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Explore the Use of Indicators

In this worksheet, students will learn about the best indicator to use to distinguish between acids and alkalis

'Explore the Use of Indicators' worksheet

Key stage:  KS 3

Year:  Year 8 Science worksheets

Curriculum topic:   Chemistry: Chemical Reactions

Curriculum subtopic:   Acids and Alkalis: Neutralisation Reactions

Difficulty level:  

Worksheet Overview

Acid or alkali? Strong acid or weak acid? Neutral solution? What pH?


There are many ways to identify whether a substance is an acid or an alkali......


One very simple method is called the litmus test. A special paper called litmus paper is dipped into the substance.


 Acids will turn litmus paper red and alkalis will turn litmus paper blue.

A neutral substance, one which is neither an acid nor an alkali, will turn litmus paper purple


There is another test, which can also tell us how acidic or alkaline a substance is - this is the pH test. You can see the pH scale below, which runs from pH0 (very acidic) to pH14 (very alkaline). There is a special solution called Universal Indicator solution. When a few drops of Universal Indicator are added to a substance, it turns a different colour. This colour matches one of the colours on the Universal Indicator scale below and that's how you determine how acidic or alkaline a substance is and so what its pH is.


pH scale


Another way to determine if something is an acid or alkali is by using a pH probe. It is a digital hand-held device that, when dipped into the solution, will give you a precise pH value for that substance - sometimes even to fine detail eg pH 13.4!


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