Chemistry – Chapter 3 Matter – Properties and Changes

Properties of Matter Substance – matter that has uniform and unchanging composition Examples: salt, water Physical properties of matter Physical property – characteristic that can be observed or measured w/o changing the composition Examples: density, color, odor, taste, etc. Table 3-1 Extensive property – dependent upon amount of substance present Examples: length, volume Intensive property – independent of amount Example: density

During gold rush, miners relied on gold’s density to separate gold flakes from sand Chemical property – ability of a substance to combine with or change into one or more other substances Example: rust formation when iron combines with oxygen States of matter – can be distinguished by the way it fills a container Solid – definite shape and volume Liquid – flows, definite volume, takes shape of container Gas – flows, conforms to shape of container, fills entire container Vapor – gaseous STATE of a substance normally solid or liquid at room temp.

Changes in Matter Physical change – alter substance w/o changing composition Ex: crumpling paper, melting, boiling Phase change – temp. and/or pressure change Chemical change – involves one or more substances changing into new substances Reactants – starting substances Products – new substances formed

Making wine Crushing grapes – physical change Fermentation of juice, sugars, etc. – chemical change Conservation of mass Law of conservation of mass – mass is neither created nor destroyed during a chemical reaction Mass reactants = Mass products

Mixtures of Matter Mixture – combination of 2 or more substances in which each retains its individual chemical properties Heterogeneous – does not blend smoothly throughout Ex: chocolate chip cookie dough Homogeneous – constant composition throughout (solutions) All phases Steel – solid-solid solution called an alloy

Separating mixtures Filtration – technique using porous barrier to separate solid from liquid Distillation – technique based on differences in the boiling points of substances involved Mixture is heated until substance with lowest BP boils to a vapor; vapor is collected and condensed Crystallization – technique results in formation of pure solid particles from a solution Chromatography – technique that separates components of a mixture (mobile phase) based on tendency of each to travel across surface of another material (stationary phase)

Elements and Compounds Element – pure substance that can’t be separated into simpler substances by physical or chemical means 91 occur naturally Not equally abundant Hydrogen – 75% of universe Oxygen and silicon – 75% of earth’s crust Oxygen, carbon, hydrogen – 90% of body Periodic Table Mendeleev developed first version Rows – periods Columns – groups Similar properties

Compound – combination of 2 or more different elements that are combined chemically Examples: water, salt, sugar, aspirin Those that occur naturally are more stable than the individual component elements Electrolysis – chemical change of water into hydrogen and oxygen Sodium chloride (salt) – white, unreactive solid that flavors food Sodium – highly reactive element that fizzes and burns when added to water Chlorine – poisonous, pale green gas

Law of Definite Proportions – a compound is always composed of the same elements in the same proportion by mass (regardless of the amount) Mass of compound is equal to the sum of the masses of the elements that make up the compound Percent by mass – ratio of the mass of each element to the total mass of the compound % by mass = element mass/compound mass X 100

Law of Multiple Proportions – when different compounds are formed by combination of the same elements, different masses of 1 element combine with same relative mass of the other element in a ratio Water H 2 OHydrogen Peroxide H 2 O 2 Mass of oxygen in hydrogen peroxide to mass of oxygen in water is 2:1

Chemistry and Society Fossil fuel burning contributes to significant increase in CO 2 Global warming Producing cement – major source of CO 2 Mixture of limestone and sand placed in kiln and heated, causing chemical and physical property changes CO 2 released 2 ways Limestone changes to lime and CO 2 when heated Electrical energy used to heat kiln is supplied by power plants that burn fossil fuels

Flyash –replacement for cement Waste product that accumulates in smokestacks of power plants when ground coal is burned Advantages Reduce flyash dumped in landfills Reduce CO 2 emissions Produces better concrete Using hazardous waste as fuel in cement kilns