chapter 15 classification of matter. pure substances materials are made of a pure substance or a...
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Chapter 15
Classification of Matter
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Pure Substances• Materials are made of a pure substance or a
mixture of substances• A pure substance, or substance, is a type of
matter with a fixed composition• A substance can either be an element or a
compound ex. Helium, Water, Salt
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Elements• All substances are built from atoms• If all atoms in a substance have the same
identity, the substance is an element• Ex. Copper, gold, silver
All of the elements are found on the Periodic Table
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Compounds• Two or more elements can combine to form a
compound• A compound is a substance in which the atoms of
two or more elements are combined in a fixed proportionEx. Table Salt
- Compounds have properties different from the elements that compose them
- Definite Ratio- Can only be decomposed into elements by
chemical rxns. (can’t physically separate them)
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Mixtures• A mixture is a material made up of two or more
substances that can be easily separated by physical means• Components retain their own identifying
properties• No definite composition• Can be separated by dissolving, filtering,
evaporating, magnetics, screening, etc.• Mixtures can either be heterogeneous or
homogeneous
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Heterogeneous mixtures
• A heterogeneous mixture is a mixture where different materials can be distinguished easily
• Some are easily seen while others are not• Ex. Pizza
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Homogeneous Mixtures• A homogeneous mixture contains two or
more gaseous, liquid, or solid substances blended evenly throughout• Components can’t be seen with the naked
eyeEx. Soft Drink in a bottle – contains water, sugar, flavoring, coloring, CO2 gas
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Solutions• Solution - A homogeneous mixture in which
the components are close to the size of individual particles of the substance and are too tiny to be seen with a microscope and will never settle to the bottom of a container
• Solutions remain constantly and uniformly mixed
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Mixtures can occur between and among all phases of matter• Gas/gas (air)• Gas/liquid (oxygen in water)• Liquid/liquid (alcohol in water)• Liquid/solid – (sugar in water)• Solid/solid – (alloy such as steel)
Ex. The addition of 10-30% chromium creates stainless steel
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Physical Properties• A physical property of a substance is any
characteristic of a material that you can observe without changing the identity of the substances that make up the material• Physical properties can be observed directly
of measured with a tool
• Examples of physical properties include boiling point, color, shape, size
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Boiling/Freezing/Melting Points
• Boiling/Melting/Freezing points refer not to the phase change itself, but to a measurement: the temperature at which these changes occur
• Physical properties because the composition of a substance doesn’t change during phase change or when one measures temperature to determine these points
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Density• Density is the mass of a substance per unit volume• The density of a particular substance (under
constant conditions) is always the same, regardless of sample size
• The composition of a substance doesn’t change when one measures mass and volume to find density -> physical property
Density = mass volume
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Solubility• Solubility – the maximum amount of a solute
(substance being dissolved) that can dissolve in a given volume of solvent (the dissolving medium) at a particular temperature and pressure
• The components of solutions do not chemically combine to form a new substance, therefore solutions are composed of two substances which each retain their own properties -> physical property
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Viscosity• Viscosity is a measure of a material’s
resistance to flow• High viscosity fluids take longer to pour than
low-viscosity fluidsThe composition of a fluid doesn’t change when it is poured -> physical property
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Electrical Conductivity• A solid is either an electrical conductor or
insulator based on its ability to complete an electric circuit
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Physical Changes Review
Any observations/measurement made WITHOUT changing the composition of the matter
ColorTextureDensityOdorSolubilityMelting/boiling point (Any Phase Change)
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Physical Change• A change in size, shape, state• Identity of the element/compound does not
change• Change in Shape/Size
• Aluminum Foil cut in half• Chewing your food
• Change in State• Rubbing alcohol evaporates in your hand• Juice box freezes in freezer
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Signs of a Physical Change
Any phase change
Change in energy of the particles
What you started off with is what you end up with chemically
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Chemical Properties• A chemical property is a characteristic of a
substance that indicates whether it can undergo a change that will alter the composition of the substanceA change of one substance to another
• Ex. The capacity to oxidizeThe capacity to corrodeCombustibility
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Chemical Changes• Substance(s) present at the beginning of the
reaction are changed into something new.• You BREAK or MAKE bonds!!• The change can’t be undone
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Examples• Gasoline is ignited/burns• Car rusts• Milk goes sour• Bread -> toast• Food digesting in your stomach and small
intestine
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Signs of Chemical Change
• Bubbles appear• Something is burning• A precipitate forms (solid appears)• Color Change• Temperature changes• Smell
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The Capacity to Oxidize• A substance combines with oxygen to form
a new substance with new properties• The new substance formed is a combination
of the atoms of the original substance and oxygen
• Properties of a substance change during the process of oxidation
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Combustibility• Combustion is a special type of oxidation• When combustion occurs, a substance
combines with oxygen to form a new substance with new properties in a process that releases heat and light
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The Capacity to Corrode
• Corrosion – the process by which metals naturally combine with oxygen, sulfur, or other nonmetals
• When corrosion occurs, the new substance that is formed is a combination of a metal and a nonmetal
• The properties of a substance change during this process
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Conservation of Mass• The mass of all substances present before a
chemical change equals the mass of all the substances that remain after the change (this will be more important later)• Ex. A burning log, even though ashes are left
and weigh less, if you could collect all the gases lost during the burning and measure their masses too, mass would be conserved