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Grade 7 Science

Unit 3: Mixtures & Solutions Chapter 7 Matter can be classified as mixtures or pure substances






Particle Theory of Matter

All matter is made up of tiny particles .

These particles are always moving… they have energy.

There are spaces among particles.

There are attractive forces between the particles.

The particles of one substance differ from the particles of other substances .


Page 230


Matter can be either:

Pure Mixtures substances

Mixtures are the physical combination of two or more pure substances .

 Contain only one kind of particle and are the same throughout.

Pure Substances...


ALWAYS appear as uniform throughout

They contain either:

1. Only one type of particle • Gold and Oxygen.

2. Two or more particles chemically combined to form a different substance.

• Water is H ² O which is 2 hydrogen's and 1 oxygen

Pure Substance

 Substances don’t usually occur in their pure form in nature, so in order to obtain pure substances, people must refine raw materials.

Bauxite makes Aluminum foil

Examples of Pure Substances

•sugar (C 12 H 22 O 11 ) •copper (Cu) •distilled water (H 2 O) •carbon dioxide (CO 2 ) •oxygen (O 2 ) NOTE: pure substances covered are not limited to elements.


They are the physical combination of two or more pure substances.

Sugar + Water =




 MAY have distinct visible components.

 MAY appear uniform throughout.

Six of the possible kinds of mixtures are:







a mixture of gases a mixture of liquids a mixture of gases in a liquid a mixture of solids a mixture of solids in a liquid a mixture of solids and gases

Soft drinks are mixtures made from: - liquid water - Solid sugar - Carbon dioxide gas

Commonly used mixtures

 Detergents  Cleaners – Formed by adding water to the cleaner  Gasoline – oil mixtures – Lawn mower engines require specific amounts of oil to be mixed with gas

Examples of Mixtures…

•kool-aid •chocolate chip cookie •concrete •salad dressing •Air •Bread

 For each picture find the arrow and state the kind of mixture.  Ex: mixture of gases in a liquid

Apply: The particle theory of matter

#1: All matter is made up of tiny particles.

#5: The particles of one substance differ from the particles of other substances.

1 type of particle

In class activity

T r u e F a l s e

 1. Air is a mixture. _____   2. Gold is a pure substance. _____ 3. Water from a lake is a pure substance. _____   4. A pure substance contains particles that are all alike. _____ 5. Two different gases together make up a mixture. _____  Work book: – Page 1 – 3

p. 235

Heterogeneous and homogeneous MIXTURES

What is a mechanical Mixture?

 Mixtures composed of two or more substances that remain visible even after they are mixed.

 Sometimes need a microscope (see p. 245)  Can be solid, liquid or gas  The particles do not evenly mix

 Mechanical mixtures are also known as heterogeneous mixtures (uneven mixtures). p.244

– A salad dressing made of oil and vinegar is considered a heterogeneous mixture because its components: • oil and vinegar — remain separate and distinct.

– Think about a chocolate chip cookie.

• Would it be considered a mechanical mixture?

• Why or why not? ________________________________ ________________________________

Heterogeneous Mixtures

 Example: – Smog-filled air • the amount of smog is not uniform inside the air. – Granola cereal or trail mix • the individual ingredients such as raisins, nuts, and dried fruit remain visible even after mixing. – Concrete • the components of the sand, lime, and water used to create it often remain visible.

Heterogeneous Mixtures

Granola bar

What is a Solution?

 A type of mixture in which the pure substances within the solution mix together so well that they give the appearance of only one substance.

 Solutions can be any combination of the three states of matter — solid, liquid, and gas.

 Particles appear to be mixed evenly and to be the same throughout.


Solutions are also called Homogeneous mixtures

 Examples: – When sugar is mixed with water, the sugar seems to "disappear." Yet, if you were to taste the mixture, you would know the sugar was still there. Also, if you were to place the solution in a shallow dish and allow the water to evaporate, the sugar would reappear.

– Air - dissolve carbon dioxide, oxygen, and argon into nitrogen gas. – Brass- made up of copper and zinc.

Homogeneous Mixture

 The particles are evenly mixed so that none of the original substances are visible. Stainless steel Kool-aid

Mixtures can be classified into 2 types: p.234




– A non-uniform mixing • Particles create layers or parts • May also appear as one substance • Light will scatter as it passes through • May or may not need a microscope to see parts


– A uniform mixing • Appear as one substance • Particles are evenly spread out • Light will pass through unaffected • Cannot see parts with a microscope

Illustrating the particle theory of matter. Mechanical mixture Solution

p. 235 Questions 1 – 3 p. 237 Questions 1 – 3 p. 241 Questions 1- 6 Workbook


Combination of mixtures

p. 244  Sometimes you cannot tell whether something is homogeneous or heterogeneous just by looking at it. – The mixtures are hard to classify: • Homogeneous • Heterogeneous  However, we can use light to determine…

Using light:


homogeneous and heterogeneous

Homogeneous Mixture

• They appear to be ONE substance • light passes through unaffected

Heterogeneous Mixtures

 Light will scatter because it reflects off the particles

Tyndall Effect…

Homogeneous mixture




copper (II) sulfate solution salt water sugar water

Heterogeneous mixtures

    vegetable oil and water Pepper and water sugar & vegetable oil vinegar and salad oil

Is it homogeneous or heterogeneous? Or a combination?

 A large number of mixtures are not classified as either homogeneous or heterogeneous but rather are combinations of both.

– They fall on a continuum from homogeneous to heterogeneous depending on particle size… Combination of both

Some mixtures are combinations of heterogeneous and homogeneous mixtures

 Milk  Orange juice  Soft drink  Ex: Orange juice: – Homogeneous: sugars with water – Heterogeneous: is a combination of solid orange pulp and water.

In class activity

 Name one example of a heterogeneous mixture and one example of a homogeneous mixture. – Explain how you are able to tell the two types of mixtures apart.

 Chapter review p.250 Questions 1-10  p. 245 Questions 1-4  p. 249 Questions 1-6  Workbook