Chemistry Practice Problems Acid Base Indicators Practice Problems Solution: Effect of cations on solution pH.The pH values of ...

Solution: Effect of cations on solution pH.The pH values of 1.0 M solutions of four nitrate salts are estimated using acid-base indicators.Why do we need to use multiple acid-base indicators in this figure?

Problem


A photograph shows beakers of different colors at different pHs. Beaker one contains a dark green solution of sodium nitrate and the indicator bromthymol blue at pH 7.0.  Beaker two contains a light green solution of calcium nitrate and the indicator bromthymol blue at pH 6.9.  Beaker three contains a yellow solution of zinc nitrate and the indicator methyl red at pH 5.5.  Beaker four contains a red solution of aluminium nitrate and the indicator methyl red at pH 3.5.
Effect of cations on solution pH.
The pH values of 1.0 M solutions of four nitrate salts are estimated using acid-base indicators.

Why do we need to use multiple acid-base indicators in this figure?

Solution

We have to determine why is there a need to use multiple pH indicators to determine the pH of different solutions.

Indicators are weak acids/bases. The pH at which an indicator changes color is determined by its pKIn value.


An indicator has different colors above and below its pKIn value.

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