dr. childs fall, 2005 science laboratory matter and changes in matter
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MatterMatter is everything that we see and
many of the things we don’t see (as air). By definition matter has mass and occupies space.
Matter is classified into two major categories:- Pure substances - Mixtures
Pure silver
Brass(mixture of copper & zinc)
Matter
Matter can be changed. These changes may involve physical changes in which the composition of the matter is not changed or chemical changes in which the composition is changed.
Ice melting
Candle burning
Pure SubstancesPure substances:
- contain the same type of particles throughout.- have a definite composition.- may be either elements or compounds-
sodiumNa
sodium chlorideNaCl
chlorineCl
Elements & Compounds
• An element is a pure substance that cannot be broken into anther substance (by ordinary chemical means). Composed of only a single type of atom.
• A compound is a pure substance composed by two or more elements
How about some examples?
• Many things are made of elements. For example, aluminum is used for foil and for building cars and trailers.
Elements
Note: If its on the periodic table its an element!
Compounds
Compounds are formed when two or more atoms of two or more elements combine chemically (bonding!).
- fixed ratio of elements with a definite formula - separation into elements requires chemical procedures
Water H2O
Note: Compounds are NOT on the periodic table.
Compounds
table saltNaCl
table sugarC6H12O6
Carbon dioxideCO2
Nitrous oxideN2O
rustFe2O3 Epsom salts
MgSO4
Sodium hydroxideNaOH
MixturesMixtures are materials made up of two or more pure substances.
Mixtures can be separated by physical means based on physical properties:
evaporation filtrationfloating magnets
Mixtures may be eitherhomogeneous (solutions)heterogeneous
MixturesHomogeneous mixture of metal are “alloys”. Alloys include brass, steel, and white gold.
Homogeneous mixtures in which one substance is dissolved in another is a “solution”. Solutions include coffee, IV fluids, and fog.
Examples:
Sea water water and saltCoffee coffee, sugar, creamBlood red cells, white cells, plasmaAir nitrogen, oxygen, CO2
Brass copper, zincWhite gold gold, silver, platinum
Homogeneous Mixtures
Examples:
raisin bran cereal with raisinschocolate chip cookietossed salad lettuce, tomatoes, carrotspizza pizza with meat, cheesegranite feldspar, micaItalian dressing oil, water, spice
Heterogeneous Mixtures
Raisin Bran
Granite
MarbleMuddy water
Tossed salad
Heterogeneous MixturesItalian dressing
Chocolate Chipcookie
Physical & Chemical Properties
Be sure to know the difference between:
- Physical properties &chemical properties
- Physical changes &chemical changes
Physical Properties
Physical properties can be observed without a chemical reaction.
Examples:
color: water is clear, table salt is whitedensity: aluminum has a density of 2.7 g/cm3
state: oxygen is a gas at room temperature
magnetism: iron is attracted to magnet
texture: gold is shiny
Physical ChangesIn a physical change substances are not altered
chemically, including:
state changes solid liquidliquid gas
mixing or separatingadding sugar to coffee evaporating sea water for salttearing paper
Physical ChangesState Changes
liquid solid “freezing” water to ice
liquid gas “evaporation” water to steamgasoline to vapor
solid gas “sublimation” dry ice to CO2
freezing evaporationsublimation
Physical ChangesState Changes
solid liquid “melting” ice to waterice cream melting
gas liquid “condensation” ice to water
melting
condensation
Physical Changes
Planing wood
Physical changes may involve changing shape but not composition;
Sawing wood
Breaking glass
Chemical Properties
Chemical properties: The properties of an element or compound
in a chemical reaction
Examples:
gasoline is flammable
water can be separated by electrolysis
neon is inert
Chemical changesChemical reactions:
- yield new substances
- usually cannot be easily reversed
- may either require or release energy (light, heat, etc.)
Sugars in wood may be split by burning. Combustion yields new substances: CO2 and water and heat and light energy.
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