TREVOR CLIFFORD PHOTOGRAPHY / SCIENCE PHOTO LIBRARY TREVOR CLIFFORD PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Detecting an alkali. Beaker of sodium hydroxide solution (NaOH, left) and bottle of universal indicator (right). The beaker in the middle contains the two mixed together. Universal indicator is used to indicate acidity or alkalinity. In the bottle it is green (neutral), whereas in the middle beaker it has turned purple, as sodium hydroxide solution is alkaline.
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