Indicators as Weak Acids
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Re: Indicators as Weak Acids
I think it's because the release of the H+ from the weak acid results in a structural change. The course reader says it absorbs light differently. Therefore, you need the release of an H+ for the indicator to be effective and that's why they are weak acids.
Re: Indicators as Weak Acids
Indicators can be either weak acids or weak bases. Taking a weak acid as an example, the acid and its conjugate base have different colors. At a low pH, the concentration of H3O+ is high and so equilibrium lies to the left. When at a high pH, the concentration of H3O+ is low and equilibrium lies to the right, so the color will change accordingly. Indicators can't be strong acids/bases because they dissociate completely and reversible equilibrium cannot be introduced so the color won't change.
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