Acid-base indicator

Acid-Base Indicator

An acid-base indicator is a chemical compound that changes color when it comes into contact with an acid or a base. These indicators are often used in laboratory settings to determine the pH of a solution, which is a measure of its acidity or alkalinity.

History

The concept of acid-base indicators dates back to the late 19th century, when scientists first began to understand the nature of acids and bases. The first indicators were simple organic compounds that changed color in response to changes in pH.

Function

Acid-base indicators function by undergoing a chemical reaction when they come into contact with an acid or a base. This reaction causes the indicator to change color, providing a visual indication of the pH of the solution.

Types of Indicators

There are many different types of acid-base indicators, each with its own unique color change range. Some of the most commonly used indicators include litmus, phenolphthalein, and bromothymol blue.

Litmus

Litmus is a natural dye extracted from certain lichen species. It turns red in acidic solutions and blue in basic solutions.

Phenolphthalein

Phenolphthalein is a synthetic indicator that is colorless in acidic solutions and pink in basic solutions.

Bromothymol Blue

Bromothymol blue is another synthetic indicator. It turns yellow in acidic solutions, green in neutral solutions, and blue in basic solutions.

Applications

Acid-base indicators are widely used in a variety of applications. They are commonly used in laboratories for pH testing, but they also have applications in medicine, environmental science, and industry.

See Also

• pH
• Acid
• Base (chemistry)
• Chemical reaction