CHAPTER 2 PROPERTIES OF MATTER

PURE SUBSTANCES Matter w/ same composition throughout –Table salt or sugar Every pinch tastes equally salty/sweet 2 categories: –Elements –compounds

ELEMENTS substance that cannot be broken down into simpler substances. fixed comp because it has only 1 type of atom –Cutting copper wire into smaller and smaller pieces until you end up with copper atoms No 2 elements contain same type atom

EXAMPLES OF ELEMENTS At room temp (20°C, or 68°F), most solids, some gases, 2 liquids

COMPOUNDS Substance made of 2 or more simpler substances Can be broken down into simpler substances (elements or other compounds) Always joined in fixed proportion –H 2 0 – 1 drop or 1 gallon, always 2 parts hydrogen for every 1 part oxygen

MIXTURES Similar to cmpds b/c multiple substances Different b/c properties can vary b/c composition NOT fixed –salsa – each bite has different amt of onion, pepper, etc –Pizza – each slice has diff amt toppings

HETEROGENEOUS MIXTURES parts of mixture noticeably different from one another –Sand, trail mix, Lucky Charms, Italian salad dressing

HOMOGENEOUS MIXTURES Substances evenly distributed difficult to distinguish one substance from another Appears to contain only one substance Stainless steel (iron, chromium, and nickel), Kool-Aid, and pool water

SOLUTIONS, SUSPENSIONS, AND COLLOIDS 3 major classifications of mixtures: Based on size of largest particles:

SOLUTIONS small particles dissolved creating a homogeneous mixture –Windshield washer fluid, sweetened tea, Kool-Aid Particles too small to settle out, be trapped by filter, or scatter light

SUSPENSIONS Heterogeneous mixture separates into layers over time –Italian salad dressing, dirt particles in the air, quicksand Large particles can be trapped by filter and scatter light making suspensions cloudy

COLLOIDS Intermediate size particles – larger than solution, smaller than suspension Large enough to scatter light, too small to settle out / filtered –Milk, shaving cream, smoke, fog

PHYSICAL PROPERTIES SECTION 2.2

VISCOSITY resistance to flow High viscosity  slow flow high visc: – honey, lava, motor oil low visc: – water, vinegar, olive oil

CONDUCTIVITY measure of material’s ability to allow flow of heat / electricity Metals  high conductivity – called conductors Wood, rubber, and styrofoam  low conductivity – poor conductors

MALLEABILITY Material’s ability to be hammered w/o shattering Most metals malleable ex. gold, lead, iron

HARDNESS Material’s resistance to be scratched Harder substances “scratch” softer ones Grinding wheels high $ b/c Contains diamond chips

MELTING & BOILING POINTS Melting point – solid to liquid Boiling point – liquid to gas These characteristics can be used to separate substances out of mixtures

DENSITY Tests purity of substances Mass - volume ratio Methanol is fuel burned in some racing motorcycles. Must be 99.65% pure

USING PROPERTIES TO SEPARATE MIXTURES FILTRATION Separating materials based on size of particles brewing coffee iced tea

DISTILLATION When solution can’t be filtered, distillation used Distillation provides fresh water for submarines Fresh H 2 O and sea H 2 O separated b/c differences in boiling pts

RECOGNIZING PHYSICAL CHANGES Physical change – some properties of a material change, but substance remains same Ex. Melting ice cream, cut hair, crumple paper

CHEMICAL PROPERTIES SECTION 2.3

OBSERVING CHEMICAL PROPERTIES Candle burning causes water and carbon from paraffin to turn into carbon dioxide (new substance that was not originally present) Chemical properties observed only when substances are changing into different substances

FLAMMABILITY Burning in presence of OXYGEN Burning substances used as fuel Gasoline coal wood Sometimes not desirable Children’s sleepwear – low flammability Difficult to ignite Burns slowly

REACTIVITY When oxygen from air reacts with iron from car & water from air…..rust forms completely new substance……… Oxygen + water + iron = iron oxide (rust) Nitrogen is less reactive – N gas used in submarine tanks to replace reactive O gas

RECOGNIZING CHEMICAL CHANGES Look for: gas produced heat produced **change in color precipitate (solid) formed **Color change alone can also be a physical change

IS A CHANGE CHEMICAL OR PHYSICAL? Color change as physical change…despite color change, iron is still iron Gas produced as physical change/…water boiling changes phases (liquid to gas) but still H 2 O

PHYSICAL V.S. CHEMICAL CHANGE chemical changeWhen matter undergoes chemical change, comp of matter changes physical changeWhen matter undergoes physical change, comp remains same