Ascorbic acid is a weak organic acid also known as vitamin C. A student prepares a 0.20 mol/L aqueous solution of ascorbic acid and measures its pH as 2.40. Based on this evidence, what is the Ka of ascorbic acid?

Question

DrBob222 · Answer

Based on what I can find on the internet, ascorbic acid is a monoprotic acid. If that is so, then let's call ascorbic acid HC.
Then HC ==> H^+ + C^-

Ka = ((H^+)(C^-)/(HC)
If pH = 2.40, then (H^+) = 0.00398/
(C^-) is the same.
(HC) = 0.2 = 0.00398
Plug in the Ka expression and solve for Ka. I get a little over 8 x 10^-5 which gives a pKa of 4.09 which isn't far from the pKa listed in my quant book of 4.17.

Bradley · Answer

Thank you! Umm...Whats a quant book? A book read by extraterrestrials??:P

~christina~ · Answer

Quantitative analysis chemistry book