PH Indicators And PH Paper

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What does a pH indicators do?

How does it indicate a pH?

Why does a pH indicator changes colors?

For example, the endpoint of the specific pH indicator is pH = 5.0, and the indicator changes from red ("acid form" color) to green ("base form" color). If I have a solution with this pH indicator in it and the initial pH is 2.0, then the solution is red. If I increase the pH, the solution will stay red until pH of 4.0 where it will start changing from a "pure" red to a mix of red and green until pH = 6.0 where the solution will be "pure" green. The solution will stay green for all pH above 6.0.

So, each pH indicator "changes" color at a different pH point (or more specifically range). So the pH indicator shows that the solution has "gone" thru that pH (called endpoint). As the following link shows most pH indicators (and their endpoints and the color changes) are not at a pH of 7.0. So not all pH indicator will determine if the solution is acidic (solution pH less than 7.0), neutral (solution pH of 7.0) or basic (solution pH of greater than 7.0). They will however, show if you are at a specific pH range.

For more details on pH Indicators, click here [AP Chem pH Indicator Additional Information]

Actual pH Indicator and pH paper

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Last edited December 12, 2015 10:05 am (diff)