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There are different pH indicators that can be used in analysis. The change in the color determines the change in the pH of the solution. For example, phenolphthalein changes from colorless to fuchsia pink. The different kinds of indicators have different kinds of pH ranges. Meaning, they change color at different pHs. We need different indicators for different pH ranges in order to determine the relative pH of the solution most probably for unknown samples.
For example your teacher gave an unknown solution and you have to determine the relative pH of the solution. If you only use phenolphthalein with a pH range of 8.3-10.0, you can only determine if the pH is above or below that level. You need other indicators to determine other pH ranges. Like for example, the Bromocresol green indicator have a color change at pH 3.8-5.4.
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