Acid-base indicators are important because they help chemists get an estimate of the pH value of a given substance. These indicators can be used to classify substances as acids or bases, which are two important classifications in the world of chemistry. Acid-base indicators are usually weak acids or bases and are able to respond to changes in the hydrogen ion concentration of an unknown substance.
The pH scale measures how acidic or basic a given chemical is, according to About.com. Chemicals that are extremely acidic or basic are considered reactive, which means they can be highly volatile, according to the Environmental Protection Agency. People who are exposed to highly acidic or basic chemicals can be burned, injured or even killed. For this reason, the classifying of a substance as either acidic or basic, by getting an estimate of its place on the pH scale, is important. Acid-base indicators are a spectrum of different tools and instruments that can help make this classification.
Acid-base indicators are similar to dyes. When exposed to chemicals that have different pH values, the color of the indicator changes accordingly. Acid-base indicators often come in the form of litmus papers, which change color depending on whether they are submerged in an acidic or basic substance, according to UC Davis' ChemWiki.