Chemistry

The Early Atmosphere

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The Early Atmosphere

It was extremly volcanic in the early atmosphere. 

The volcanoes spewed out a lot of gas which created the early atmosphere. These gases were carbon dioxcide, methane and steam which is covered in a thick layer of sulphur dioxcide. There was no oxygen for two million years

Stromatilites were one of the first types of life on earth, they released oxygen and photosynthesised because they had chloraphyll. 

6 Co2 + 6 H 2o ---- Light ------ C6 H12 O6 + O2

The stromatilites have been around for three and half thousand million years. The seas were rich with iron, from the volcanoes.

Iron oxide (rust) formed. This stopped the O2. It then left the oceans, it filled the atmosphere which acted as a sheild - the O zone layer. 

See diagram/graph in book.

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Gases in the Atmosphere

Oxygen ---------- 21%

Nitrogen ---------- 78%

Carbon dioxide ------------ 0.5%

Others ------------ 0.95% 

See workings out for a pie chart and the chart itself in book.

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Rocks

Sedimentary example - limestone. Lots of minerals are out under pressure, water is squeezed out forming the rock. This happens underwater. 

Metamorphic  example - slate. The heat and pressure compress over long periods of time.

Igneous example - granite or basalt. These are formed when volcanoes erupt and the magma melts. The quicker it cools, the smaller the crystals are. Basalt is a quick cooloing rock. Whereas granite takes longer to cool. Basalt is extrusive (above ground) and granit is intrusive (under ground). Porous is when there are tiny holes in the rock that can absorb water, acid etc. Pumice is an example of a porous rock. 

From the mountain it crumbles into the sea -------- Igneous  (crumbles and compresses)

Forms a layer of sediment -------------------- Sedimentary 

Compresses ------------------------ Metamorphic (heat + pressure with a chemical change)

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Thermal Decomposition Of CaCo3

Limestone is mainly calcium carbonate - CaCO3.

When its heated it thermally decomposes to make calcium oxide and carbon dioxide. 

Thermal decompisition happens whrn one sunstance chemicallly changes into at least two new substances when it's heated. 

Calcium carbonate --- calcium oxide + carbon dioxide 

    CacO3              ---       CaCO       +      CO2

See the three step cycle in  my book. 

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Variables

Independent variable - the thing you'e going to change

Dependent variable - the thing you're going to measure

Controlled variable - the things you're going to keep the same 

It's really important to know these when you're carrying out an experiment and when writing and evaluating your conclusion. 

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Neutralisation

An acid and a base react together to form a salt and water. The products of the reaction aren't strongly acidic or alkaline - they're neutral. So it's called a neutralisation reaction.

The equation is: acid + base ---- salt + water

A solid = high concentration

The hydrogen makes the acids reactive. 

The colour is to do with the strength of the acid.

The salts that are produced have many uses. Such as iin fertilisers and in fireworks and colouring agents (e.g. - calcium chloride for an orange colour).

See book for these acid reaction examples.

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Electrolysis

  • Electrolysis is the seperation of a compound, into the elements using electricity.
  • This has to be done using a solution.
  • This solution is the electrolyte.
  • These components are then released as atoms or molecules - often as a gas. 
  • The electricity has to be a D.C current (such as a battery).

You can electrolyse hydrochloric acid. When you do this the d.c current causes the acide to decompose into its two parts: hydrogen gas and chlorine gas. 

See rough diagram in book. 

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Extracting Metals

Two ways you can extract metals are:

  • Underground mining
  • Metal detectors.The more reactive a metal the softer it is. This is in order of getting more reactive as we go along.

Lithium Hydrogen comes off it turning it into an alkali, because the univeresal indicator turns it purple.

Sodium The reaction is the same as lithium but much more.

PottasiumMost reactive, lots of hydrogen.

This is a ryme to help you remember the order of how reactive these metals are.

Peters simple little cousin met a zulu in the lake carrying silver + gold. 

Pottasium, sodium, lithium, calcium, magnesium, aliminuim, zinc, iron, tin, lead, copper, silver + gold. 

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Reduction

Reduction is when a stonger metal bumps off a weaker metal and then takes the oxygen. When you find a metal (except gold and silver) it is an oxide, you need to get rid of the **** (dirt and impurities). 

FeO + AL ------- ALO + Fe

2FeO + C -------- CO2 + 2Fe

   (the 'girl' is the oxygen the weaker metal is the iron and the carbo in the stronger metal.) 

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