What is the pH scale, and what are its minimum and maximum values?

The pH scale is a measure of how acidic or alkaline a solution is. It ranges from 0 (very acidic) to 14 (very alkaline). 

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Which pH values are acidic?

Any pH less than 7 (< 7) is acidic.

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Which pH values are neutral?

pH 7 is neutral.

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Which pH values are alkaline?

Any pH greater than 7 (>7) is alkaline.

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Give an example of a household product that is acidic.

Car battery acid / lemon juice / vinegar

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Give an example of household product that is alkaline.

Washing-up liquid / bleach / drain cleaner

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How can you measure pH electronically? 

Place a pH probe into the solution and connect it to a pH meter.


The pH meter will tell you the pH.

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How can you measure pH chemically?

Use a chemical indicator.

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What is a chemical indicator?

An indicator is a dye that changes colour based on the pH of the solution.


Some indicators, such as universal indicator, are made using multiple dyes, and show a range of colours.

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What is a 'neutralisation reaction'?

A neutralisation reaction is a reaction between an acid and a base, in which H+ ions from the acid react with OH- ions from the base.

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What ions do acids form in water?

H+

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What is a base?

A substance that can neutralise an acid.

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What is an alkali?

A base that dissolves in water to form a solution with a pH greater than 7.

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What ions do alkali form in water?

OH-

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What colour is litmus paper in alkali?

Litmus paper is blue in alkalis.

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What colour is litmus paper in acids?

Litmus paper is red in acids.

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