Exercise Solutions Available
Step-by-step answers for all textbook questions in this chapter
Why Do We Sort Materials?
We group materials to study them easily, find common properties, and use them for the right purposes. No single property is used to sort — we use many properties together.
Properties Used to Sort Materials
1. Appearance (Lustre)
- Lustrous materials have a shiny surface — metals like gold, silver, iron.
- Non-lustrous materials have a dull surface — wood, plastic, stone.
2. Hardness
- Hard materials resist scratching — iron, stone, diamond.
- Soft materials are easily scratched or compressed — cotton, foam, rubber.
3. Solubility in Water
| Soluble (dissolves) | Insoluble (does not dissolve) |
|---|---|
| Salt | Sand |
| Sugar | Chalk |
| Copper sulphate | Oil |
Note: Oil does not mix with water. When shaken, it forms a layer on top.
4. Transparency
| Type | Description | Examples |
|---|---|---|
| Transparent | All light passes through | Clear glass, clean water, air |
| Translucent | Some light passes through | Frosted glass, oiled paper, butter paper |
| Opaque | No light passes through | Wood, metal, cardboard, stone |
5. Float or Sink in Water
| Float | Sink |
|---|---|
| Wood | Stone |
| Plastic bottle (empty) | Iron nail |
| Feather | Coin |
| Leaf | Marble |
Why? Objects less dense than water float. Objects more dense than water sink.
6. Magnetic or Non-magnetic
| Attracted to Magnet | Not Attracted |
|---|---|
| Iron | Wood |
| Nickel | Plastic |
| Cobalt | Aluminium |
| Steel | Copper |
Remember: Not all metals are magnetic. Copper, aluminium, and gold are metals but not attracted to magnets.
Materials and Their States
Materials can be:
- Solid — fixed shape and volume (stone, wood, iron)
- Liquid — fixed volume, no fixed shape (water, oil, milk)
- Gas — no fixed shape or volume (air, steam)
Grouping by Appearance
We can group materials as:
- Rough or Smooth — sandpaper (rough), glass (smooth)
- Shiny or Dull — gold (shiny), chalk (dull)
- Coloured or Colourless — copper (coloured), water (colourless)
Key Vocabulary
| Term | Meaning |
|---|---|
| Transparent | Allows all light to pass |
| Translucent | Allows some light to pass |
| Opaque | Blocks all light |
| Soluble | Dissolves in a liquid |
| Insoluble | Does not dissolve |
| Lustrous | Shiny |
| Magnetic | Attracted to a magnet |
Exam Tips
- The transparent–translucent–opaque distinction appears almost every year — learn all three with 2 examples each.
- Not all metals are magnetic — copper, aluminium are metals but not magnetic. This is a common tricky question.
- Oil is insoluble in water and floats on top — mention this in solubility answers.
- Give examples from daily life — examiners award marks for relevant examples.
Frequently Asked Questions
Transparent materials allow all light to pass through (clear glass, water). Translucent materials allow only some light to pass (frosted glass, oiled paper). Opaque materials do not allow any light to pass (wood, metal, stone).