What you’ve learned so far. (Pure) Substances v. Mixtures. You have learned how to distinguish between substances based upon the composition. You can now categorize substances into two classifications, either pure substances or mixtures. Physical Properties. You now know what is a physical property of a substance. You also know over 10 examples of these. You can use physical properties to identify an unknown substance, to choose a substance for a purpose, or to separate substances.

Review, Physical Properties Using Physical Properties to Identify Materials Physical properties are used to identify a material, to choose a material for a specific purpose, or to separate the substances in a mixture. Using Properties to choose materials Hardness, Viscosity, Malleability, Density, Boiling point and melting point, Conductivity, Color, Texture, Temperature Using properties to separate mixtures Filtration – separation based on size of particles Distillation – separates based on boiling point

Physical Properties Questions – To Discuss in Class Name 2 processes that are used to separate mixtures. When you describe a mixture as having high viscosity do you mean it is thick or runny? Explain why sharpening a pencil is an example of a physical change? What physical property allows a mixture to be separated by distillation?

Section 3: Chemical Properties Objectives: Describe the chemical properties of matter. Identify and illustrate the clues that indicate a chemical change is taking place. Distinguish chemical changes from physical changes.

Chemical Properties Vocabulary Chemical property Flammability Reactivity Chemical change Precipitate

Observing Chemical Properties Chemical properties can be observed only when the substances in a sample of matter are changing into different substances. Chemical property: any characteristic that can produce a change in the composition of matter What is composition again? What it’s made of. Matter is made of atoms, molecules, mixtures, etc

Observing Chemical Properties Are these chemical changes?

Examples of Chemical Properties Flammability- ability of a substance to burn in the presence of oxygen. Note that not everything is flammable &… There isn’t oxygen everywhere. So how do rockets burn in space? Any suggestions?... They bring their own oxygen!

Examples of Chemical Properties Reactivity- how easily a substance combines chemically with another substance Some matter reacts more than others. Examples: Metals like Lithium, Sodium, and Potassium rarely occur by themselves in nature. Strong acids and bases are reactive. Oxygen is highly reactive as well. Oxidation: A chemical process that results in the combination of a substance with oxygen. Oxygen is found in the air and easily reacts with other substances. For instance Iron Oxide which is rust Nitrogen, on the other hand is found in the air and has low reactivity

Chemical Properties Recognizing Chemical Changes A chemical change occurs when a substance reacts and forms one or more new substances. 3 common clues that a chemical change has occurred. Change in color. Production of a gas. Formation of a precipitate.

Change in Color Example: Steel (made of iron) rusts in a humid or moist environment. We know a chemical change has happened because there is a change in color! The chemical property, reactivity, is responsible.

Formation of a Gas Baking soda releases a gas when it is heated causing cakes to rise.

Formation of a Precipitate: Precipitate: a solid that forms and separates from a mixture. Silver nitrate added to potassium chloride produces the precipitate, silver chloride, the white cloud.

Chemical Properties Recognizing Chemical Changes: More examples… A Change in Color – copper roofs react with oxygen in the atmosphere and change from copper color to green, called patina. Production of a Gas – if we add baking soda to vinegar we get production of a gas. Baking soda is a base, vinegar is an acid (acetic acid). Formation of a Precipitate – Any solid that forms and separates from a liquid mixture is called a precipitate. When lemon juice is added to milk, it curdles.

Finally: Chemical Properties Is a change chemical or physical? In summation, to understand whether or not a change is chemical or physical consider the following: Tell me, how do you know if a change is physical or chemical? When matter undergoes a chemical change, the composition of matter changes. When matter undergoes a physical change, the material may change shape or size but the composition of matter remains the same.

Do you understand the concepts Do you understand the concepts? Identify if the example is a chemical or physical property and describe why. A banana changes color when it ripens. A pencil gets sharpened. Getting your hair cut. Water bubbles when it boils. A nail rusts when it’s left in a bucket of water. Aluminum has a low density. Wood burns in a campfire. Salt dissolves in water. A horseshoe glows red when it is heated. Vinegar bubbles when mixed with baking soda. Hydrogen combines with oxygen to form water. Chemical Physical

Finish… Worksheet 2.3 Tomorrow: Physical/Chemical Properties Lab