[London]

The indicator Bromothymol Blue (pKa 6. is added to a Solution with pH 7.1.

The ratio of salt/acid (conjugate base/acid) can be worked out from the difference between pH and pKa i.e 7.1 minus 6.8 = 0.3.

My question is HOW does the difference between pH of one Solution and pKA of another solutuion equate to the salt/acid ratio? If the answer concerns the henderson -hasslbach equation, then i thought this equation is only applicable to the pH and pKa of the SAME solution or the same indicator. But this question relates to pH and pKa of two different solutions. Please help.


 Someone else on a different forum gave me the answer "The anion of the indicator (conjugate base) is its "salt". There is no confusion"

but i already know this, and i dont see how it helps with my question


Ps. Soz if i posted this on the wrong forum (im new), and i cant seem to find any forums for college level questions

[Borek]

You add small amount of indicator to a large amount of solution - you can safely assume pH of the mixture didn't change and is still 7.1, hence you can use pH of 7.1 and pKa of 6.8 at the same time.