TWEEDRIVERHIGH SCHOOL

2006

PRELIMINARY CHEMISTRY

Unit 1

The Chemical Earth

Part 1

  1. The living and non-living components of the Earth contain mixtures.
  • Identify the difference between elements, compounds and mixtures in terms of particle theory.

Homework: Briefly revise the Particle Theory of Matter.

Atom

An atom is the smallest particle of an element that can take part in a chemical reaction.

Molecule

A molecule is the smallest particle of a substance capable of separate existence.

List two examples:

1.

2.

Mixture

If a sample of matter is not a pure substance, then we call it a mixture.

An impure substance is one substance contaminated with small amounts of other substances. It is therefore a mixture.

Homework: Give two examples of a mixture.

1.

2.

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

Homework:

Draw the structure of the earth identifying the internal structure and the above spheres.

The Biosphere

The biosphere is that part of the earth in which living organisms live out their life cycles.

All living things on earth are composed of compounds based on carbon. All living things are mixtures.

Other elements essential to living things include oxygen, hydrogen, nitrogen sulfur and phosphorus.

The Lithosphere

The lithosphere is composed of mostly rocks and soil. The main elements are silicon and oxygen.

The Atmosphere

The atmosphere is a mixture composed mainly of the gases Nitrogen, Oxygen, and Argon with small percentages of compounds such as carbon dioxide, methane and water.

Homework: Draw a table showing the composition of the atmosphere.

Atmosphere Table

The Hydrosphere

The hydrosphere includes the earths oceans, seas, lakes, rivers and underground water.

The hydrosphere is a mixture of mainly water plus compounds containing Chlorine, Sodium, Magnesium, Potassium, Calcium, Sulfur and Bromine.

  • 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

Separation of Mixtures

  1. Separation of solids of different sizes.
  • For metal ores, crushing and sieving methods may be used.
  • The process of froth flotation is widely used for sulfide ores.

Homework: Briefly outline the process of ‘froth flotation’.

  • Magnetic properties are used to separate minerals in black sands, eg rutile and ilmenite.

What must these minerals contain?

  1. Solids and liquids.

a)Centrifuging – used to separate small amounts of solids in suspension.

b)Filtration – used to separate insoluble solids from a liquid.

  1. Dissolved solids in liquids.

Dissolved solids in liquids are solutions.

a)Evaporation – the liquid is evaporated to dryness and the soluble solid remains.

b)Crystallisation – the slow cooling of a hot saturated solution. Crystals will appear as the compound is less soluble at a cooler temperature.

Solubility Rule: Solubility increase with increasing temperatures, (except for gases where solubility decreases with an increase in temperature.)

  1. Separating liquids.

a)Soluble liquids

Soluble liquids are separated by the process of distillation.

Distillation uses the different boiling points of the liquids to separate them.

The following diagrams outline:

1. A simple distillation apparatus

2. A fractionating column for refining crude petroleum.

b)Separating immiscible (do not mix) liquids.

A separating funnel is used to separate immiscible liquids such as oil and water.

  1. Separating gases in air.
  2. Air is passed through filters to remove particulate matter.
  3. Air is passed through a solution of sodium hydroxide to remove carbon dioxide.
  4. Water is removed as ice by cooling to -25C
  5. The air is then compressed and cooled until it liquefies, -200C.
  6. The liquid is allowed to boil and the different gases are collected in a fractionating column.

Boiling points of various gases:

Nitrogen = -196C

Argon = -186C

Oxygen= -183C

Homework:

Briefly outline the following separation techniques:

  • Sedimentation
  • Decantation
  • Sieving
  • Chromatography

Practical

Homework:

Plan, choose equipment and perform a first hand investigation to separate a mixture of sand, salt and water.

Your investigation must include the following points:

  • Aim
  • Risk Assessment
  • Method
  • Gravimetric analysis giving percentage composition, by mass.
  • Results
  • Discussion
  • You will then perform the experiment in the lab.
  • Describe situations in which gravimetric analysis supplies useful data for chemists and other scientists.
  • Mining

a)Assays of ore bodies to see if mining is viable.

b)Assays of ore to be shipped for further treatment to determine its export value.

  1. Factories (Quality Control)

a)Alloy manufacture to determine if the alloy is within specifications.

b)Determining the level of impurities in products, e.g. iron in bronze

  1. Analysis of paints to check for lead content.
  2. Impurities in food stuffs, e.g. sulfur content in tomatoes.
  3. Manufacture of drugs, to check level of drug in tablets is accurate.

Assignment:

Due Date:

Identify data sources, gather, process and analyse information to identify the industrial ‘Bayer’ process for refining bauxite ore.

Use available evidence to:

-Identify the properties of the mixture used in its separation.

-Identify the product(s) of separation and their uses.

-Discuss issues associated with wastes from the processes used.

1