Year 11 Module 1 – The Chemical Earth
The Earth is made up of a large number of different substances: elements, compounds & mixtures
We can classify elements & compounds as pure substances. These are always HOMOGENEOUS. Mixtures are not pure substances and can be either homogeneous or HETEROGENEOUS.
Pure substances have a fixed composition
eg copper metal, sulfur, carbon dioxide (CO2), methane (CH4).
Mixtures have variable composition and can also be separated into its components relatively easily. Eg. Alloys – brass Cu: 65% Zn 35%
Elements are pure substances that cannot be broken down into any other substance. Compounds can be broken down, but this requires chemical means and is not as easy as separating mixtures.
The Spheres of the Earth
and give an example of a mixture
found in each.
Solids of different sizes - seiving
Solids & liquids – evaporation, filtration, distillation, decanting
Dissolved solids – crystallisation by evaporating
Solvents - distillation
Two liquids – immiscible liquids using a separating funnel -
fractional distillation due to different boiling points
H/W – P.18 Qu. 11-18
Identifying Pure Substances
Colour – some substances have a characteristic colour, eg CuSO4 = blue. We can use this knowledge in a qualitative way to determine if a sample has impurities.
Melting & Boiling Point – The mp & bp of a substance is a good indicator of its purity. A pure substance will have a sharp melting point and its mp & bp will not change after further attempts at purification.
Impurities can lower or raise bp, but only lower mp.
Density = mass/volume – pure substances have characteristic densities – eg glass.
This is a method used to determine the composition by mass of a substance. •
Mining – determine the % of a mineral in an ore deposit •
Quality control of products
Determining the composition of a product made by a rival company •
Composition of a soil
Pollutant in air or water
Calculating % composition
% A in ABC =
mass of A present
Mass of total sample (ABC)
Eg % BaSO4 in Ore sample
3.61g of sample
Mass of BaSO4 = 1.52g
Mass of MgSO4 = 2.07g
Total returned mass = 3.59g
% BaSO4 = 1.52/3.61 x 100 = 42%
% MgSO4 = 100 – 42 = 58 %
= 2.07/3.61 x 100 = 58%
P.25 Qu 26 & 27
for 26 → 1 ppm = 1 mg/L
Physical Properties & Uses of Elements
Metals & non-metals have differing properties. The properties of an element will determine what it is used for. Metals Shiny, ductile, malleable, good conductors of electricity, variable (but mostly high melting point) Eg –
Gold – jewellery as it’s shiny
Aluminium, Iron – car parts as malleable
Copper – wire as it is ductile, a very good conductor
Tungsten – light bulb filaments due to v. High m.p
Non-metals: Dull, poor conductors, brittle, usually soft, variable mp (v.low – v.high) Eg.
Carbon (graphite) can conduct, so used as electrodes
Carbon (diamond) used a tools
Liquid N2(l) used in cooling
Some elements have properties of both metals & non-metals, these are classified as semi-metals or metalloids Eg silicon.
Comparing Chemical & Physical Changes
Chemical changes are reactions – they are difficult to reverse, at least one new substance formed, mass will be conserved, often a large input/output of heat.
Physical changes – No new substances are formed, easily reversed and only small energy changes are required/produced. E.g
2H2O(l) + E → 2H2(g) + O2(g) – chemical change
H2O(l) + E → H2O(g) – physical change
Other physical changes are: freezing, melting, condensing, evaporating, subliming, dissolving & crystallisation.
In the electrolysis of H2O
Negative electrode: 4H+(aq) + 4e- → 2H2(g)
Positive electrode: 4OH-(aq) → O2(g) + 2H2O(l) + 4e-
Evidence of Chemical Reactions
New products formed (eg...
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