm⁻³. The container contributes mass but is outside the measured liquid volume.
- The bubble increases the apparent displaced volume. The mass is unchanged, so dividing by the larger volume gives a density that is too low.
Evaluation
A wider cylinder has larger volume increments; use a cylinder with appropriate resolution for the displacement. A small displacement found by subtracting two readings can have a large relative uncertainty.
An absorbent, soluble or floating sample needs a different method. Do not claim that the simple sinking-solid method works for every material. Keep the balance dry and avoid dropping a solid into glassware.
Specification links
AQA 8463: Required practical 5; 4.3.1.1. OCR Gateway J249: P1.1d–f; PAG P1 (selected). Selected skills only; no practical-completion assessment.
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