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The discovery of phenolphthalein's laxative effect was due to an attempt by the Hungarian government to label [clarification needed] genuine local white wine with the substance in 1900. Phenolphthalein did not change the taste of the wine and would change color when a base is added, making it a good label in principle.
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.
Color change In some reactions, the solution changes color without any added indicator. This is often seen in redox titrations, for instance, when the different oxidation states of the product and reactant produce different colors. Precipitation If the reaction forms a solid, then a precipitate will form during the
Acid–base titration is also utilized in the analysis of acid rain effects on soil and water bodies, contributing to the overall understanding and management of environmental quality. [24] The method's prevision and reliability make it a valuable tool in safeguarding ecosystems and assessing the impact of human activities on natural water ...
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.
Other examples are phenolphthalein and thymolphthalein, colorless in acidic to neutral pH, but becoming pink and blue in alkaline environment. Other example are many redox indicators, which undergo reversible color change between colored and colorless form at a specific electrode potential.