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11.1Chapter 11: Patterns in the Periodic Table

Calculating density — Alhussan Chemistry - Stage 9 Revision Notes & Topical Questions

5 min read 8 parts Lesson 1 of 7 1 quiz

📚 Alhussan Chemistry - Stage 9 Hub / Topical Revision
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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
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
  • 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 cubes of different metals with the same volume have different masses because their densities differ.
Mass
Mass the amount of matter in an object, measured in grams (g) or kilograms (kg).
Volume
Volume the amount of space an object takes up, measured in cm3, m3 or litres.

Part 2 of 6The density formula

Formula
  • Formula density = mass ÷ volume (ρ = m ÷ V).
  • Mass = density × volume.
  • Volume = mass ÷ density.
Units
  • Units g/cm3 when mass is in grams and volume in cm3, and kg/m3 with kilograms and cubic metres.
Conversions
  • 1 kg = 1000 g, 1 m3 = 1 000 000 cm3, and g/cm3 × 1000 = kg/m3.
Typical values
  • Typical values 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.
MaterialDensity (g/cm3)
Water1.0
Aluminium2.7
Iron7.9
Lead11.3
Gold19.3

Part 3 of 6Measuring mass

Solid block
  • Solid block place it directly on a balance.
Liquid or gas
  • Liquid or gas use a container.
1
Find the mass of the container.
2
Add the material.
3
Find the mass of the container + material.
4
Calculate: mass of material = (mass of container + material) - (mass of container).

Part 4 of 6Measuring volume

Measuring volume
Liquid
  • Liquid use a measuring cylinder, reading the bottom of the curved surface (meniscus) with your eye level with the scale, not from above or below.
Regular block
  • Regular block volume = width × length × height.
Irregular solid such as a stone
  • Irregular solid such as a stone use displacement.
1
Partly fill a measuring cylinder with water to a known volume.
2
Add the stone.
3
Measure the new volume.
4
Calculate the volume increase, which is the volume of the stone.

Part 5 of 6Calculating density

1Steps
  • Steps write the formula, substitute the values, and give the answer with units.
2Wood block
  • 270 g in 540 cm3 has a density of 0.5 g/cm3.
3Air in a room
  • 36 kg in 30 m3 has a density of 1.2 kg/m3.
4Identifying materials
  • Identifying materials a density value can identify an unknown material, such as iron at 7.9 g/cm3.
5Mass-volume graph
  • 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.
6Accuracy
  • Accuracy repeat measurements and take a mean.

Part 6 of 6Floating and sinking

Rule
  • Rule an object floats in a fluid if its density is lower than the fluid's density and sinks if it is higher.
Examples
  • Examples wood (about 0.6 g/cm3) floats in water, whereas iron sinks.
Ships
  • Ships a steel ship floats because its shape holds a large volume of air, so its average density is lower than water.

Key terms

TermMeaning
Densitythe mass per unit volume of a material.
Massthe amount of matter in an object, measured in kg or g.
Volumethe space taken up by an object.
Floatto stay on the surface of a fluid because of lower density.
Displacementusing the rise in water level to find the volume of an irregular solid.
Meniscusthe curved surface of a liquid in a measuring cylinder.

Avoid these mistakes

1
Mixing grams with cubic metres in the same calculation — convert so the units match.
2
Dividing volume by mass — density is mass divided by volume.
3
Thinking bigger objects always have greater density — density depends on the material.
4
Leaving out the units in the answer — always include g/cm3 or kg/m3.

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