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lilavasa [31]
2 years ago
11

The indicator propyl red has ka = 3.3 × 10–6 . estimate the approximate ph range over which this indicator would change color.

Chemistry
1 answer:
ollegr [7]2 years ago
7 0
We let the chemical equation for the weak acid indicator propyl red HPr be
     HPr + H2O ↔ H3O+ + Pr-
Therefore, the acid dissociation constant Ka is
     Ka = [H3O+][Pr-] / [HPr]
The color of this indicator turns from red to yellow or the other way around at its turning point at which 
     [HPr] = [Pr-]
Substituting this to the equation for Ka, we now have
     Ka = [H3O+]
The pH of the solution at its turning point is 
     pH = -log[H3O+] = -log(Ka) = -log 3.3×10^-6 = 5.48
<span>On this account, the pH range is pH 5.0 to 6.0.</span>
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We are also given that:
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