Chem-Phys, Chapter 15 Page 1 Chapter 15 – Classification of Matter

Chem-Phys, Chapter 15 Page 2 Pure Substances A pure substance is a type of matter with a fixed composition. Examples: water, salt, sugar An element is a substance in which all atoms have the same identity. Examples: gold, oxygen, aluminum About 90 elements occur naturally, another 20 have been made by man.

Chem-Phys, Chapter 15 Page 3 Compounds A compound is a substance in which the atoms of two or more elements are combined in a fixed proportion. Examples: –Salt: ALWAYS 60.7% chlorine and 39.3% sodium –Water: ALWAYS88.8% Oxygen 11.2% Hydrogen

Chem-Phys, Chapter 15 Page 4 Mixtures A mixture is a material made up of two or more substances that can be easily separated by physical means. There are two kinds of mixtures: –A heterogeneous mixture is a mixture in which different materials can be distinguished easily. –A homogeneous mixture contains two or more gaseous, liquid, or solid substances blended evenly throughout.

Chem-Phys, Chapter 15 Page 5 Examples of Mixtures Examples of Heterogeneous Mixtures: –A bag of m&m’s. –A mixture of sand and iron filings. –Concrete Examples of Homogeneous Mixtures: –Coke (before the top is taken off) –Gasoline –Air –Plastic

Chem-Phys, Chapter 15 Page 6 Solutions A solution is a homogeneous mixture of particles so small that they cannot be seen with a microscope and will never settle to the bottom of the container.

Chem-Phys, Chapter 15 Page 7 Colloids A colloid is a type of mixture with particles that are larger than those in solutions but not heavy enough to settle out. Examples: –Milk (droplets of fat seen under a microscope) –Fog –Smoke

Chem-Phys, Chapter 15 Page 8 Detecting Colloids When light passes through a colloid, a small portion of the light is scattered by the particles in the colloid. The scattering of light by a colloid is called the Tyndall effect. Example: –Turn on bright lights in fog

Chem-Phys, Chapter 15 Page 9 Suspensions A suspension is a heterogeneous mixture containing a liquid in which visible particles settle. Examples: –Mississippi River water has silt which will settle out. –Some paint has particles of pigment which will settle out. Stirring prevents a suspension from settling.

Chem-Phys, Chapter 15 Page 10 Solutions, Colloids, Suspensions DescriptionSolutionColloidsSuspensions Settle upon standing? No Yes Separate using filter paper? No Yes Particle size 0.1 to 1 nm1-100 nm > 100 nm Scatter Light? NoYes

Chem-Phys, Chapter 15 Page 11 Chapter 15, Section 1 Review 1.Define substance. 2.Define mixture. 3.What is an element? 4.What is a compound? 5.Compare and contrast: Solutions Colloids Suspensions

Chem-Phys, Chapter 15 Page 12 Physical Properties A physical property is any characteristic of a material that you can observe without changing the identity of the substances that make up the material. Examples: –Melting point- Height –Boiling point- Stretchiness –Color- Temperature –Weight- Volume

Chem-Phys, Chapter 15 Page 13 Physical Properties Some physical properties can be determined by appearance: –Color –Physical state Some physical properties can be determined by how something behaves: –A paperclip conducts electricity –A pin is attracted by a magnet –Gold can be pounded into a very thin sheet

Chem-Phys, Chapter 15 Page 14 Using Physical Properties to Separate Separating by size: A mixture of poppy seeds and sunflower seeds can be separated by using a sieve. Separating with magnetism: A mixture of sand and iron filings can be separated with a magnet.

Chem-Phys, Chapter 15 Page 15 Physical Change A change in size, shape, or state of matter is a physical change. In a physical change, no new substances are formed. Examples: –Ice melts into water –Heating a iron rod until it is white hot –Water vapor condenses to make rain

Chem-Phys, Chapter 15 Page 16 Using Physical Change to Separate Sea water can be vaporized and condensed to make pure water without salts or microorganisms. Distillation is the process for separating substances in a mixture by evaporating a liquid and re-condensing its vapor.

Chem-Phys, Chapter 15 Page 17 Chemical Properties A chemical property is a characteristic of a substance that indicates whether it can undergo a certain chemical change. Examples: –Will it burn? A match – yes. Iron nail – no. –React with water? A match – no. Iron nail – yes (rust).

Chem-Phys, Chapter 15 Page 18 Evidence of a Chemical Change Evolution of a Gas (Bubbles, Odor) Formation of a Precipitate (Formation of Cloudiness in a Clear Solution, Solids Collecting at the Bottom or Top) Release of Energy (Heat, Light) Color Change

Chem-Phys, Chapter 15 Page 19 Using Chemical Change to Separate Chemical change can be used to separate: Silver tarnish (black silver sulfide) and be reacted with baking soda and aluminum foil. The resulting reaction releases silver metal and removes the sulfur.

Chem-Phys, Chapter 15 Page 20 Weathering: Chemical or Physical Change? Physical change: When water freezes in cracks and breaks larger rocks into smaller rocks, that is a physical change. Chemical change: Slightly acid water will dissolve the calcium carbonate in limestone. This is a chemical change.

Chem-Phys, Chapter 15 Page 21 Conservation of Mass The law of conservation of mass states that the mass of all substances that are present before a chemical changes equals the mass of all the substances that remain after the change.

Chem-Phys, Chapter 15 Page 22 Law of Conservation of Mass Example If 18 grams of hydrogen react completely with 633 grams of chlorine to make hydrogen chloride, how many grams of hydrogen chloride are formed? Answer: 18 g g = 651 grams of HCl

Chem-Phys, Chapter 15 Page 23 Chapter 15, Section 2 Review 1.How do you identify a substance using physical properties? 2.Compare and contrast physical and chemical changes. 3.Identify chemical changes. 4.What is the law of conservation of mass? How does it apply to chemical changes?