How to Find the Ka of an Acid from pH and Titration Data?

AI Thread Summary
To determine the Ka of the acid from the given titration data, the pH of the resulting solution after mixing the neutralized solution and the remaining acid must be analyzed. The pH of 3.35 indicates a concentration of H+ ions, which can be calculated using the formula [H+] = 10^(-pH). The equilibrium expression for the dissociation of the acid, represented as HA ⇌ H+ + A-, can be used to relate the concentrations of HA and A- to Ka. By substituting the known values into the equation, the Ka can be derived. This approach effectively utilizes the relationship between pH, concentrations, and the acid dissociation constant.
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Homework Statement



A solid acid is dissolved in enough water to make 200 mL of a solution. 40.0 mL of the solution is titrated to a phenolphtalein end point with an NaOH solution. The neutralized solution and the remainder of the acid solution are then mixed and the pH of the resulting solution is found to be 3.35. Find the Ka of the acid.by trying to figure out this problem, I assumed that the following formula would come in useful:

((concentration of HA)/(concentration of A-))=volume of acid/volume of base=((concentration of H+)/(Ka))I have attempted this problem, but the equations I had weren't fit for this problem.
 
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After mixing you have a solution containing acid and its conjugate base in known proportions.

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