CHAPTER 2PROPERTIES OF MATTER

PURE SUBSTANCESPURE 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

COMPOUNDSCOMPOUNDS• Substance made of 2 or more

simpler substances • Can be broken down into simpler

substances (elements or other compounds)

• Always joined in fixed proportion–H20 – 1 drop or 1 gallon, always 2

parts hydrogen for every 1 part oxygen

MIXTURESMIXTURES• 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 MIXTURESHETEROGENEOUS MIXTURES

•parts of mixture noticeably different from one another

– Sand, trail mix, Lucky Charms, Italian salad dressing

HOMOGENEOUS MIXTURESHOMOGENEOUS 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, SOLUTIONS, SUSPENSIONS, AND COLLOIDSAND COLLOIDS

•3 major classifications of mixtures:

•Based on size of largest particles:

SOLUTIONSSOLUTIONS• 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

SUSPENSIONSSUSPENSIONS• 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

COLLOIDSCOLLOIDS

• 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 H2O and sea H2O 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 H2O

PHYSICAL V.S. CHEMICAL CHANGE

•When matter undergoes

chemical changechemical change, comp of matter changes

•When matter undergoes physical physical changechange, comp remains same