Answer:
2.698
Explanation:
Cysteine + H+ <==> cysteineH+
at the equivalence point
cosidering 1 L of cysteine solution
volume of HNO3 to reach equivalence point = 0.108 M x 1 L/0.0540 M = 2.0 L
[CysteineH+] formed = (0.108 M x 1 L)/(1.0 + 2.0) L = 0.036 M
hydrolysis of salt
cysteineH+ + H_2O <==> cysteine + H_3O+
let x amount hydrolyzed
Ka1 = [cysteine][H3O+]/[cysteineH+]
pKa1 = -log[Ka1] = 1.70
Ka = 0.02
so,
0.02 = x^2/(0.036-x)
x^2 + 0.02x - 0.00072 = 0
x = 0.002
pH at equivalence point = -log(0.002) = 2.698
