Chem Basics

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Chemistry In Our World
The Earth's Sea and Atmosphere
The Earth's atmosphere has changed over billions of years, but for the past 200
million years it has been much as it is today. We are, however, causing our
atmosphere to change by human activity. Burning fossil fuels and deforestation are
two examples of human effect on the environment.
The Early Atmosphere:
Scientists believe that the Earth was formed about 4.5 billion years ago. Its early
atmosphere was probably formed from the gases given out by volcanoes . It is believed
that there was intense volcanic activity for the first billion years of the Earth's
existence. The early atmosphere was probably mostly carbon dioxide, with little or no
oxygen. There were smaller proportions of water vapour, ammonia and methane. As
the Earth cooled down, most of the water vapour condensed.
The Changing
Atmosphere
As the earth cooled after the big bang, water vapour in the air condensed to form the
oceans. Carbon dioxide in the atmosphere then dissolved in the oceans. Some marine
organisms ­ such as coral, molluscs and starfish ­ use dissolved carbon dioxide to
make shells of calcium carbonate. As these creatures died, there shells fell and
became sediment. Over millions of years, all these layers of sediment built up and
became sedimentary rock.
Carbon Cycle:
Several processes, including photosynthesis, respiration and combustion, maintain the
level of carbon dioxide in the atmosphere. Green plants remove carbon dioxide from
the atmosphere by photosynthesis. Living organisms including all plants and animals
release energy from their food using respiration. Respiration and combustion both
release carbon dioxide into the atmosphere. These processes form a carbon cycle in
which the proportion of carbon dioxide in the atmosphere remains about the same .
Volcanic activity also increases the amount of carbon dioxide in the atmosphere.
Human Influences:
Burning fossil fuels produces carbon dioxide. Increased energy consumption is
leading to a rise in the use of fossil fuels, which in turn increases the release of carbon
dioxide into the atmosphere. The rising human population is adding to atmospheric
carbon dioxide in other ways too. For example when land is cleared for timber and
farms (deforestation), there are fewer trees to remove carbon dioxide from the

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If the fallen trees are burned or left to rot, additional
carbon dioxide is released into the atmosphere. This is particularly important when
forests are cleared to make way for farms: not only are there then fewer trees to
absorb carbon dioxide, but the burning of the trees releases carbon dioxide .
Oxygen In The Atmosphere
Oxygen is a very important gas in the air that is essential for humans. If our
bodies don't have enough oxygen it can cause headaches, sickness and
eventually death.…read more

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A river carries, or transports, pieces of broken rock as it flows along. When the river
reaches a lake or the sea, its load of transported rocks settles to the bottom. We say
that the rocks are deposited. The deposited rocks build up in layers, called sediments.
This process is called sedimentation. The weight of the sediments on top squashes the
sediments at the bottom. This is called compaction.…read more

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Chemical weathering can hollow out caves form and make cliffs fall away. When
fossil fuels such as coal, oil and natural gas are burned, carbon dioxide and sulphur dioxide
escape into the air. These dissolve in the water in the clouds and make the rainwater more
acidic than normal. When this happens, we call the rain 'acid rain'. Acid rain makes chemical
weathering happen more quickly. Buildings and statues made from rock are damaged as a
result.…read more

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Substances are made of atoms. An atom is the smallest part of an element that can
take part in chemical reactions. A compound consists of the atoms of two or more
different elements chemically joined together. The chemical formula of a compound
shows the symbols of the elements it contains and the ratios in which their atoms are
present. In all chemical reactions the atoms of the reactants rearrange to form new
products.…read more

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Calcium carbonate calcium oxide + carbon dioxide
CaCO3 CaO + CO2
Carbon dioxide gas can be detected using limewater. Limewater turns cloudy white
when carbon dioxide is bubbled through it.
Making Limewater:
When limestone is heated, he calcium carbonate that it contains forms calcium oxide.
Calcium Carbonate Calcium Oxide + Carbon Dioxide
CaCO3 (s) CaO (s) + CO
2 (g)
A vigorous reaction happens when water is added to calcium oxide.…read more

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Antacids contain bases (substances that react with acids).
The neutralization reaction between an acid and a base produces water and a
compound called a salt. Some bases are soluble. A base dissolved in water is called an
Alkali.…read more

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The name of the salt produced in a neutralisation reaction can be predicted. The first
part of the name is `ammonium' if the base used is ammonia. Otherwise, it is the
name of the metal in the base. The second part of the name comes from the acid used:
Chloride, if hydrochloric acid is used
Nitrate, if nitric acid is used
Sulphate, if sulphuric acid is used
Phosphate, if phosphoric acid is used.…read more

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Positively charged ions move to
the negative electrode during electrolysis. They receive electrons and are reduced.
Negatively charged ions move to the positive electrode during electrolysis. They lose
electrons and are oxidised. The substance that is broken down is called the electrolyte.
At the negative electrode:
Positive ions gain electrons at the negative
electrode, so are reduced.…read more

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