TREVOR CLIFFORD PHOTOGRAPHY / SCIENCE PHOTO LIBRARY TREVOR CLIFFORD PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Adding acid to an alkali. Beaker of hydrochloric acid solution (HCl, left) and bottle of universal indicator (right). The beaker in the middle contains sodium hydroxide (NaOH) solution and universal indicator mixed together. HCl has been added with a pipette. Universal indicator is used to indicate acidity or alkalinity. In the bottle it is green (neutral). NaOH is alkaline, however the indicator is orange in the middle beaker as enough acid has been added to make the solution acidic.
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