To learn to distinguish between mixtures and pure substances.

1. Objectives • To learn to distinguish between mixtures and pure substances. • To identify homogeneous and heterogeneous mixtures. Question: Does matter most commonly occur as pure substances or mixtures?

2. A. Mixtures and Pure Substances • Matter can be classified as a mixture or a pure substance.

3. A. Mixtures and Pure Substances Mixtures • Combination of 2 or more pure substances (elements and compounds) Examples: wood, gasoline, soil, air • Variable composition –the proportions of the components of the mixture can vary Examples: Milk – whole, 1 %, 2 %, skim, lowfat, etc.

4. Mixtures • Can be separated into individual pure substances by physical methods. Mixtures Homogeneous Heterogeneous Homogeneous – visibly indistinguishable parts (a solution) Heterogeneous – visibly distinguishable parts

5. Mixtures Examples of Homogeneous Mixtures: • Air – solution of gases (nitrogen, oxygen, carbon dioxide, helium, argon, etc.) • Wine – solution of liquids (water, ethanol, etc.) • Brass – solution of metals (copper and zinc) • Saltwater – water and salts Examples of Heterogeneous Mixtures • Sand and water • Sedimentary rock

6. Water is a compound. All the components are the same—H2O molecules. A. Mixtures and Pure Substances Pure Substances • A pure substance always has the same composition. • Pure substances are of two types: • Elements which cannot be broken down chemically into simpler substances • Compounds which can be chemically broken down into elements

7. Separation of Mixtures • Mixtures can be separated into pure substances by various means. • Separations are based on differences in physical properties • magnetism • mass • solubility • states of matter • boiling point • size

8. B. Separation of Mixtures • distillation • Can be used to separate homogeneous liquid mixtures • Mixtures are separated because parts of the mixture have different boiling points

9. B. Separation of Mixtures • filtration • Can be used to separate heterogeneous solid, liquid, and gas mixtures • Used to separate solids from mixtures

10. Separation of a Mixture Crystallization  Description: A liquid solution is heated until the liquid boils. Solids are left behind. For example, a saltwater solution can be separated by heating the solution in a beaker on a hotplate. The water evaporates and solid salt is left behind on the beaker. • Used to separate homogeneous or heterogeneous liquid mixtures. • Parts of a mixture are separated because they have different boiling points

11. Separation of a mixture Chromatography Description: Many types of mixtures can be separated by passing the mixture through a porous substance. For example, the ink pigments that are mixed together to make black ink can be separated by spotting the ink on a piece of filter paper and inserting the paper into a beaker of water. • Mixtures are separated because the parts of a mixture move at different speeds through a porous substance.

12. Summary: The Organization of Matter