Answer to Question #87354 in General Chemistry for Sydney P

Question

Draw zwitterionic from of leucine with a ph of 6.0

Answer 1

For leucine:

$pK_{a1}=2.36$ (carboxylic group),

$pK_{a2}= 9.60$ (amino group),

$pI = 5.98$

When pH is less than 2.36 both carboxylic and amino groups are protonated (net charge = +1), when pH is between 2.36 and 9.60 only amino group can be protonated (net charge = 0), when pH is more than 9.60 both carboxylic group and amino group are deprotonated (net charge = -1).

pH = 6 lies between 2.36 and 9,60, moreover this value is very close to pI, then zwitterionic form of leucine is :

 

Net cherge = 0