Chemists 6:45

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

• substance that cannot be broken down into simpler substances.
• fixed comp b/c 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

SYMBOLS FOR ELEMENTS
• 1813 - Jöns Berzelius
(Swedish chemist) suggested symbols
• 1 or 2 letters with 1 st letter always CAPITALIZED
• If 2 letters, 2 nd letter not cap
• Some Latin name of elements
–Gold is Au (aurum)
–Lead is Pb (plumbum)

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

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

Contents of Two Cans of Mixed Nuts
Type of Nut
Peanut
Mass in
Brand A
152.39 g
Mass in
Brand B
191.96 g
Almond 47.02 g 31.18 g
Brazil Nut they different?
57.88 g 19.60 g
1. How are the two brands of mixed nuts alike? How are
Cashew 46.20 g 73.78 g
Hazelnut
Explain.
19.90 g 16.90 g
3. Do the contents of each can meet the FDA regulations?
Pecan 21.40 g 16.90 g
4. On the Brand A label, the nuts are listed in this order: peanuts, Brazil nuts, almonds, cashews, pecans, and hazelnuts. What do you think determines the order?

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

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
Matter Concept map
– Milk, shaving cream, smoke, fog

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 pt – solid to liquid
•Boiling pt – liquid to gas
•These characteristics can be used to separate substances out of
Substances mixtures
Substance Melting point Boiling point
Hydrogen -259.3
°C
Nitrogen -210.0
°C
Ammonia -77.7
°C
Octane (in -56.8
°C
-252.9
°C
-195.8
°C
-33.3
°C
125.6
°C
On p.47

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

SECTION 2.3

OBSERVING CHEMICAL
PROPERTIES
•Candle burns causes hydrogen 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

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 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
•When matter undergoes
, comp of matter changes
•When matter undergoes
, comp remains same