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” together forming parts for the observer to see.

Terminology What does this mean? 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!