An acid-base indicator has `K_(a) = 10^(-5)`. The acid form of the indicator is red and basic form is blue. Which of the following is//are correct?

Options

A. At `pH = 4.52` solution is red
B. At `pH = 5.47` solution is red
C. At `pH = 6` solution is `75%` red.
D. At `pH = 8` solution is `75%` blue.

Answer

A, B

Explanation

`underset("Red")(HIn)hArrunderset("Blue")(Ind^(T))+H^(o+)(pK_(a) = 5)`
A. When `pH lt pK_(a) (4.52 lt 5)`, colour of acid form i.e., red predominates.
B. When `pH gt pK_(a) (5.47 gt 5)` , colour of basic form, i.e., blue predominates.
C. `75%` red `rArr [(In^(T))/(HIn)] = (0.75)/(0.25)`
`rArr pH = 5 + "log" 3 = 5 + 0.48 = 5.48` (Hence (C) is wrong)
D. it is also wrong statement.