Properties of Matter

Objectives  Identify substances using physical properties  Compare and contrast physical and chemical changes  Identify chemical changes  Determine how the law of conservation of mass applies to chemical changes

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 are:  Color  Shape  Size  Density  Melting point  Boiling point

Appearance  A tennis ball can be described by –Its bright color –Its spherical shape –Its hollow center –Its circumference  A soft drink can be described by –The fact that it is a liquid –Its brown color –Its volume

What ways could this be described

Behavior  Some physical properties of materials describe the behavior of a material or substance. –An important property of iron is the fact that it is attracted to magnets –A property of gold is that it can be pounded into sheets 4 millionths of an inch thick –The ability to flow is an important property of liquids

Using special properties to separate  By using a sifter, one can separate materials by size  Prospectors that “pan” for gold are using the fact that gold is usually more dense than the other materials in the stream to separate it out by density  A lot of recycling plants use strong magnets to separate scrap iron from aluminum

Physical change  When you change some of an object’s physical properties, you do not change the identity of the materials that make it up.

Phase changes  When an substance freezes, boils, evaporates or condenses, it undergoes a physical change. –The addition or removal of energy is what causes phase changes. – Color changes often accompany phase changes, but the change of this property does not change the identity of the material

 Even though this molten iron is red, it still has the same characteristics of iron

Using physical change to separate  Distillation is a method used to separate substances in a mixture by evaporating a liquid and recondensing its vapor

Chemical properties and changes  A chemical property is a characteristic of a substance that indicates whether it can undergo a certain chemical change Flammability is an important chemical property for many substances Light sensitivity is another important chemical property

Detecting Chemical Change  The change of one substance into another is a chemical change –Signs of a chemical reaction include  Heat  Cooling  The formation of bubbles  The formation of solids –Some chemical reactions take place slowly (like rusting) while other take place at a much more rapid pace (like the burning of rocket fuel)

Using chemical change to separate  Silver tarnishes in the presence of sulfur compounds in the atmosphere  The pure silver can be separated out from the new compound by adding the tarnished silver to warm water with aluminum foil and baking soda

Weathering – Chemical or Physical change?  The weathering of the Earth’s surface is both a physical and chemical change. –Physical changes include The splitting of rocks by freeze thaw cycles does not change the make up of the rock so therefore it is considered a physical change The cutting through and wearing away of softer rock by the actions of water is also a physical change because the water just gouges away the rock taking with it sand and gravel sized pieces of the larger rock These processes are responsible for the Grand Canyon

–Chemical changes include  The dissolving of rock by slightly acidic water –Limestone easily dissolves in acidic water –When acidic water seeps through limestone and some other minerals, it dissolves some of the material and takes it away. –This process is responsible for the formation caves and the structures found in them

Conservation of mass  By observing a burning log turn to ash, you may be tempted to think that during the chemical change that occurred, some mass was lost.  It was not!!! If you gathered all of the gases that formed, soot that was carried away, and water that evaporated out when the log was hot, you would find that there is exactly the same amount of mass after the log was burned as before the log was burned

Conclusion  What physical properties of a material can use to identify it?  Is melting a solid a chemical or physical change?  When making diner, what chemical changes are occurring?  If I take this Sunday’s Inquirer and start a fire in my fire place to warm me up for the Eagles game, what is going to happen to the mass of the newspaper after it has been burned? Were did the components that made up the newspaper go?