Lesson 12 – Classification of Matter

1. Lesson 12 – Classification of Matter

2. Objectives: -         The student will differentiate between pure substances and mixtures. -         The student will differentiate between elements and compounds. - The student will differentiate between homogenous and heterogeneous mixtures.

4. I.                    Mixtures and Pure Substances a.       Matter can be classified as either a pure substance or a mixture                               i.      A pure substance is matter made up of only one kind of atom or molecule. 1.      Pure substances have specific chemical and physical properties. 2.      They can consist of single elements, or single compounds composed of multiple elements. 3.      Examples a.       Carbon dioxide b.      hydrogen c.       copper

5. ii.      A mixture is a collection of two or more pure substances physically mixed together that cannot be represented by a chemical formula 1.      Chicken soup – liquid, vegetables, chicken, etc. 2. 18 or 14 karat gold – mixture of gold and silver.

6. II.                    Mixtures can be further classified a.       A homogenous mixture is a mixture containing substances that are uniformly distributed throughout. Any which are mixed on the scale of individual particles are solutions. Solutions do not settle if allowed to sit for a time, and the particles that are mixed in are small enough to not scatter light shined through the solution. Another name for a homogenous mixture is a solution. b.      A solution consists of two parts – a solute and a solvent.                             i.      The solute is the component of the mixture which is present in the lesser amount. ii. The solvent is the component of the mixture which is present in the greater amount.

7. c.       Examples of homogenous mixtures/solutions                                 i.      Gasoline                                 ii.      Syrup                                 iii.      Salt water                                 iv.      Sugar in water                                 v.      Air d.      A heterogeneous mixture is a mixture containing substances which are not evenly distributed throughout.                                 i.      heterogeneous mixtures can take many different forms ii. properties in one region of the substance may differ from properties in a different region of the substance

8.                     iii.      A phase is any area of a system that has uniform properties. 1.      Oil and vinegar salad dressing – a 2 phase, heterogeneous mixture 2.      Many plastic products have different phases                      iv.      There is no way to distinguish between homogenous and heterogeneous mixtures which appear to be uniform to the naked eye.                      v.      Heterogeneous mixtures can be separated into colloids and suspentions. 1.      Colloids are heterogeneous mixtures where the particles are large enough to scatter light, but are small enough to remain suspended. Whipped cream and egg white are considered colloids. 2. Suspensions are heterogenous mixtures where the particles are large enough to settle out of the mixture when allowed to sit for a time. Muddy water is an example of a suspention.

9. III.   Pure substances can also be further classified a.       Elements                     i.      Elements are the simplest pure substances. They contain only one kind of atom (not necessarily only one atom)                             ii.      Every element has its own unique set of properties.                             iii.      A small number of elements make up most common substances.                             iv.      There are approximately 118 different elements. v. Elements may consist of single atoms or molecules.

10. 1.      Helium – an element that exists by itself. - He 2.      Nitrogen – an element that is found in pairs – N2 – This is known as a diatomic gas. 3.      Oxygen – found in two allotropic forms a.       O2 – the oxygen we breathe b. O3 – ozone, a poisonous gas

11.                      vi.      Allotropic forms 1.      Some elements, such as oxygen, phosphorous, sulfur, and carbon, exist as allotropes 2.      Allotropes are different molecular forms of an element in the same physical state 3.      Examples a.       oxygen and ozone b. carbon – graphite and diamond, as well as buckminsterfullerine (“buckeyballs”) and buckeytubes.

13. b.       Compounds                       i.      Compounds can be separated into elements 1.      Compounds are pure substances composed of two or more different elements that are chemically combined. 2.      Compounds are created in chemical reactions. 3.      There are several different types of compounds, which will be covered later in this course.                               ii.      Every compound has a unique set of properties 1. Compounds have different properties from the elements which make them up. 2. Examples a. Sodium chloride – table salt, which is an edible solid; Sodium is a corrosive metal, and chlorine is a toxic gas.

14. 3. Compounds can be distinguished from mixtures a.       Mixtures are never made up of only a single compound b. The properties of a mixture reflect the properties of the substances it contains, while the properties of a compound may have nothing to do with the properties of the elements which make it up. c.       Compounds have a definite composition, by mass, of the elements which make them up. Mixtures can vary in proportions. i. Example – CO2 always has one carbon atom for every two oxygen atoms, combined in a group of three. Oil and vinegar salad dressing may have more oil than vinegar, the same amount of each, or any other proportion that is possible.

15. Questions: 1. Compare and contrast pure substances and mixtures. 2. Compare and contrast homogenous and heterogeneous mixtures, including how many phases each may possess. 3. Compare and contrast elements and compounds, including at least two examples of each. 4. Draw a diagram relating the following terms – Homogenous mixture, Compound, Matter, Element, Heterogeneous mixture, Pure Substance, Mixture.