MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Phenolphthalein is used as a single indicator in acid-base titrations. At left it is shown in a base solution and is a pink colour. Adding a dilute acid turns it gradually colourless. At pH 9.3 (ight) the colour is barely perceivable and by pH 8 it is colourless.
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