A titration is a technique for determining the concentration of an unknown sample solution using a solution of known concentration. Generally, the titrant from a burette is added to an unknown quantity of the analyte, which pours into the conical flask until the reaction is complete. An indicator is often used to indicate the endpoint or equivalence point.
What is a phenolphthalein indicator?
Phenolphthalein, (C20H14O4), an organic compound of the phthalene family, is a weak acid, which can lose H+ ions in solution. It is a thin, crystalline, and yellowish-white to light orange powder.
Phenolphthalein has a pKa of 9.3 and 8.20 to 10.00 is the pH range for the phenolphthalein indicator. The molecule is colourless over an acidic pH range, beginning to turn pink at pH 8.2 and becoming vivid magenta at pH 10.00 and above.
The most common application of phenolphthalein is as an indicator in acid-base titrations. It, along with thymol blue, bromothymol blue, and methyl red, is used as a component of the universal indicator.
Why is phenolphthalein used as an indicator in titration?
Phenolphthalein is used as an indicator in acid-base titration because it changes color between 8.3 and 10 pH, is economical, readily available, easily soluble, and has an endpoint that is very recognizable from either direction.
The pH of the equivalence point for an acid-base titration determines which indicator to use. Choose an indicator that changes colour at or near the equivalence point (Stoichiometric point). At this point, the titration curve will be steep, and we will get a sharp endpoint of the reaction.
When the pH rises above 07.00, phenolphthalein changes color. As a result, it works well as an indicator for the titration of strong acids and bases. It can also be used to titrate weak acids and strong bases with equivalence point above pH 07.00.
Because the equivalence point is below pH 07.00, it is not a good choice for titrations between a strong acid and a weak base. In this case, methyl orange is more suitable.
Frequently Asked Question (FAQ):
How can phenolphthalein change color?
Phenolphthalein is an indicator that changes colour depending on whether it meets an acid or a base. The phenolphthalein ion is pink, and the phenolphthalein molecule is colorless. When a base is introduced to phenolphthalein, the molecule ⇌ ions equilibrium shifts to the right, resulting in increased ionisation as the H+ ions are removed.
Which indicator is used for weak acid and a strong base?
Since the phenolphthalein indicator changes rapidly at the equivalence point, it is a good choice for weak acid and strong base titrations.
Phenolphthalein is which type of indicator?
Phenolphthalein is a synthetic pH indicator used in acid-base titration. It is a colorless, weak acid that is most commonly used in titration as an indicator to indicate the endpoint of the titration. Because this molecule dissociates to produce pink color when dissolved in water, the formation of pink color indicates the endpoint of the reaction.
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