Properties of Materials
Section: Chemistry | Syllabus: Cambridge Primary Science (0846)
Change of State Temperatures
- Substances change state when they are heated or cooled enough
- each substance has its own specific temperatures where these changes happen
- Melting point: the temperature at which a solid becomes a liquid - a property of a substance
- Boiling point: the temperature at which particles throughout a liquid have enough energy to change to a gas
| Substance | Melting Point | Boiling Point |
|---|---|---|
| Pure Water | 0 °C | 100 °C |
| Gold | 1064 °C | 2856 °C |
| Vinegar | -2 °C | 118 °C |
Melting and boiling points are different for every substance
Measuring Mass and Volume
- Mass is measured using a balance - place the object on the balance and read the value
- The volume of an irregular solid (like a rock) can be measured using the water displacement method:
- Step 1: record the water level in a measuring cylinder
- Step 2: lower the object into the water and record the new, higher water level
- Step 3: subtract the first reading from the second - the difference is the object's volume
Density and Floating
- Density compares how much mass is packed into a given volume - it affects whether an object floats or sinks in a liquid
- Dissolving a solid (like salt) in water makes the water denser
- this means an object can float higher in salty water than in plain water
Particle Size Affects Water Behaviour
- A material's particle size affects how it interacts with water - soil is a good example:
- sandy soil has large particles with big gaps, so water drains through quickly
- clay soil has very small, tightly packed particles, so it holds water rather than draining it
Hardness
- Hardness is how well a material resists being scratched - it is tested using a scratch test, for example scratching a rock with a nail
- a mark left behind shows the material is softer than what made the scratch
- Safety: when scratch-testing with something sharp like a nail, keep your other hand well away from the point, to avoid cuts
Properties of Gases
- Air is a mixture of gases - gas is one of the states of matter
- All matter has these properties:
- it takes up space
- it has mass (even though we often can't feel it unless it's moving)
- Gases take the shape of their container, and can be compressed (squashed)
The scale tips towards the full balloon, showing that air has mass
Thermal and Electrical Conductivity
- The ability to conduct heat or electricity is a property of a material
Thermal Conductors
- Heat transfer between objects is called conduction
- materials that allow heat to flow through them easily are thermal conductors
- Metals are good thermal conductors
- silver is the best conductor of heat
- Non-metals (like glass and plastic) are poor conductors (insulators)
Wax droplets melt one by one as heat is conducted along the metal rod
Comparing Thermal Conductors: Fair Test
- To compare how well different metals conduct heat, fix a small ball of wax to the end of identical spoons made of different metals, then stand them all in the same container of hot water at the same time
- keep everything else the same: the size/shape of the spoons, the amount of wax, and the water temperature
- the metal whose wax falls off first (shortest time) is the best thermal conductor - this lets you rank the metals from best to worst conductor
Electrical Conductors
- Materials that allow electricity to flow through them are electrical conductors
- To test if a material is a conductor, connect it into a circuit with a battery and a lamp
- if the lamp lights up, the material is a conductor; if it stays off, the material is an insulator
| Property | Conductor (Allows Flow) | Insulator (Blocks Flow) |
|---|---|---|
| Electrical | Metals (Copper, Gold), Graphite | Plastic, Rubber, Wood |
| Thermal (Heat) | Metals (Aluminium, Iron), Silver | Oven mitts, Polystyrene, Cork |
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