RHYS LEWIS & MINH TAN PHAM, AHS, DECD, UNISA / SCIENCE PHOTO LIBRARY RHYS LEWIS & MINH TAN PHAM, AHS, DECD, UNISA / SCIENCE PHOTO LIBRARY
Acid-base titration. Timelapse footage of the stages in an acid-base titration analysis. The clip starts with 250 millilitres of an acid in a volumetric flask being poured into a beaker. A graduated pipette is used to withdraw a precise volume (20 millilitres) for use in the titration. The clip then shows a burette being filled with 50 millilitres of an alkaline solution via a glass funnel. The view changes to show a conical flask (containing the 20 millilitres of acid previously measured out) with the burette positioned above it. The demonstrator is adding phenolphthalein indicator to the acid. This indicator is colourless in acid solutions, turning pink in basic (alkaline) solutions. The burette tap is opened and the alkali added with the flask swirled to mix the chemicals. The endpoint of the reaction occurs when the solution goes permanently pink. The end of the clip shows this endpoint reached by dropwise addition of the alkali. The precise volumes and concentrations used in such titrations allow calculation of an unknown concentration. The reagents used here are sodium hydroxide (NaOH) and hydrochloric acid (HCl).
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