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 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 1
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: 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. 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 Ex: dust in air, sand in water Section 2.2 - Physical Properties Physical property = a characteristic of a material that can be measured or observed without changing the composition of the material. 2
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. 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!) 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? 2. Choose a material for a specific purpose read about how sculptures are made on p. 49! 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. Where do we get our drinking water from? Analyze the diagram on p. 52-53 and write a short explanation of the steps involved in purifying drinking water. 3
1. Flammability material's ability to burn in the presence of oxygen Section 2.3 - Chemical Properties EX: gasoline, wax, paper Chemical property = can be observed only when the substances in a sample of matter are changing into different substances. Types of chemical properties: 2. Reactivity how readily a substance combines chemically with other substances. EX: oxygen is highly reactive, while nitrogen is not 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 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. 3. Formation of a precipitate = a solid forms and separates from a liquid mixture; milk curdling 4
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