Question

the pKa of the carboxylic acid group of the amino acid glycine is 2.35. The pKa for acetic acid is 4.76. how many more times better is the carboxylic acid of the glycine than the carboxylic acid of acetic acid?

Answer 1

ANSWER.Given that pKa1 of carboxylic acid group of glycine =2.35 , pKa2 for acetic acid = 4.76. pKa is defined as measure of the strength of an acid,if the acid ionises completely (high acid strength) then Ka will be larger and thus pKa will be small.

pKa1 = -logKa1 =2.35 logKa1=-2.35 Ka1=10^-2.35=10^-3x10^0.65=4.47x10^-3 M

pKa2 =-logKa2 =4.76 logKa2 =-4.76 Ka2 =10^-4.76=10^-5x10^0.24=0.53x10^-5 M.

strength of acid 1/strength of acid 2=4.47x10^-3 M/0.53x10^-5 M.=8.43x10²10x2.929.

so, carboxylic acid of of glycine is almost 29 times stronger than the carboxylic acid of acetic acid.