Litmus paper. Test tubes containing acidic (left) and alkaline (right) solutions, showing the colour change that litmus paper undergoes in each. At ce

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Litmus paper. Test tubes containing acidic (left) and alkaline (right) solutions, showing the colour change that litmus paper undergoes in each. At centre is dry litmus paper. Litmus is an acid-base indicator. It turns red in the presence of acids and purple in the presence of alkalis.

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Photo credit: © ANDREW LAMBERT PHOTOGRAPHY/SCIENCE PHOTO LIBRARY / Alamy / Afripics
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Keywords: acid, acidic, alkali, alkaline, base, basic, change, chemical, chemistry, colour, education, experiment, glassware, indicator, litmus, paper, results, science, solution, solutions, test, testing, tube, tubes