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An indicator has a pK a of 7.5. What is the ratio of the concentration of the base form to the concentration of the acid form ([A - ]/ [HA], in a buffer solution in which the pH is 6.5 ?

Options

  1. A10/1
  2. B1/1
  3. C1/10
  4. D6.5/7.5

Correct answer

C. 1/10

Step-by-step solution

Indicator is weak organic acid HA pH = pK a + log A - HA 6.5 = 7.5 + log A - HA log A - HA = - 1 ∴ A - HA = 0.10

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