ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY ANDREW LAMBERT PHOTOGRAPHY / SCIENCE PHOTO LIBRARY
Universal indicator in beakers of a variety of household products. From left to right, these are vinegar, mineral water, liver salts and bleach. Universal indicator (UI) changes colour depending on whether it has been added to an acid or an alkali. Vinegar is acidic, and turns the UI red. Mineral water is neutral, and turns it yellow- green. Liver salts are less acidic than vinegar, and turn the UI orange. Bleach is a very strong alkali, and turns the UI purple.
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