The acid from of an acid base indicator is yellow in acid and red in basic from. What is the change in `pH` in order to change the indicator form `80%` yellow to `80%` red.

Answer

A, B

Explanation

`{:(,HInhArr,H^(o+)+,Ind^(Theta),),(,"Acid form",,"Base form",),("First case:",80%"yellow",,20%red,),("Second case:",20%yellow,,80%red,):}`
First case:
a. `pH_(1) = pK_(a) + "log" ([In^(Theta)])/(["Hin"])`
`= pK_(a) + log ((20)/(80)) …(i)`
` = pK_(a) + log 1//4`
Second case:
b. `pH_(2) = pK_(a) + log ((80)/(20))`
`= pk_(a) + log 4 ...(ii)`
From equations (i) and (ii), we get
`pH_(2) - pH_(1) = 2 log 4 = 4 log 2 = 4 xx 0.3 = 1.2`