Chapter 3

1. Chapter 3 Section 3.3: Mixtures of Matter

2. Objectives • Contrast mixtures and substances. • Classify mixtures as homogeneous or heterogeneous. • List and describe several techniques used to separate mixtures.

3. Matter Substance Mixture Element Compound Homogeneous Heterogeneous Recall . . . Anything that has mass and takes up space Matter that has a uniform, unchanging composition

4. Mixtures: 4-part Definition • A mixture is a physicalcombination of 2 or more substances. There are no chemical bonds between the substances. No reaction has occurred between them. • The substances in a mixture retain their own properties. The almonds in the candy mix are still almonds and the raisins are still raisins!

5. Mixtures: 4-part Definition (cont.) • The composition of a mixture is variable. Iron nitrate and water, for example, can be combined to form an infinite number of mixtures. Two of them are shown below. • The substances in a mixture can be separated by physical means. Since there has been no chemical reaction between them, no chemical reaction is needed to separate the substances.

6. Heterogeneous A mixture that is not blended smoothly throughout. The individual substances in the mixture are easily distinguishable. Examples are sand & water and orange juice with pulp. Homogeneous A mixture that has a constant composition throughout. Every drop of the mixture will have the same relative amounts of its components. Homogeneous mixtures are also called solutions. Examples are salt water and lemonade. Types of Mixtures

7. Solutions • There are 6 types of solutions systems. Refer to pg. 81, Table 3. • Note that a “solid in a solid” solution is called an alloy. • Specifically, an alloy is a homogeneous mixture of metals or of a metal and a nonmetal, with the metal the major component. • An alloy combines the beneficial properties of different metals to achieve greater strength and /or durability. • Stainless steel is an alloy of iron, chromium, and nickel. Other examples are brass (copper & zinc) and bronze (copper, zinc, and tin).

8. Physical Separation of Mixtures • Substances in a mixture are separated by physical processes. These are based on differences in the physical properties of the substances. • Differences in color, shape, or size are used to separate different stones in a gravel sample. • Since oil willfloat on top of water, oil & water can be separated because of differences indensity.

9. Physical Separation of Mixtures (cont.) • Iron can be separated out of a solid mixture because it is attracted to a magnet.

10. Physical Separation of Mixtures (cont.) • Substances, like table salt, that are soluble in water can be separated from other solids by simply adding water. • The salt can then be separated from the water by distillation. Distillation is a technique that separates the components of solutions based on differences in their boiling points.

11. Physical Separation of Mixtures (cont.) • Filtration uses a screen or filter (any porous barrier) to separate the differently-sized components of a heterogeneous mixture. Smaller particles will pass through but larger ones will be trapped by a filter.

12. Physical Separation of Mixtures (cont.) • In paper chromatography, a mixture of substances will separate out on paper primarily due to the tendency of each to be attracted to and travel across the surface of another material.

13. Physical Separation of Mixtures (cont.) Crystallizationis a separation technique for homogenous mixtures that results in the formation of pure solid particles from a solution containing the dissolved substance. In rock candy, for example, as water evaporates from a sugar water solution, the solution becomes more concentrated. The amount of water present cannot keep all the sugar in the solution dissolved. The sugar therefore crystallizes on the string.

14. Physical Separation of Mixtures (cont.) • Sublimationis the process of a solid changing directly to a gas, which can be used to separate mixtures of solids when one sublimates and the other does not.