Asked by George

The ionization constant Ka of an indicator HIn is 1.0x10^-6. The color of the nonionized form is red and that of the ionized form is yellow. What is the color of this indicator in a solution whose pH is 4.00?

Thanks!

Answers

Answered by DrBob222
K<sub>HIn</sub> = (H^+)(In^-)/(HIn) = 1E-6

Solve for (In^-)/(HIn) = Ka/(H^+) =
1E-6/1E-4 = 1E-2 = 0.01
(HIn)(red) = 100(In^-)(yellow)
So what color is it?
Check my thinking.
Answered by George
would it be orange?
Answered by George
Is it because it is more acidic?
Answered by George
in my text book it says that if the calculated value is less than or equal to 0.1 then the color of the conjugate base (In- in this case) predominates. does this mean that the solution will be yellow then?
Answered by DrBob222
Covered under later listings.
Answered by Benny
the ratio of Hln:ln- is 100:1, much greater than 10, therefore it will be yellow
Answered by Benny
Disregard what I said yesterday, it was incorrect. The ratio of is correct, but that actually means it will be red, because the acid predominates (not enough ionization to change the color)
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