A beaker of 1.00 M acid and a beaker of 1.00 M base look identical - two beakers of clear liquid that look the same but have very different properties. They can be distinguished easily by adding an indicator. Acid−Base indicators are compounds whose colors are sensitive to pH. They are complex molecules that are weak acids. They exhibit one color when the proton is attached and a different color when the proton is absent. This PowerPoint presentation explains how indicators work, and provides a table showing the colors and pH ranges of various indicators. Worksheets on this topic are available free of charge on my website at www.evanschemistrycorner.com.