Grade 7 · Science · Unit 5 of 9
Particles & Mixtures
Pure substances and mixtures
What your child practises
The particle theory of matter, the states of matter, pure substances versus mixtures, and homogeneous versus heterogeneous mixtures.
Saskatchewan Curriculum outcome: MS7.1 · pure substances and mixtures using the particle model
Sample questions
A taste of this unit. In the app, questions change every time and get easier or harder to match your child.
Question 1
Pure substance or mixture? Sort each one.
Sort into: 💎 pure substance · 🥣 mixture
- 🪴garden soil
- 🍲vegetable soup
- 💧distilled water
- 🟠a copper wire
- 🌊salt water
- 🧂pure table salt
- 🟡a gold bar
- 🌬️air
Show answer
💎 pure substance: distilled water, a copper wire, pure table salt, a gold bar · 🥣 mixture: garden soil, vegetable soup, salt water, air
Hint: A pure substance is one kind of matter (an element like gold, or a compound like water). A mixture is two or more substances physically combined.
Question 2
A bottle of perfume is opened at one end of a room, and soon people at the other end can smell it. Why?
- The perfume turns into a solid
- Gas particles move randomly and spread out
- Smell particles are heavier than air
- The gas gets pushed by gravity
Show answer
Gas particles move randomly and spread out
Hint: Particles of a gas move in every direction until they are spread throughout the room.
Question 3
Why can a gas be squeezed into a smaller space more easily than a liquid?
- Gas particles are not moving
- Gas particles are very small
- There are large spaces between gas particles
- Gas particles cannot touch
Show answer
There are large spaces between gas particles
Hint: Particles in a liquid are already close together.
Question 4
Homogeneous or heterogeneous? Sort each mixture.
Sort into: 🥛 homogeneous (looks the same throughout) · 🍕 heterogeneous (different parts show)
- 🧂salt dissolved in water
- 🌬️air in a clean room
- 🥗a salad
- 🏖️iron filings mixed with sand
- 🍵tea with no leaves in it
- 🥣cereal in milk
Show answer
🥛 homogeneous (looks the same throughout): salt dissolved in water, air in a clean room, tea with no leaves in it · 🍕 heterogeneous (different parts show): a salad, iron filings mixed with sand, cereal in milk
Hint: In a homogeneous mixture the parts are evenly mixed and look like one substance. In a heterogeneous mixture you can see different parts.
Question 5
Cooking oil and water do not stay mixed. Both are pure, but together they form…
- a homogeneous mixture
- a new pure substance
- a heterogeneous mixture
- a single element
Show answer
a heterogeneous mixture
Hint: Oil floats in a separate layer, so different parts are visible.
Question 6
What is a pure substance?
- A mixture of two clean liquids
- Any clear liquid
- Any substance that is safe to drink
- Matter made of only one kind of particle
Show answer
Matter made of only one kind of particle
Hint: Gold and water are pure substances because each has one kind of particle.