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 blue.
C. At `pH =6`, solution is `75%` red
D. At `pH = 8`, solution is `75%` blue.

Answer

A, B

Explanation

`{:(HIn,hArr,Ind^(Theta),+,H^(o+)(pK_(a)=5)),(Red,,Blue,,):}`
a. When `pH lt pK_(a) (4.52 lt 5)`, colout of acid from i.e., red predominates.
b. When `pH gt pK_(a) (5.47 gt 5)`, colour of basic from i.e., blue predominates.
c. `75% red rArr [(In^(Theta))/(HIn)] = (0.75)/(0.25)`
`rArr pH = 5+ log 3 = 5 + 0.48 = 5.48` (Hence (c) is wrong)