Question

What is the net charge of glycine found in a solution with pH=4 (pK1=2.35 for carboxyl group, pK2=9.78 for amino group)?

A) -2
B) -1
C) 0
D) +1

Answer 1

C) 0

At pH 4, glycine has a carboxyl group with a negative charge and an amino group with a positive charge, which cancel each other out, resulting in a net charge of zero.

Step-by-step explanation:

The net charge of glycine in a solution with a pH of 4 can be determined by considering the pKa values of the functional groups in glycine and the pH of the solution. Glycine has a carboxyl group with a pKa of 2.35 and an amino group with a pKa of 9.78.

At pH 4, which is higher than the pKa of the carboxyl group and lower than the pKa of the amino group, the carboxyl group will be deprotonated and carry a negative charge, while the amino group will be protonated and carry a positive charge.

Therefore, the net charge on glycine at pH 4 will be zero, because the positive and negative charges will cancel each other out.