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Acid-base indicators are either weak organic acids or weak organic bases. Indicators change colour in dilute solution when the hydronium ion concentration reaches a particular value. For example, phenolphthalein is a colourless substance in any aqueous solution with pH less than 8.3. In between thep H range 8.3 to 10 , transition of colour(colourless to pink) takes place and if p H of solution is greater than 10 solution is dark pink. Considering an acid indicator HIn, the equilibrium involving it and it's conjugate base(In') can be represented as:
⇌ H + +
p H of solution can be computed as: p H = p K ln + log
In general, transition of colour takes place in between thep H range, p K ln ± 1 .
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Acid-base indicators are either weak organic acids or weak organic bases. Indicators change colour in dilute solution when the hydronium ion concentration reaches a particular value. For example, phenolphthalein is a colourless substance in any aqueous solution with pH less than 8.3. In between the
In general, transition of colour takes place in between the
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