Question

(b) The amino acid lysine has the following values of pK : PK1 =2.2, pK2 = 8.9, PKR = 10.5 (the pK, of the amino group in the side chain). At pH 7 it has the structure shown below (6). Draw the structure that you would expect for lysine at pH 9.7, indicating the charges as appropriate. HZN 0 HINA (2 marks) (c) Phenol (C6H5OH) and 2,4,6-trichlorophenol (C6H2C13OH) are both weak acids with pK, values of 9.89 and 6.21, respectively, at 298.15 K. (i) Write down the dissociation reaction and corresponding expression for the equilibrium constant for 2,4,6-trichlorophenol. What is the conjugate base of this acid? (3 marks) (ii) Which of these two acids is the stronger? Considering the difference in electron density of the OH group in each molecule and the effect that this will have on the acidic hydrogen, suggest a reason for the difference in the strength of the two acids. (3 marks)

Answer 1

SOLN B

if pH < pKa then all the ionizable NH2 group will be protonated as NH3+

if pH > pKa then all the ionizable COOH group will be de-protonated as COO-

so at pH 9.7 the predominant form of lysine is

H2N pKa : 10.5 O pka : 2.2 NH3* pKa : 8.9

According to HOMEWORKLIB POLICY only 1 question per post is allowed. please post the rest question seperately.

PLEASE LEAVE THE POSITIVE FEEDBACK IF YOU LIKE THE SOLUTION