CHEMISTRY · Stage 9 · Chapter 11: Patterns in the Periodic Table
Chemistry 11.1 Calculating density — Mass, Volume and Density Formula
5 min read 6 parts Lesson 1 of 7
Lesson summary
11.1 Calculating density — Mass, Volume and Density Formula — Alhussan International Academy — Chemistry (Stages 7–9) notes: Define density and calculate density, mass or volume for solids, liquids and gases using the correct units.Density = the mass of a material in a certain vo…
- Material property
- Conversions
- Typical values
- Solid block
- Liquid or gas
- Regular block
Part 1 of 6What density means
- Density = the mass of a material in a certain volume.
- Iron weights of mass 20 kg are heavier than aluminium weights of the same size with mass 7 kg because iron has a greater density.
- Material property — density is a property of a material, not an object, so a small and large piece of the same pure iron have the same density.
- Cubes — cubes of different metals with the same volume have different masses because their densities differ.
- Mass = the amount of matter in an object, measured in grams (g) or kilograms (kg).
- Volume = the amount of space an object takes up, measured in cm3, m3 or litres.
Part 2 of 6The density formula
1Formula2 points
— density = mass ÷ volume (ρ = m ÷ V).
- Mass = density × volume.
- Volume = mass ÷ density.
2Units
— g/cm3 when mass is in grams and volume in cm3, and kg/m3 with kilograms and cubic metres.
3Conversions
— 1 kg = 1000 g, 1 m3 = 1 000 000 cm3, and g/cm3 × 1000 = kg/m3.
4Typical values1 point
— a block of wood is about 0.5 g/cm3 and air is about 1.2 kg/m3.
- Water is 1.0 g/cm3 or 1000 kg/m3.
| Material | Density (g/cm3) |
|---|---|
| Water | 1.0 |
| Aluminium | 2.7 |
| Iron | 7.9 |
| Lead | 11.3 |
| Gold | 19.3 |
Part 3 of 6Measuring mass
- Solid block — place it directly on a balance.
- Liquid or gas — use a container.
- Find the mass of the container.
- Add the material.
- Find the mass of the container + material.
- Calculate: mass of material = (mass of container + material) - (mass of container).
Part 4 of 6Measuring volume
- Liquiduse a measuring cylinder, reading the bottom of the curved surface (meniscus) with your eye level with the scale, not from above or below.
- Regular blockvolume = width × length × height.
- Irregular solid such as a stoneuse displacement.
- Partly fill a measuring cylinder with water to a known volume.
- Add the stone.
- Measure the new volume.
- Calculate the volume increase, which is the volume of the stone.
Part 5 of 6Calculating density
- Steps — write the formula, substitute the values, and give the answer with units.
- Wood block — 270 g in 540 cm3 has a density of 0.5 g/cm3.
- Air in a room — 36 kg in 30 m3 has a density of 1.2 kg/m3.
- Identifying materials — a density value can identify an unknown material, such as iron at 7.9 g/cm3.
- Mass-volume graph — the points for a material lie on a straight line through the origin and the gradient is the density.
- A steeper line means a denser material.
- Accuracy — repeat measurements and take a mean.
Part 6 of 6Floating and sinking
- Rulean object floats in a fluid if its density is lower than the fluid's density and sinks if it is higher.
- Exampleswood (about 0.6 g/cm3) floats in water, whereas iron sinks.
- Shipsa steel ship floats because its shape holds a large volume of air, so its average density is lower than water.
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