AP Chemistry
Ch. 1 Section 1.9 Notes
Classification of Matter
Matter
• has mass
• occupies space
• Exists in three states: solid, liquid, and gas
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Solid
rigid shape
fixed volume and shape
very little volume change as temperature and pressure change
properties determined by arrangement of particles
only slightly compressible
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Liquid
definite volume but no specific shape
assumes the shape of its container
fluid
well-defined surface
only slightly compressible
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Gas
no fixed volume or shape
takes on the shape and volume of its container
highly compressible
volume varies according to temperature and pressure
Classification of Matter
• Matter can be classified into mixtures and pure substances.
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Pure Substances
A pure substance is one with constant composition.
The composition of a pure substance is always the same, regardless of its source.
Example: all samples of water contain the same proportions by mass of hydrogen and
oxygen.
Pure substances contain compounds (combinations of elements) or free elements.
Compounds
Substance with a constant composition that can be broken down into elements by chemical
processes.
Example: sodium chloride (NaCl) commonly called table salt
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Elements
Elements are substances that cannot be broken down into simpler substances by chemical or
physical means.
Sodium, chlorine, iron, lead, copper, and aluminum are all common examples of elements.
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Mixtures
Most matter consists of mixtures of pure substances.
Examples: wood, gasoline, wine, soil, and air
Mixtures have variable composition.
Two types: homogeneous and heterogeneous
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Homogeneous Mixtures
visibly indistinguishable parts
same properties throughout
also called solutions
Examples: salt dissolved in water, brass, and air
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Heterogeneous Mixtures
visibly distinguishable parts
consists of two or more regions called phases that differ in properties
Examples: pizza, chicken noodle soup, ice cubes in water
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Separation of Mixtures
Mixtures can be separated into pure substances by physical methods.
1. Distillation: a process that depends on the differences in the volatility (how readily
substances become gases) of the components.
In simple distillation, a mixture is heated in a device and the most volatile component
vaporizes (turns into gas) at the lowest temperature, and the vapor (gas) passes
through a cooled tube (a condenser) where it condenses back into the liquid state.
2. Filtration: used when a mixture consists of a liquid and a solid.
The mixture is poured onto a mesh, such as filter paper, which passes the liquid and
leaves the solid behind.
3. Chromatography: general name applied to a series of methods that employ a system
with two phases (states) of matter: a mobile phase and a stationary phase.
The stationary phase is a solid, and the mobile phase is either a liquid or a gas.
The separation occurs because the components of a mixture have different affinities
for the two phases and thus move at different rates.
A component with a high affinity for the mobile phase moves quickly.
A component with a high affinity for the solid phase moves more slowly.
• Paper Chromatography employs a strip of porous paper, such as filter paper, for
the stationary phase.
A line of the mixture to be separated is placed at one end of a sheet of porous
paper (stationary phase). The paper is dipped into a liquid (the mobile phase).
The paper acts as a wick to draw up the liquid.
The component with the weakest attraction for the paper travels faster than the
components that cling to the paper.
Physical Properties and Changes
• A physical property is one that can be observed without changing the chemical makeup of a
substance.
• Examples: mass, volume, boiling temperature, melting temperature, color, and conductivity.
• Extensive properties: properties that depend on sample size. In other words, a property that
changes when the size of the sample changes.
• Examples: mass, volume, weight, and length.
• Intensive properties: properties that are independent of sample size. In other words, a
property that doesn’t change when you take away some of the sample.
• Examples: color, electrical conductivity, density, hardness, melting point, and boiling point.
• A physical change is a change in the form of a substance, not in its composition.
• When water freezes or boils, its changes its state but remains water; it is still composed of
H2O molecules.
• Examples: melting, boiling, grinding, and pounding into sheets.
Chemical Properties and Changes
• A chemical property describes a chemical change (chemical reaction) that a substance
undergoes. In other words, how a substance interacts with other substances.
• Examples: flammability (the ability to catch on fire), toxicity (the ability to be poisonous),
and oxidation (the ability to react with oxygen; which causes apple slices to turn brown and
iron to rust).
• A chemical change is one in which a given substance becomes a new substance or
substances with different properties and different composition.
• Examples: combustion (burning), cooking an egg, rusting of an iron pan, and mixing
hydrochloric acid and sodium hydroxide to form water and a salt.