Acid-Base Indicators: Colorful Signals for pH Changes

Study Notes

Acid-Base Indicators: Colorful Signals for pH Changes

Acid-base indicators are compounds that change color at a specific pH range, which can be used to determine the pH of a solution. These indicators are typically weak organic acids or bases, and their color changes correspond to deprotonation or protonation of the indicator molecule.

Color Changes and pH Ranges

Acid-base indicators exhibit color changes due to the conversion of one tautomeric form to another, which is dependent on the pH of the medium. For example, phenolphthalein is colorless in any aqueous solution with a hydronium ion concentration greater than 5.0 × 10−9 M (pH > 8.3), but red or pink in more basic solutions where the hydronium ion concentration is less than 5.0 × 10−9 M (pH > 8.3).

Selection of Indicators for Titrations

When choosing an indicator for a titration, it is essential to consider the pH range of the indicator and the pH change of the reaction. For example, in the titration of a strong acid with a strong base, the pH quickly changes, so an indicator with a broad pH range, such as phenolphthalein (pH 8-10), can be used.

pH Testing

Acid-base indicators are also used for pH testing, such as with litmus paper, which contains indicators that change color in response to the pH of a solution. For example, red litmus paper turns blue in the presence of a base, and blue litmus paper turns red in the presence of an acid.

Natural Indicators

Natural indicators can be obtained from various plant parts like flowers, fruits, and leaves, which have been found to have comparable properties to synthetic indicators. These natural indicators have been proposed as alternatives to synthetic indicators due to their potential advantages, such as being less expensive, more readily available, and having lower environmental impact.

In conclusion, acid-base indicators play a crucial role in determining the pH of a solution and are essential for titration and pH testing applications. By understanding the pH ranges and color changes of various indicators, chemists can effectively select and use the appropriate indicator for their specific needs.

Description

Explore the world of acid-base indicators, compounds that change color at specific pH ranges to determine the acidity or basicity of a solution. Learn about the color changes, pH ranges, selection criteria for titrations, pH testing methods, and the use of natural indicators as alternatives.

Acid-Base Indicators: Colorful Signals for pH Changes

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Questions and Answers

Dans quel cas serait-il préférable d'utiliser de la phénolphtaléine comme indicateur lors d'une titration ?

Quelle est la principale cause du changement de couleur des indicateurs acido-basiques ?

Quel type de composés sont généralement les indicateurs acido-basiques ?

Dans quelle gamme de pH la phénolphtaléine est-elle colorée en rouge ou rose ?

Quelle est la raison pour laquelle les indicateurs acido-basiques changent de couleur ?

Quelle est la caractéristique principale des indicateurs acido-basiques utilisés pour le test du pH ?

Comment réagit du papier tournesol rouge en présence d'une base ?

Quelle est l'utilité principale des indicateurs acido-basiques dans les titrations ?

Quel est l'effet de l'augmentation de la concentration en ions hydronium sur la couleur de la phénolphtaléine ?

Quelle est la caractéristique commune des indicateurs acido-basiques adaptés aux titrations ?

Study Notes