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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…

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atmosphere by photosynthesis. 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…

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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…

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weathered. 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.…

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Limestone is mainly calcium carbonate, CaCO 3. Calcium carbonate decomposes when


it is heated producing calcium oxide and carbon dioxide. Carbon dioxide can be
detected using limewater. When the carbon dioxide is passed through the limewater it
turns it milky.


Calcium carbonate calcium oxide + carbon dioxide



CaCO3
CaO +…

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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…

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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 +…

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rid of excess stomach acid. 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.

Acid + Base Salt + Water


If…

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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,…

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ionic substance is dissolved in water or when melted. 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…

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