1. Pure Substances and Mixtures and Mechanical Solutions
Grade 7 Science - Willis
Pure Substances and Mixtures
Lesson 2

2. Learning Goals I can distinguish between pure substances and mixtures.
I can use the particle theory to describe the difference between pure substances and mixtures.
I can distinguish between solutions and mechanical mixtures.

3. Pure Substances and Mixtures
Pure substances: matter that contains only one kind of particle
E.g.: tin foil, table sugar, distilled water, salt
Mixture: matter than contains two or more pure substances mixed together
E.g.: salt water, batteries, milk, air

4. Pure Substances and Mixtures
Is apple juice a pure substance or a mixture? Discuss
(Answer next page)

5. Pure Substances and Mixtures
Apple juice is a mixture of water particles, sugar particles, flavour particles and vitamin particles all mixed together.

6. Mechanical Mixtures and Solutions
Scientists classify mixtures into two main groups:
1. Mechanical Mixtures (also called heterogeneous mixture): a mixture with different parts that you can see. E.g.: cereal bars, omelettes, cookies
2. Solutions (also called homogeneous mixture): a mixture that looks like a single pure substance – uniform in appearance. E.g. tea, salt water, paint

7. Mechanical Mixtures and Solutions
Solutions can be in any three states: solid, liquid or gas, but only one state is visible at a time.
Mechanical mixtures can include different states in one mixture. (Think of breakfast cereal!)

8. Particles of Mixtures
It may surprise you that clear apple juice, air and steel are homogeneous mixtures, not pure substances!
Why?
In a solution, the different kinds of particles are mixed together evenly.
In a mechanical mixture, the different kinds of particles stay together in groups and are distributed unevenly. As a result, when you look at a mechanical mixture you can usually see the different kinds of matter.

9. Particles of Mixtures

10. Classifying Matter MATTER Pure Substances Mixtures Mechanical Mixtures
Solutions
Pure Substances

11. Video! Bill Nye on atoms!
Bill Nye - Atoms Part 1