Chemical Earth Summary

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Chemistry Summary

The particle theory:

1. Matter is made of tiny particles

2. Particles of matter are in constant motion

3. Particles of matter are held together by very strong electric forces

4. There are empty spaces between the particles of matter that are very large compared to the particles themselves.

5. Each substance has unique particles that are different from the particles of other substances

6. Temperature affects the speed of the particles.  The higher the temperature, the faster the speed of the particles.

The Biosphere, Lithosphere, Hydrosphere and Atmosphere contain mixtures of elements and compounds.

• Biosphere – consists of all living organisms and their life cycles. The most abundant elements are oxygen (60%), carbon (21%) and hydrogen (11%), which are mostly found within the DNA of living things and organic compounds such as amino acids, carbohydrates, fats and proteins.

• Atmosphere – is the layer of gas surrounding the earth and is a mixture composed mostly of uncombined lighter elements, although composition varies according to location or climate. The two most abundant elements are nitrogen (75.3%) and oxygen (23.2%), which occur in their gaseous forms or in compounds like carbon dioxide.

• Lithosphere – is made up of the crust and the solid top of the mantle, and is composed mostly of rocks and soil (mixtures of minerals), which can have a definite composition or a range of compositions. Elements such as oxygen (47%), silicon (28%), aluminium (8%) and iron (5%) occur in silicate, oxide and carbonate minerals. Pure elements such as gold also occur in their pure form (uncombined) in the lithosphere.

• Hydrosphere – is all the water on earth and is a discontinuous sphere. It has a varied composition (i.e., salt and fresh water), and is mainly made up of the compound water (H2O) but also contains many water soluble sulfates and soluble carbonates, and elements like chlorine and sodium dissolved as ions.

Separation Procedures: - usually separations require a number of processes or procedures to separate the constituent substances from a mixture. These separations are physical separations.

• Filtration – separates undissolved solids from liquids or gases by passing the mixture through a screen such as filter paper which is fine enough to collect the particles of the solid.

• Solution – usually used in combination with another separation method, and is based on the fact that some constituents in a mixture dissolve in a solvent such as water more readily than others. That is, a mixture is added to a solvent and can be separated through the fact that one constituent will dissolve more readily than the others (although to fully separate the mixture, another method such as filtration would have to be used).

• Evaporation – relies upon the varying evaporating points of the constituent substances within a mixture. A mixture is heated (in an evaporating basin and the process is usually sped up using a Bunsen burner) and one substance will evaporate, leaving the other substance behind.

• Crystallisation - depends on the components of the mixture having different solubilities in a selected liquid (usually water) at different temperatures. For example, a mixture of salt and baking powder are both soluble in hot water, but when the hot water (with the mixture dissolved in it) is cooled, the baking soda will crystallise because it is much less soluble at cooler temperatures.

• Sedimentation – occurs when solid particles are allowed to settle from water (or other liquids) or air. This occurs most readily when the solvent is not moving.

• Decantation – the process of pouring off a liquid above a solid which has been allowed to settle by sedimentation.

• Sieving – the process of separating solid particles of various sizes.

• Centrifugation – involves a centrifuge that spins and separates...
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