The Particle Theory of Matter

Heterogeneous and Homogenous Mixtures The Particle Theory of Matter

Outcomes • This slide show covers the following course outcomes (refer to your “Outcomes” handout for Unit 3): • 3.6 • 3.7 • 3.8 • 3.9 • 3.10

Homogeneous Mixtures • As we already learned, homogeneous mixtures contain two or more substances that combine to look like one substance. • Homogeneous mixtures are also called solutions. • Examples:

Homogeneous Mixtures • Q: Why do some substances combine to form solutions? • A: To answer this question, consider a salt water solution. • Salt is added to water. • The salt particles are attracted to the water particles and completely intermingle (mix) with the water particles. • To an observer, the particles are so intermingled that is appears as one substance.

Terminology • In salt water, the salt particles were attracted to the water particles causing them to completely mix. • This process is called dissolving. • The salt is known as the solute (the substance that dissolves). • The water is known as the solvent (the substance in which the solute dissolves). • Since the salt dissolves in the water, we say that the salt is soluble in water. • Using these terms, write a description for a solution of your choice.

Heterogeneous Mixtures • A heterogeneous mixture is a combination of two or more different types of matter that retain their own properties and that can be detected quite easily. • These mixtures may also be known as mechanical mixtures. • Examples:

Heterogeneous Mixtures • Q: Why do some substances combine to form mechanical mixtures? • A: Consider the mixture of pepper and water. • Pepper is added to the water • The pepper particles are more attracted to themselves than they are to the water particles. • The pepper particles “clump” togetherforming parts for the observer to see.

Terminology • Pepper does NOT dissolve in water. • Here, we say that the pepper is insoluble in water. • Example: Oil is soluble in gasoline but insoluble in water. • What does this mean? • Oil dissolves in gasoline because the oil particles are attracted to the gasoline particles. Oil is the solute while gasoline is the solvent. • Oil does not dissolve in water (oil particles are not attracted to the water particles). The oil and water do not mix.

Solution or Mechanical Mixture? • Q: How can you distinguish between a solution and a mechanical mixture? • A: The textbook discusses four methods: • Look at the mixture: • If you can see the different parts of the mixture, it is a mechanical mixture. • Use a microscope: • If you see only one type of mixture, it is a solution.

Solution or Mechanical Mixture? • Filtration: • If the mixture is a liquid, pour it through a filter. If there is a residue, it is a mechanical mixture (see page 247, Activity 7-2B). • Residue is the substance that is left behind in the filter. • The filtrate is the substance that passes through the filter. • Shine a light through the mixture: • Solutions do NOT scatter light, so you should not see a beam of light as it passes through (see page 246, Activity 7-2A).

Mixtures that are Mixtures • Q: Is orange juice a solution or a mechanical mixture? • A: This answer depends on whether the orange juice has pulp. • Without pulp, orange juice is a solution. • Q: Does this mean that with pulp the orange juice is considered a mechanical mixture? • NO! Scientists consider orange juice with pulp to be a mixture of mixtures. The juice is considered a solution while the juice and pulp is a mechanical mixture. It’s both! • Q: What are some more examples of mixtures that are mixtures? (See page 245 and 248)

Review • Read pages 242-249 • Check Concepts • P. 249: #1, 2, 3, 4, and 5

Assignment • Read chapter 7, p.230-248. • Review slide shows 3 & 4. • Complete #1-10, p.250-251 and #1 on p.274. • The due date will be assigned by your teacher!

The Particle Theory of Matter