Which of the following is true about indicators? A. They are weak acids or bases. B. They are...

Question:

pH Indicators:

How do you know when a reaction has gone to completion? For acids-base reactions, you can use a pH probe to test the pH. But, those don't give much of a visual indication, and if you don't have one available, then you need to find another strategy. One alternative is a pH indicator, like phenolphthalein. These are molecules that change color dramatically at a certain pH. For phenolphthalein, at pHs lower than 8, they exist in their protonated form, which is colorless. At higher pH, they lose their proton and turn the solution a deep purple color. This makes it a good indicator for reactions with an equivalence point near the 7-10 pH range. The point where an indicator changes color is called the end-point, and it can serve as an approximation for the equivalence point of a titration.

Answer and Explanation: 1