Pure substances = matter that has the same composition throughout; any piece of a pure substance will have the same properties

Transcription

1 Ch. 2 - Properties of Matter Composition A putting together; combining of parts into a whole. Substances are either pure or mixtures. Pure substances = matter that has the same composition throughout; any piece of a pure substance will have the same properties Two types of pure substances: 1. Element Can't be broken down into simpler substances. The smallest unit of an element is an atom. Elements contain only 1 type of atom EX: aluminum foil, pencil lead (carbon), Oxygen gas, gold 1

2 2. Compounds a substance that is made from 2 or more simpler substances, always in a fixed ratio, and can be broken down into these substances. The properties of a compound are often very different than the properties of its components. EX: Oxygen and hydrogen are gases, yet produce liquid water (H 2 0) when combined. Mixtures = Combination of different substances; the ratio of these substances can vary; the properties will vary based on the distribution of the components. Two types of mixtures: 1. Heterogeneous mixture the parts of the mixture are noticeably different from each other. (hetero = different, genus = kind) EX: sand, salsa, Chex mix 2

3 2. Homogeneous mixture substances are so evenly distributed that the mixture appears the same throughout - appears to only contain one substance. EX: Pepsi, swimming pool water, stainless steel and other alloys 1. Solutions a homogeneous mixtures where one substance is completely dissolved in another. These: ~don't separate into distinct layers over time, ~ can't be filtered, and don't scatter light. ~Has the smallest particles. Ex: salt water, Kool-Aid, tap water Some substances are more difficult to classify! The size of the particles in a mixture can affect the properties of the mixtures. We classify these mixtures based on the size of the largest particles: 3

4 2. Suspensions a heterogeneous mixtures that: ~separates into layers over time, ~can be filtered and ~can scatter light (which is why they appear cloudy). ~Has the largest particles. Ex: dust in air, sand in water 3. Colloids contains medium sized-particles that: ~do not separate into layers, ~can't be filtered and ~DOES scatter light. Ex: Fog in air, homogenized milk particle size seperate into layers can be filtered scatters light Solution Suspension Colloid 4

5 Section Physical Properties Physical property = a characteristic of a material that can be measured or observed without changing the composition of the material. Types of physical properties: 1. viscosity = resistance of a liquid to flowing. As a substance is heated, what usually happens to viscosity? 2. conductivity = ability to allow heat to flow. Metals are usually good heat conductors (as well as good electrical conductors), while wood is a poor conductor 3. malleability = ability of a metal to be hammered without shattering. Most metals are malleable (whereas glass is not!) 4. hardness = ability to scratch another substance. Diamonds are the hardest known material. 5

6 5. melting and boiling points = melting point is when a substance changes from solid to liquid; boiling point is when a substance changes from liquid to gas. 6. Density = ratio of the mass of a substance to its volume. Can be used to determine the purity of a substance (its how nuggets were determined to be gold back during the gold rush!) Physical properties can be used to: 1. Identify a material decide the properties to test, test the unknown, compare results to known results (this is how much crime scene evidence is identified!) 2. Choose a material for a specific purpose 3. To separate the substances in a mixture Filtration = separates materials based on the size of their particles Distillation = separates substances of a solution based on their boiling points. 6

7 If you were stranded on a boat, how could you use physical properties to separate the materials in salt water to obtain fresh drinking water? Where do we get our drinking water from? Section Chemical Properties Chemical property = can be observed only when the substances in a sample of matter are changing into different substances. Types of chemical properties: 1. Flammability material's ability to burn in the presence of oxygen EX: gasoline, wax, paper 2. Reactivity how readily a substance combines chemically with other substances. Analyze the diagram on p and write a short explanation of the steps involved in purifying drinking water. EX: oxygen is highly reactive, while nitrogen is not 7

8 What substance reacts with oxygen to form rust? What would be a way to prevent iron ships, that often store seawater in the bottom of their decks to help maintain balance, from rusting on the inside? Chemical changes a substance reacts and forms one or more new substances. Signs of chemical changes include: 1. Change in color = silver tarnishing, copper "greening" 2. Production of gas = bubbles form; cake rises, vinegar + baking soda = gas production 3. Formation of a precipitate = a solid forms and separates from a liquid mixture; milk curdling 8

9 When matter undergoes a chemical change, the composition of the matter changes. When matter undergoes a physical change, the composition of the matter remains the same. 9