1. Unit 3: Mixtures & Solutions:
Grade 7 Science
Unit 3:
Mixtures & Solutions:

2. Particle Theory of Matter
1. All matter is made up of tiny particles.
2. These particles are always moving… they have energy.
3. There are spaces among particles.
4. There are attractive forces between the particles.
5. The particles of one substance differ from the particles of other substances.

3. We can classify matter as: a pure substance or as a mixture.
Classifying Matter
We can classify matter as:
a pure substance or
as a mixture.

4. Mixtures + = Sugar Water
Mixtures contain two or more different kinds of particles.
MAY appear the same throughout
MAY have distinct visible parts + =
Sugar and water
Sugar
Water

5. Examples of Mixtures… salt water, Kool-Aid chocolate chip cookie
muddy water
salad dressing
air

6. Pure Substances...
Pure substances are made up of only one type of particle and therefore look the same all throughout.

7. Examples of Pure Substances
sugar (C12H22O11)
gold (Au), copper (Cu)
distilled water (H2O)
carbon dioxide (CO2)
oxygen (O2)

8. Mixtures: Mixtures may be: Homogeneous (also called solutions) Or
Heterogeneous (also called mechanical mixtures)

9. Homogeneous Mixtures
These mixtures appear to be the same throughout and often have the same properties:
-only one part visible (appears to be one substance)
-usually transparent
-light passes through unaffected
- particles do not settle, they dissolve

10. the particles are evenly mixed so that none of the original substances are visible (dissolved)
Kool-aid

11. Homogeneous Mixture can be: solid liquid or gas Stainless steel
Salt water
Clean air

12. More Examples of Homogeneous Mixtures
Apple juice
Kool aid
Salt water
Stainless steel
Brass
Clean air

13. Heterogeneous Mixtures
Have different visible parts, each with their own properties
- two or more parts visible to the eye
- not transparent
- particles settle and they do not evenly mix
-Light will scatter

14. Heterogeneous Mixtures
can include:
solids
liquids or
gases
Granola bar
Oil and vinegar
Polluted air

15. Examples of Heterogeneous Mixtures
Sand and water
Granola bar
Tossed salad
Pizza
Cement
Polluted air
Oil and vinegar
Salad dressing

16. Homogeneous or Heterogeneous
3 techniques can be used to distinguish between the two:
Use a microscope. A solution contains only one type of particle
Use a filter. If anything gets caught in the filter it is a mechanical mixture.
Tyndall effect. Mixtures scatter the light (you can see it ) and solutions do not scatter light (you cannot see it).

17. Tyndall Effect
The tyndall effect can be used to tell the difference between a solution and a mixture.
cannot be used to distinguish between a solution and a pure liquid
How?
If you shine a beam of light directly through a mixture and you do not see the beam, it is probably a solution. The particles are evenly mixed at the molecular level so they will not block or scatter the light.
Left: Silver colloid mixture
Right: Tap water

18. In a Solution...
Light passes unaffected (if a student looks at the beaker perpendicular to the direction of the beam they will NOT see it

19. In a Mechanical Mixture...
The light will scatter as it passes through the mixture because all particles are not dissolved (as shown on the left)

20. Mechanical Mixture or Solution?

21. Flow Chart Matter Pure Mixture Heterogeneous Homogeneous
Mechanical Solution
mixture

22. Some mixtures may be both homogeneous and heterogeneous
Example: orange juice
The large pulp particles make it a heterogeneous and the sugar molecules dissolved in it make it homogeneous.

23. Colloids
A colloid is a type of mixture that appears to be a solution but it is actually a mechanical mixture

24. Solid Sol Examples: cranberry glass, ruby glass
Examples of colloids
Dispersed medium
Gas
Liquid
Solid
Continuous
Medium Gas
NONE (All gases are mutually miscible)
Liquid Aerosol Examples: fog, mist
Solid aerosol Examples: smoke, air particulates
Foam Examples: whipped cream
Emulsion Examples: mayonnaise, hand cream
Sol Examples: milk, paint, pigmented ink
Solid Foam Examples: aerogel, styrofoam, pumice
Gel Examples: butter, gelatin, jelly, cheese, opal
Solid Sol Examples: cranberry glass, ruby glass

25. Suspensions
Suspensions are a heterogenous fluid containing solid particles will settle over time if left undisturbed
Examples:
Mud or muddy water, is where soil, clay, or silt particles are suspended in water.
Flour suspended in water
Fog is water suspended in air.
Paint
Chalk powder suspended in water.
Dust particles suspended in air.