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CAMBRIDGE SECONDARYONE SCIENCECHAPTER 7: SALTS
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7.1 WHAT IS A SALT?
Saltsare compounds that have hundredsof different uses in everyday life.
Usesof salts
Calcium sulfateis used to make
blackboardchalk
Magnesiumcarbonate is usedin sports to makehands dry, so they
do not slip
Aluminium sulfateis added to dyesto help them stick
to fibres
Ammoniumnitrate is used asfertilisers to helpcrops grow well
Copper sulfate isused to stop fungal
growth on soyaseeds when they
are planted
Sodium chloride is
used to preservefood and as tablesalt to flavour food
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7.1 WHAT IS A SALT?
Calcium sulfate is
used as
blackboard chalk
Magnesium
carbonate is used
as sport powder
Aluminium sulfate
is added to dyes
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7.1 WHAT IS A SALT?
Ammonium
nitrate is used as
fertiliser
Copper sulfate is
used to stop fungal
growth on soya seeds
Sodium chloride is
used as preservative
and flavouring
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7.1 WHAT IS A SALT?
Saltsare formed when thehydrogen in anacid is replaced by a metal or ammonium.Name of acid Formula Salts formed
from the acid
Example of
salt
Formula
of salt
Hydrochloricacid
HCI Chlorides Sodiumchloride
NaCI
Sulfuric acid H2SO4 Sulfates Copper
sulfate
CuSO4
Nitric acid HNO3 Nitrates Potassium
nitrate
KNO3
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7.2 PREPARING A SALT USING METAL AND ACID
Salts can beprepared by reactingmetalswith acids.
The general word equation for the reaction
of metals with acid:
Acid + Metal Salt + Hydrogen
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7.2 PREPARING A SALT USING METAL AND ACID
The word equation for the reaction betweenzinc and hydrochloric acid:
Zinc + Hydrochloric Zinc + Hydrogen
acid chlorideTo obtain a dry sampleof the salt, you
must allow the water to evaporate from
the salt solution.
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7.2 PREPARING A SALT USING METAL AND ACID
Steps in preparing a salt using metal and acid
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7.2 PREPARING A SALT USING METAL AND ACID
Unreactive metals such assilver andcopper will not react with acids. This is
because these metalscannot displace
hydrogen from an acid.
To make salt from unreactive metals, the
metal oxides of the metals are used to
react with acids.
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7.2 PREPARING A SALT USING METAL AND ACID
Steps in preparing a salt using metal oxide and acid
Filter paperCopper oxide
powder
Dilute sulfuric
acid
Funnel
Filter paper
Unreacted
copper oxide
powder
Copper
sulfate
solution
Evaporating
dish
Copper
sulfate
solution
Bunsen
burner
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7.3 METAL CARBONATES AND ACIDS
Carbonatesare formed by the reactionof a metalwith carbonic acid.
Carbonatescan be used to form other
salts by reacting them with an acid.
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7.3 METAL CARBONATES AND ACIDS
The general word equation for the reaction
between acids and carbonates:
Acid + Carbonate Salt + Water + Carbon
dioxideThe word equation for the reaction between
sulfuric acid and calcium carbonate:
Sulfuric + Calcium Calcium+Water+Carbonacid carbonate sulfate dioxide
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7.3 METAL CARBONATES AND ACIDS
Steps in preparing a salt using carbonate and acid
Copper
carbonate
Dilute
hydrochloric
acid
Stirring rod
Filter paperFunnel
Unreacted
copper
carbonate
Copper
chloride
solution
Bunsen
burner
Copper
chloride
solution
Evaporating
dish
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7.4 FORMING SALTS BY NEUTRALISATION
Saltsare formed when an acidis
neutralised by an alkali.
The general word equation for
neutralisation reaction:
Acid + Alkali Salt + Water
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7.4 FORMING SALTS BY NEUTRALISATION
The word equation for the reaction
between sodium hydroxide solution and
hydrochloric acid:
Sodium + Hydrochloric Sodium + Water
hydroxide acid chloride
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7.4 FORMING SALTS BY NEUTRALISATION
Steps in preparing a salt using neutralisation reaction
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7.4 FORMING SALTS BY NEUTRALISATION
Metal oxides are called bases.
Soluble bases formalkalis when they
dissolve in water.
The word equation for the formation of alkali
when sodium oxide dissolve in water:
Sodium oxide + Water Sodium
hydroxide
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7.4 FORMING SALTS BY NEUTRALISATION
Some bases are insoluble in water, for
example, iron oxide and copper oxide.
They do not form alkalis. However they can
still react with acidsto form salts.The word equation for the reaction between
copper oxide and sulfuric acid:
Copper + Sulfuric Copper + Wateroxide acid sulfate
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