For the value solution in the previous question if the pH we

For the value solution in the previous question, if the pH were adjusted to 9.0 (at constant volume), the average charge of an amino group would be about:

Solution

the charge on the amino acids could be calculated in the following way:

if the pH< pKa, then it results in protonation

and if pH>pKa then it results in deprotonation.

so we need to see the pKa values of the three groups present in valine :

the carboxyl group, the amino group and the side chain,

since the question asks only for the charge of amino group ,

the pKa of amino group is 9.72,

since pH< pka, it would result in protonation of the amino group, and therefore the charge would be +1.