Acids and alkalis

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The most recognisable and common weak alkali is ammonia.

Slide 10

Indicators

They change colour in acid or alkaline solutions.

Different indicators change to different colours.

Indicators help you find out whether a solution is acidic or not.

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Litmus Test

Litmus is an indicator. It changes colour in acid and alkaline solutions.

Litmus is red in an acid.

Litmus is blue in an alkali.

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Universal Indicator

Universal indicator changes colour in acids and alkalis.

Its colour shows the strength of an acid or alkali.

ACIDS

ALKALIS

Neutral

Slide 13

The pH scale

1 – 6

8 - 14

Alkalis

7

Neutral

Acids

Slide 14

Applications of Neutralisation

Indigestion: Our stomach carries

around hydrochloric acid.

Too much of this leads to indigestion.

To cure indigestion, you can neutralise the excess acid with baking soda or specialised indigestion tablets.

Insect Stings

Bee stings are acidic

and can be neutralised with

baking soda (bicarbonate of soda).

Wasp stings are alkaline and can be neutralised with vinegar.

Slide 15

More Applications of Neutralisation

Factory Waste: Liquid waste from factories is often acidic. If it reaches a river it will destroy and kill sea life of many forms. Neutralising the waste with slaked lime can prevent this.

Soil Treatment: When soils are too acidic (often as a result of acid rain) they can be treated with slaked lime, chalk or quicklime, all alkalis. Plants and crops grow best in neutral soils.