Pure Substances Mixtures

Everything that has mass and volume is called matter.

Fixed composition Cannot be separated into simpler substances by physical methods (physical changes) Can only be changed in identity and properties by chemical methods Properties do not vary

Compounds Can be decomposed into simpler substances by chemical changes, always in a definite ratio Elements Cannot be decomposed into simpler substances by chemical changes

Variable composition Components retain their characteristic properties May be separated into pure substances by physical methods Mixtures of different compositions may have widely different properties

Homogenous mixtures look the same throughout but can be separated by physical means (dissolution, centrifuge, chromatography, osmosis etc.). Examples: milk, yogurt

Have the same composition throughout Components are indistinguishable Examples: alloys, milk, pop, air.

Heterogeneous mixtures are composed of large pieces that are easily separated by physical means (ie. density, polarity, metallic properties).

Do not have same composition throughout Components are distinguishable Examples: fruit salad, vegetable soup, etc.

Classification of Matter Solutions are homogeneous mixtures

Liquids MaterialDensity (gm cm -3 ) Water at 4 C Water at 20 C0.998 Gasoline0.70 Mercury13.6 Milk1.03 Solids MaterialDensity (gm cm -3 ) Magnesium1.7 Aluminum2.7 Copper Gold19.3 Iron7.8 Lead11.3 Platinum21.4 Uranium18.7 Osmium22.5 Ice at 0 C0.92 Gases at STP MaterialDensity (gm cm -3 ) Air Carbon dioxide Carbon monoxide Hydrogen Helium Nitrogen