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Flourine, Chlorine, Bromine, Iodine.

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When you get tired of reading- watch a video.

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The strengths and weaknesses of acids and bases - George Zaidan and Charles Morton

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0-6 is an acid.
7 is neutral.
8-14 is alkaline.

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Bases are very corrosive

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Lithium, Sodium, Potassium, Rubidium, Caesium, Francium.

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All of the information you need and a quiz at the end.

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Pure water is neutral, and so is petrol.

An is a substance that changes colour when it is added to acidic 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. 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'. This is better than saying 'nothing' or 'stayed the same', because it tells us the colour we actually see.

Universal indicator and the pH scale

Universal indicator is supplied as a solution or as universal indicator paper . It is a mixture of several different indicators. Unlike litmus, universal indicator can show us how strongly acidic or alkaline a solution is, not just that the solution is acidic or alkaline. This is measured using the , which runs from pH 0 to pH 14.

Universal indicator has many different colour changes, from red for strongly acidic solutions to dark purple for strongly alkaline solutions. In the middle, neutral pH 7 is indicated by green.

When you use universal indicator paper, you get more accurate results if you only put a small spot of the test solution on the paper, and then leave the colour to develop for about 30 seconds before comparing it with the colour chart.

These are the important points about the pH scale:

neutral solutions are pH 7 exactly

acidic solutions have pH values less than 7

alkaline solutions have pH values more than 7

the closer to pH 0 you go, the more strongly acidic a solution is

the closer to pH 14 you go, the more strongly alkaline a solution is

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The pH scale and neutralisation - Revision 1 - KS3 Chemistry - BBC Bitesize

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Pure water is neutral, and so is petrol. An is a substance that changes colour when it is added to acidic 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.