Harris QCA 8e Chapter 11
1. The reaction of EDTA with a divalent metal ion, such as Cu2+, complexed with
ammonia could be represented as
(a) M(NH3)42++ Y4- = MY2- + 4NH3.
(b) M(NH3)2+ + Y4- =MY2- + NH3.
(c) M(NH4)46+ + Y4- =MY2- + 4NH44+.
2. The reaction of EDTA with a trivalent metal ion at a pH of 4.0 may be written as
(a) M3+ + Y4- =MY-.
(b) M3+ + H2Y2- =MY- + 2 H+.
(c) M3+ + H4Y =MY- + 4 H+.
3. Calculate the conditional formation constant Kf' for the formation of an EDTA
complex with copper(II) at a pH of 5.00, if log Kf = 18.80.
(a) 2.3 x 1012
(b) 7.0 x 10-6
(c) 5.9 x 10-26
4. Fe3+ can be successfully titrated with EDTA in the presence of Ni 2+ by
(a) masking Ni2+ with cyanide and titrating Fe3+ at pH 3.0.
(b) titrating at pH 2.0.
(c) masking Ni 2+ with triethanolamine and titrating Fe3+ at pH 3.0.
5. Which of the following displacement titrations would be feasible?
(a) Ag+ + MgY2- =Mg2+ + AgY3(b) Ba2+ + MgY2- =Mg2+ + BaY2(c) Cu2+ + MgY2- =Mg2+ + CuY26. Given that Kf of CuY2- = 6.3 x 1018 and Kf of MgY2- = 6.2 x 108, calculate the
equilibrium constant for the reaction Cu2+ + MgY2- =Mg2+ + CuY2-.
(a) 1.0 x 1010
(b) 2.1
(c) 9.8 x 10-11
7. Which of the following EDTA titrations would be most complete?
(a) Cu2+ at pH 10
(b) Al3+ at pH 4
(c) Fe3+ at pH 5
8. A beaker containing 50.0 mL of 0.300 M Ca2+ at pH 9 is titrated with 0.150 M
EDTA. The pCa2+ at the equivalence point is
(a) 5.39.
(b) 5.21.
(c) 1.58.
9. A student wishes to use Eriochrome black-T as an indicator for an EDTA titration
of Pb2+, and therefore, must work at a pH of about 10. To adjust the pH, the student
should use
(a) NaOH.
(b) NH3.
(c) NH3 buffer.
10. The equation for the conditional formation constant of an EDTA-metal complex
ion is Kf' = Kf
ay4- = [MYn-4]/[Mn+][Y4-]. The presence in the solution of an auxiliary
complexing agent such as tartrate ion, at a given concentration of Y4- would
(a) have no effect on [MYn-4].
(b) lower [MYn-4].
(c) increase [MYn-4].
11. When is a direct EDTA titration not useful?
(a) When the metal precipitates in the absence of EDTA.
(b) When the metal reacts too quickly with EDTA.
(c) When the metal does not block the indicator.
12. Calculate the pCo2+ after 12.00 mL of 0.03846 M EDTA in the titration of
25.00 mL of 0.020 M Co2+ (Kf = 2.04 x 1016) at pH = 6.00.
(a) 1.04 x 10-3 molar
(b) 4.415
(c) 2.983
13. Calculate the pCo2+ after 13.00 mL of 0.03846 M EDTA in the titration of
25.00 mL of 0.020 M Co2+ (Kf = 2.04 x 1016) at pH = 6.00.
(a) 9.095
(b) 6.723
(c) 1.89 x 10-7 molar
14. Calculate the pCo2+ after 14.00 mL of 0.03846 M EDTA in the titration of 25.00
mL of 0.020 M Co2+ (Kf = 2.04 X 1016) at pH = 6.00.
(a) 10.455
(b) 15.196
(c) 3.51 x 10-11 molar
15. Using your textbook, determine which single-element EDTA titration can be
carried out as described.
(a) Analyze In3+ in the presence of Co2+ and Ni2+ at a pH = 2.50
(b) Analyze Fe3+ in the presence of Al 3+ at a pH = 3.50
(c) Analyze Pb2+ in the presence of In 3+ and Hg2+ at a pH = 8.00