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Neutralisation


Neutralisation


What are acids and alkalis?


What are bases?

All alkalis are bases. Bases are substances that react

with acids by absorbing hydrogen ions (H+).

Some bases are soluble in

water. These are called alkalis.

All alkalis contain hydroxide ions

(OH–). The more OH– ions in the

solution, the stronger the alkali.

The oxides, hydroxides and carbonates of metals, such as

sodium hydroxide, are bases.


1 2 3 4 5 6 7 8 9 10 11 12 13 140

What is the pH scale?

The pH scale runs from 0 to 14. The numbers 0 to 6

represent acidic conditions and 8 to 14 represent alkaline

conditions. A pH value of 7 is neutral.

What are the pH values of some everyday items?

increasing acidity increasing alkalinity


What does the pH scale show?


What is the order of pH?


Investigating changes in pH


What are indicators?

Indicators are chemicals that change colour in the presence

of an acid or an alkali.

There are many different indicators. Lots of them come

from plants, like red cabbage. Different indicators turn

different colours.

Universal indicator is a mixture of indicators. It is useful

because it shows a range of colours from pH 1–14.

Geranium plants grown

in acidic soil have red

flowers, while geraniums

grown in alkaline soil

have blue flowers.


Acids and bases – true or false?


Neutralisation


How are salts made and named?

When an acid reacts with a base, a neutralisation

reaction occurs and produces a chemical called a salt.

The name of the salt depends on the names of the reactants.

The first part of the salt’s name comes from the base:

e.g. sodium hydroxide sodium…

The second part of the salt’s name comes from the acid:

e.g. sulfuric acid …sulfate

For example, if sodium hydroxide neutralises sulfuric acid,

the product is a salt called sodium sulfate.

+acid base salt + water


Naming salts


What is the name of the salt?


pH change during neutralisation


Using salts

Table salt is sodium chloride.

This is the salt used to flavour

and preserve food.

Indigestion remedies often

contain magnesium salts.

All oceans, seas, rivers and

lakes on Earth contain some

dissolved salts.

The colours of fireworks are

formed when salts burn.

Calcium chloride, for example,

burns a bright orange colour.


Neutralisation in your stomach

A human stomach contains large amounts

of hydrochloric acid.

Indigestion occurs when the stomach

produces too much acid. Indigestion

remedies, sometimes called antacids,

contain a base which neutralises the

excess acid, relieving symptoms.

provides a low pH for the digestive

enzymes to work

Hydrochloric acid in the stomach:

helps kill harmful bacteria in food.


Neutralisation


Water is formed because OH– ions from the alkali react with

H+ ions from the acid to produce molecules of water (H2O).

Making salts: acid + alkali

When an acid reacts with an alkali, the products are a salt

and water.

acid alkali salt water+ +

For example:

+ +

++

sodium

hydroxide

NaOH (aq)

sodium

chloride

NaCl (aq)

water

H2O (l)

hydrochloric

acid

HCl (aq)


When is the reaction complete?

This can be used in titrations to determine the concentration

of acids and alkalis.

The reaction between sodium hydroxide and hydrochloric

acid produces sodium chloride, which is soluble in water.

+ +

++

sodium

hydroxide

NaOH (aq)

sodium

chloride

NaCl (aq)

water

H2O (l)

hydrochloric

acid

HCl (aq)


What is a titration?


Making salts: acid + metal oxide

When a metal oxide is mixed with an acid, the products

are a salt and water.

calcium

chloride+ water

calcium

oxide

CaO (s)

hydrochloric

acid

2HCl (aq) CaCl2 (aq) +

+

+ H2O (l)

For example:

acid metal oxide salt water+ +

Water forms because oxygen ions, O2-, from the oxide join up

with H+ ions from the acid to produce molecules of water (H2O).


Obtaining salts from metal oxides

When a metal oxide is added to an acid, it dissolves as

it reacts.

How could the solid copper sulfate salt be separated

from the water?

When the metal oxide stops dissolving, it means that

all of the acid has reacted.

+ +copper

oxide

CuO (s)

sulfuric

acid

H2SO4 (aq)

copper

sulfate

CuSO4 (aq)

water

H2O (l)+ +


Obtaining salts from copper oxide


Making salts: acid + carbonate

When a carbonate is mixed with an acid, the products are

a salt, carbon dioxide and water.

copper

nitrate+ water +

carbon

dioxide

copper

carbonate

CuCO3

(s)

nitric

acid

2HNO3

(aq)

Cu(NO3)2

(aq)+

+

+ H2O

(l)+ CO2

(g)

For example:

acid carbonate salt water+ +carbon

dioxide+

Water and carbon dioxide are formed because the

carbonate ions (CO32-) react with H+ ions from the acid.


Making salts: acid + metal

When a metal is added to an acid, the products are a salt

and hydrogen gas.

For example:

This method of making salts only works with some metals.

hydrochloric

acid

2HCl (aq)

+

+

+

+

zinc

Zn (s)

zinc

chloride

ZnCl2 (aq)

hydrogen

H2 (g)

acid metal salt hydrogen+ +

What would happen if potassium was used? Or copper?


Which metal will react the most?


Making salts – summary

Salts can be made by reacting acids with bases in a

neutralisation reaction. Three examples of this are:

Another way of making a salt from an acid is:

acid + alkali

acid + metal oxide

acid + carbonate

salt + water

salt + water

salt + carbon dioxide + water

acid + metal salt + hydrogen


Neutralisation


Matching reactants and salts


Complete the neutralisation reaction


Balancing equations


Neutralisation


Glossary


Multiple-choice quiz

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