If the monoprotic acid HAb has a pK of 5 and a solution is adjusted to pH 8: a)

Question

If the monoprotic acid HAb has a pK of 5 and a solution is adjusted to pH 8: a) what is the concentration of hydrogen ions in that solution? ____ b) what is the ratio of Ab" to HAb? ____ Citric acid, a tri-protic, tri-carboxylic acid has pKs of 3.1,4.8 and 6.4 thus can exist as H_3Cit, H_2Cit^-, HCit^-2 and Cit^-3 a) What would be the dominant form at pH 5.0? _____ b) What would be the second most dominant from at pH 5.0? ____ The following is a teaching laboratory titration curve of a solution containing the amino acid Valine. Draw the structure of the dominant charged form at each arrow:

Explanation / Answer

2. a. we know pH = -log (H+)
So pH = 8

8 = -log (H+)

-8 = log (H+)

1e-8 = (H+)

So, conc of hydrogen ion = 1 x 10^-8M.

2b. We know H-H equation, pH = pKa + log (Ab-/HAb)

So, pH = 8

pKa = 5

So, 8 = 5 +  log (Ab-/HAb)

3 =  log (Ab-/HAb)

1000 =  (Ab-/HAb)

So, ration of AB- to HAb = 1000.

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