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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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