Section 2: Properties of Matter

Warm-up: Panning for gold was a common technique used to separate gold from sand and gravel. What properties of gold allow it to be easily separated from sand and gravel?

Learning Goals Identify substances using physical properties. Compare and contrast physical and chemical changes. Identify chemical changes. Define the law of conservation of mass.

Physical Properties Physical Property: any characteristic of a material that you can observe without changing its identity. Examples: color, shape, size, density, melting point, boiling point

Physical Properties

Physical Changes Physical Change: a change in size, shape, or state of matter. The identity of the material stays the same!!! Examples:

Physical Change cutting Separating mixtures breaking boiling tearing melting

Physical Change Liquid water freezes into ice cubes It’s STILL WATER!!! Rain in a forest turns the dirt into mud It’s STILL DIRT(just wet)!!!! A piece of paper is torn into strips It’s still paper!

Physical Change When a substance changes phase (like when water freezes or boils), it undergoes a physical change!

Separation The best ways to separate substances depends on their physical properties.

Separation Filtration separates substances by size. Magnets can be used to separate magnetic substances from non-magnetic materials.

Separation Many areas that lie close to the sea obtain drinking water by separating it from the salt. The sea water is boiled and the steam is collected. Salt will not boil with the water, it has a much higher boiling point.

Separation Distillation: the process of separating substances in a mixture by evaporating a liquid and collecting the steam. The steam is then cooled down to form a liquid again.

Chemical Properties Chemical Property: a characteristic of a substance that can only be measured by changing the identity of a substance. Examples: flammability, reacts with acid

Chemical Change Chemical change: a change of one substance into another. All chemical reactions are chemical changes.

gas released (often with an odor) energy change (light, heat, …) Chemical Change Four good indicators of a chemical change: color change gas released (often with an odor) energy change (light, heat, …) solid formed

Conservation of Mass Burning a log is an example of a… Chemical change! The log seems to disappear, and you are only left with ash. What happened to the rest of it?

Conservation of Mass The log undergoes chemical changes and releases carbon dioxide, water, and smoke. It doesn’t just disappear, it all goes somewhere.

Conservation of Mass Law of Conservation of Mass: the mass of all substances present before a chemical change is equal to the mass of all of the products after a change.

Check-in: Explain why evaporation of water is a physical change and not a chemical change.