Indicators
and the pH scale
Solutions of acids are said to be acidic, and solutions of alkalis are said to be alkaline. If a solution is neutral , it is neither acidic nor alkaline.
Indicators are substances that change colour when they are added to acidic solutions or alkaline solutions. You can prepare homemade indicators from red cabbage or beetroot juice - these will help you see if a solution is acidic or alkaline.
Litmus and universal indicator are two indicators that are commonly used in the laboratory .
Litmus
Litmus indicator solution turns red in acidic solutions and blue in alkaline solutions - and it turns purple in neutral solutions.
Litmus paper is usually more reliable, and comes as red litmus paper and blue litmus paper. The table shows the colour changes it can make.
Red Litmus
Blue Litmus
Acidic solution
Stays red
Turns red
Neutral solution
Stays red
Stays blue
Alkaline solution
Turns blue
Stays blue
Notice how we say 'stays red' or 'turns red'. This is better than saying ' nothing ' or 'stayed the same ', because it tells us what we actually see.
Universal indicator and the pH scale
Universal indicator is a mixture of several different indicators. It has many different colour changes. Unlike litmus, universal indicator can show us how strongly acidic or alkaline a solution is, and its pH. The pH scale runs from pH 0 to pH 14.
These are the important points about the pH scale:
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