3. Review of Pure Substances There are two types of pure substances: 1. Elements Elements are composed of one kind of atom. Examples are on the periodic table. 2. Compounds Compounds are composed of two or more elements chemically combined in a fixed ratio When the atoms of the elements combine chemically they form molecules of a compound Examples: H 2 O, NaCl, C 2 H 5 OH, Fe 2 O 3

4. Examples of atoms of elements forming molecules of compounds A. B. A.One carbon atom and one oxygen atom make one molecule of carbon monoxide B. One carbon atom and two oxygen atoms make one molecule of carbon dioxide

5. Examination of Mixtures 1. Solutions 2. Suspensions 3. Colloids There are three types of mixtures: Uniformly mixed, homogeneous mixtures of two or more pure substances Heterogeneous mixtures of two or more pure substances in which the substances are visible with the naked eye Heterogeneous mixtures of two or more pure substances in which the particles of the substances are too small to be seen with the naked eye, but separate out over time.

6. Examples of Solutions: An aqueous solution of copper sulfate (Water and copper sulfate) An aqueous solution of potassium dichromate (Water and potassium dichromate) The Metallic alloy - Brass ( a mixture of copper and zinc) Other examples: air (mixture of gases) water and ethyl alcohol water and oxygen gas

7. All solutions have a solute and a solvent For example: If 5.0 grams of table salt (solute) is completely dissolved in 100 mL of water (solvent) The concentration of the aqueous salt solution = 5.0 g/100 mL Solutions always have a concentration The concentration can be expressed as a solute to solvent ratio When a solid is dissolved in a liquid, the solid is termed the solute, the liquid the solvent. When one liquid is dissolved in a second liquid, the liquid present in the smaller amount is usually called the solute. (the same for a gas in a gas)

8. Depending on the concentration, liquid solutions can be: 1.Unsaturated In an unsaturated solution more solute may be dissolved in the solvent at a given temperature 2. Saturated In a saturated solution no more solute can be dissolved in the solvent at a given temperature 3. Supersaturated In a supersaturated solution more than the predicted normal maximum amount of solute has been dissolved. A supersaturated solution can be created when a liquid solution is heated and then slowly cooled.

9. Liquid solutions can be separated physically by using evaporation A solution heated in an evaporation dish

10. Examples of heterogeneous mixtures and suspensions (note: suspensions have a liquid or gas component) oil and vinegar - a suspension (if shaken) sand and water - a suspension (if shaken) iron, sulfur and salt - a solid heterogeneous mixture Heterogeneous Mixtures - Suspensions A rock is formed from a number of substances mixed heterogeneously Certain rocks are solid heterogeneous mixtures

11. Suspensions in liquids have two or more visibly obvious components, in which, the components can be separated physically by filtration or decantation FiltrationDecantation

12. Heterogeneous Mixtures - Colloids milkshaving cream fog marshmellows jellopearls mustard mayonnaise The particles in colloids are in between the size of those in solutions and those in suspensions. Colloids look homogeneous, but are not. Liquid colloids will separate out slowly over time. Examples of Colloids:

13. Colloids are often opaque, which means, you can not see through them. But sometimes liquid colloids can be clear and can be confused or mistaken for a solution! If one is not sure, there is a way to find out. By using something called The Tyndall Effect

14. The Tyndall Effect is used with gas and liquid mixtures. It is a method by which a clear solution and a clear colloid Can be identified. Light is passed through the unknown liquid or gas mixture. Since Light bounces off of particles, the greater the particle size the more light will be seen. If the reflected light is visible to the naked eye, then the mixture is considered to be a colloid

15. colloidsolution (or a pure liquid) The Tyndall Effect The laser light travels through the solution with little or no reflection of light, while the beam is very obvious in the colloid. light source http://www.silver-lightning.com/tyndall/

16. solution solution suspension suspension colloid colloid homogeneousheterogeneousheterogeneous Very tiny particles do not settle out Larger particles settle out quite quickly Particles larger than those in a solution will eventually settle out No Tyndall effect Tyndall effect No separation by filtration or decantation Separation by filtration or decantation No separation by filtration or decantation A Comparison of Liquid Mixtures

17. A Comparison of Mixtures and Compounds Mixture Mixture Compound Compound 1. Components may be in any proportion Components are in fixed proportions 2. Individual components retain their own properties Individual components lose their identities. A new set of properties result 3. Components may be separated by physical means Components may only be separated by chemical means 4. When mixed there is little, if any evidence of a chemical change. When combined there is evidence of a chemical change (heat, light, gas production, precipitate). 5. It is a physical combination of pure substances It is a chemical union of atoms of elements, to form molecules of compounds

18. Identify the following as: element, compound, solution, suspension, colloid peanut butter nitrogen ethanol cement oil and water salt water lithium steel ketchup whipped cream air water carbon milk carbon dioxide sand and ethanolwater and vinegar