A 0.581 g sample of a diprotic acid with a molar mass of 255.8 g/mol is dissolve

Question

A 0.581 g sample of a diprotic acid with a molar mass of 255.8 g/mol is dissolved in water to a total volume of 29.0 mL. The solution is then titrated with a saturated calcium hydroxide solution.

In Part A, it asked to solve for the volumes of added base for the 1st and second equivalence: 108 mL and 216 mL, respectively. I understood that.

My problem was part B in which it asked: The pH after adding 29.0 mLof the base was 3.82. Find the value of pKa1. I used up all my attempts but the answer is supposed to be 4.09. Can someone show me how to get this value.

I used good ole Henderson-Hasselbalch

pH = pka1 + log ([base]/[acid]) where 3.82 is the pH. I guess my problem is getting the the equilibrium moles for the base and acid. Once I have that I know I can easily solve for pka1.

Explanation / Answer

itx too difficult to ans such a long question,i think u must isolate it and then ask,a suitable ans wil b provided ..

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