Question

A solution of 0.207 M aspartic acid, the charge neutral form of the amino acid, is titrated with 0.0690 M NaOH . The pKa values for aspartic acid are 1.990 , 3.900 , and 10.002 , corresponding to the α-carboxylic acid group, the β-carboxylic acid group, and the amino group, respectively. Calculate the pH at the first equivalence point of this titration.

Answer 1

Answer:

pH = 6,951

Explanation:

The neutral form of aspartic acid is in its isolectric point. For aspartic acid the isoelectric point is the average of pka1 and pka2, thus:

$pH =\frac{1}{2} (3,900+1,990)$= 2,945

The addition of stoichiometric amounts of NaOH at the first equivalence point will increase the pH at average of pka2 and pka3 thus:

$pH = \frac{1}{2} (3,900+10,002)$= 6,951

Thus, pH at the first equivalence point is 6,951

I hope it helps!