a First do the calculation by assuming that the concentrations of HA and A- equal their formal concentrations.. b Then, do the calculation, using the real values of [HA] and [A-] in the
Trang 1Analytical chemistry
Semester II, 2020-2021
1
HOMEWORK # 2 Due date: 1/4/2021
1 (20 pts) The base B has pKb = 5.00
(a) What is the value of pKa for the acid BH+?
(b) At what pH is [BH+] =[B]?
(c) Which is the principal species at pH 7.00: B or BH+?
(d) What is the quotient [B]/[BH+] at pH 12.00?
2 (40 pts) Calculate the pH of a solution prepared by mixing 0.0800 mol of chloroacetic acid (ClCH2COOH) with a pKa = 2.86, plus 0.0400 mol of sodium chloroacetate (ClCH2COO –Na+) in 1.00 L of water
(a) First do the calculation by assuming that the concentrations of HA and A- equal their formal concentrations
(b) Then, do the calculation, using the real values of [HA] and [A-] in the solution by assuming that at equilibrium, [OH-] << [H3O+] or the solution is acidic
3 (40 pts.) A weak acid (pKa = 5.00) was titrated with 1.00 M KOH The acid solution had a volume of 100.0 mL and a molarity of 0.100 M Find the pH at the following volumes of base added Vb = 0; 5.00; 10.0; and 12.0 mL Sketch the titration curve