the ionization constant Ka of an indicator Hln, he color of the unionized form is red and the color of the ionized form is yellow. What is the color of the indicator in a solution whose pH is 4.00? (Hint: the color of an indicator can be estimated by considering the ratio of [HIn]/[In]. If the ratio is equal to or greater than 10, the color will bet hat of the unionized form. If the ratio is equal to or smaller than 0.1, the color will be that of the ionized form.

Question

the ionization constant Ka of an indicator Hln, he color of the unionized form is red and the color of the ionized form is yellow.  What is the color of the indicator in a solution whose pH is 4.00? (Hint: the color of an indicator can be estimated by considering the ratio of [HIn]/[In].  If the ratio is equal to or greater than 10, the color will bet hat of the unionized form.  If the ratio is equal to or smaller than 0.1, the color will be that of the ionized form.

aaronq · Answer

use the henderson-hasselbalch equation

$pH=pKa-log\dfrac{[HIn]}{[In^-]}$

anonymous · Answer

how can i use it if i only know is the pH
?

aaronq · Answer

you also need to know the pKa, there's no way around it

abb0t · Answer

You can rearrange to solve for pKa.

aaronq · Answer

can't though, the ratio of the species is not given at that pH.