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Phenolphthalein (/ f ɛ ˈ n ɒ l (f) θ ə l iː n / [citation needed] feh-NOL(F)-thə-leen) is a chemical compound with the formula C 20 H 14 O 4 and is often written as "HIn", "HPh", "phph" or simply "Ph" in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations.
Its sharp and easily detectable colour changes makes phenolphthalein a valuable tool for determining the endpoint of acid-base titrations, as a precise pH change signifies the completion of the reaction. When a weak acid reacts with a weak base, the equivalence point solution will be basic if the base is stronger and acidic if the acid is stronger.
Normally, the indicator causes the color of the solution to change depending on the pH. Indicators can also show change in other physical properties; for example, olfactory indicators show change in their odor. The pH value of a neutral solution is 7.0 at 25°C (standard laboratory conditions). Solutions with a pH value below 7.0 are considered ...
Paper form: It is a strip of coloured paper which changes colour to red if the solution is acidic and to blue, if the solution is basic. The strip can be placed directly onto a surface of a wet substance or a few drops of the solution can be dropped onto the universal indicator using dropping equipment.
In a titration of a weak acid with a strong base the pH rises more steeply as the end-point is approached. At the end-point, the slope of the curve of pH with respect to amount of titrant is a maximum. Since the end-point occurs at pH greater than 7, the most suitable indicator to use is one, like phenolphthalein, that changes color at high pH. [2]
A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions. [1] It forms a weak complex with the ions present in the solution, which has a significantly different color from the form existing outside the complex. Complexometric indicators are also known as pM indicators.
Chemical structure of phenolphthalein, a common phthalein dye. Phthalein dyes are a class of dyes mainly used as pH indicators, due to their ability to change colors depending on pH. [1] They are formed by the reaction of phthalic anhydride with various phenols. They are a subclass of triarylmethane dyes. Common phthalein dyes include ...
The equipment required is a colorimeter, some cuvettes and a suitable color reagent. The process may be automated, e.g. by the use of an AutoAnalyzer or by flow injection analysis . Recently, colorimetric analyses developed for colorimeters have been adapted for use with plate readers to speed up analysis and reduce the waste stream.