P1
Mixtures, Elements and Compounds in the Earth
This unit develops students’ understanding of the concepts of classification in
chemistry in the context of the planet Earth. Students investigate how substances may
occur in the various spheres as elements, compounds or mixtures.
Homogeneous
Uniform composition throughout
Heterogeneous
Non-uniform composition throughout
Impure substance
A substance contaminated with small amounts of one or more
substances
Pure substance
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Mixture
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Cannot be separated into two or more substances by
physical or mechanical means
Is homogeneous
Has constant properties throughout the sample
Fixed composition
Impure substance
Can be separated into two or more pure substances by
physical or chemical means
May be homogeneous or heterogeneous
Variable properties
Variable composition
Element
Pure substance that cannot be decomposed into simpler
substances
Compound
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Pure substance that can be decomposed into simpler
substances
Made up of two or more elements
Has the same elements present in the same ratio by mass
Has properties different from those of the elements that
make it up
Lithosphere
Crust plus the top portion of the mantle
Hydrosphere
Water of the Earth’s crust
Atmosphere
Layer of gas that surrounds the Earth
Biosphere
The portion of the Earth inhabited and used by living
organisms
Physical methods of
separating mixtures
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Filtration
Decanting
Sedimentation
Evaporation
Distillation
Fractional distillation
Separating funnel for immiscible liquids
Chromatography
Changes of state
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Solid to liquid
Liquid to solid
Liquid to gas
Gas to liquid
Solid to gas
Gas to solid
Melting point
Lowest temperature at which a solid changes to a liquid
The substance is pure if its melting point does not increase
Boiling point
Lowest temperature at which a liquid changes to a gas
The substance is pure if its boiling point does not increase
Density
Mass per unit volume
Density = mass
Volume
Gravimetric analysis
Determining the mass of substances present in a sample.
Analysis by weigh or by mass.
Elements in the
Earth’s crust
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Oxygen (46%)
Silicon (28%)
Aluminium (8%)
Iron (5%)
Calcium (4%)
Sodium (3%)
Potassium (3%)
Magnesium (2%)
Elements in sea water
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Oxygen (86%)
Hydrogen (11%)
Chlorine (2%)
Sodium (1%)
Magnesium (0.1%)
Melting, fusion
Freezing, solidification
Vaporisation, evaporation, boiling
Condensation, liquefaction
Sublimation
Condensation
Elements in living
cells
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Oxygen (60%)
Carbon (21%)
Hydrogen (11%)
Nitrogen (4%)
Calcium (3%)
Phosphorus (1%)
Chlorine (0.2%)
Sulfur (0.15%)
Elements in the
troposphere
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Nitrogen (78%)
Oxygen (21%)
Argon (1%)
Carbon dioxide (0.035%)
Neon (0.0018%)
Helium (0.0005%)
Law of conservation
of matter
Matter can neither be created nor destroyed but may be
changed from one form to another.
Metals
Are elements that have the following properties
 Solid at room temperature
 Shiny or lustrous appearance
 Good conductors of heat and electricity
 Malleable and ductile
Periodic table
The elements have been arranged in a table in order of
increasing atomic number across horizontal rows with
elements having similar properties placed in vertical columns