Preliminary Chemistry. 'The Chemical Earth'

Topics: Water, Oxygen, Chemistry Pages: 11 (2041 words) Published: November 18, 2013
Chemical Earth
1. The living and non-living components of the Earth contain mixtures

Construct word and balanced formulae equations of chemical reactions as they are encountered 1. Build a word equation
Reactants on left, Products on right
2. Convert word equation into chemical formula for the reactants and products Using valency rules
3. Balance the equation
Adjust coefficients to get equal numbers of each kind of atom on each side 4. Specify the physical state for each species present
(s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous or dissolved in water

Example
1. Phosphorus + chlorine  phosphorus trichloride
2. P + Cl2 PCl3
3. Atoms on either side of the arrow are not balanced
Reactants: P = 1, Cl = 2
Products: P = 1, Cl = 3
Insert coefficients to make balanced
2P + 3Cl2 2PCl3
4. 2P(s) + 3Cl2(g) 2PCl3(l)

Identify the difference between elements, compounds and mixtures in terms of particle theory

Homogenous : Has the same type and distribution of particles throughout and an uniform composition. E.g. Pure water, sugar, aluminium
Heterogeneous : Having non-uniform composition where there are recognisable small pieces of material Impure substances: are mixtures
Contaminated with small amounts of one or more other substances Elements: Pure substances which cannot be decomposed into simpler substances Compounds: Pure substances which can be decomposed into simpler substances 2 or more elements

E.g. Table salt (sodium chloride), water and elements.
Atoms: The particles that make up elements
An atom is the smallest particle of an element which is still recognisable as that element. A molecule: Smallest particle of a substance that is capable of separate existence.

Identify that the biosphere, lithosphere, hydrosphere and atmosphere contain examples of mixtures of elements and compounds

The various ‘spheres’ of Earth
Biosphere: The portion of Earth inhabited and used by living matter Consists of atmosphere, hydrosphere and lithosphere
Mixtures: wood, blood, sugarcane
Compounds: Carbohydrates, sugars, proteins, fats, vitamins
Elements: Oxygen, carbon, hydrogen, nitrogen, calcium etc
Lithosphere: Crust plus the top portion of the mantle
Mixtures: Rocks, sand, soils, mineral ores, coal, oil and natural gas Compounds: Silicon, soils containing aluminium, carbon
Elements: Gold, silver, platinum and carbon (diamond)
Hydrosphere: The water of the Earth’s crust
Salt water of the oceans, fresh water of rivers and lakes, and ground water Compounds: Sea water, carbon dioxide, calcium chlorides, sulfates Atmosphere: Layer of gas about 200 to 300km thick which surrounds the planet Mixture of gases

Elements: Nitrogen, oxygen and argon
Compounds:Water, carbon dioxide, nitrogen dioxide, sulphur dioxide and carbon monoxide

Identify and describe procedures that can be used to separate naturally occurring mixtures of

Solids of different sizes
Solids and liquids
Dissolved solids in liquids
Liquids
Gases

Separating Solids of different sizes
Sieving
Sieves are used to separate small particles from larger ones. E.g. Fine sand needed for making concrete is separated from the coarser material (gravel) by sieving. Separating Solids and Liquids
Filtration
Liquid or solution passes through the paper while the suspended solid remains on the top of the filter paper. The filtrate is the liquid/solution which passes through the paper. E.g. Sand being separated from sea water.

Sedimentation
Solids settle to the bottom of a container.
E.g. Mud settle to bottom of muddy water.
Decantation
Carefully pouring the liquid off and leaving the solid undisturbed as the bottom of the container. E.g. Pouring tea off tea leaves.
Separating Dissolved Solids in Liquids (Solutions)
To gain the solid from the solution:
Evaporation
Substances in mixture must have different volatilities.
The liquid evaporates quicker than other, leaving other behind. E.g. Salt is...
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