An acid-base indicator:

An acid-base indicator is a substance that is used to determine whether a solution is acidic or basic by changing its color. It is a chemical compound that undergoes a color change when exposed to acidic or basic conditions. The change in color is due to the different chemical structures of the indicator in acidic and basic environments. Indicators are commonly used in various fields, including chemistry, biology, and medicine.

Example of an acid-base indicator:

One of the most well-known acid-base indicators is litmus paper. Litmus paper is made by treating paper with a natural dye extracted from lichens. It comes in two forms: blue litmus paper and red litmus paper.

- Blue litmus paper: Blue litmus paper is used to test for the presence of an acid. When blue litmus paper is dipped into an acidic solution, it turns red. This change in color occurs because the acidic solution donates hydrogen ions (H+) to the litmus paper, causing the litmus dye to undergo a chemical change and appear red.

- Red litmus paper: Red litmus paper, on the other hand, is used to test for the presence of a base. When red litmus paper is dipped into a basic solution, it remains red. This is because the basic solution accepts hydrogen ions from the litmus paper, causing no change in the color of the dye.

The use of litmus paper as an indicator is simple, quick, and inexpensive, which makes it widely used in laboratories, classrooms, and even at home. It provides a visual indication of the nature of a solution, allowing individuals to easily determine whether a substance is acidic or basic.

In addition to litmus paper, there are many other acid-base indicators available, such as phenolphthalein, bromothymol blue, and methyl orange. Each indicator has its own range of pH values over which it changes color, making them suitable for different applications.

China rose, Litmus paper indicator .