Harris QCA 8e Chapter 15

1. A standard I2 solution can be made by reaction KIO3 with excess KI in a strongly acidic solution: IO3- + I-3I2 + 3H2O. The species being reduced is
(a) IO3-
(b) I-
(c) H+

2. KMnO4 can be standardized by titration against primary standard sodium oxalate in a strongly acidic solution. The balanced equation for the titration reaction is
(a) 2MnO4- + 8H+ + 3C2O42-2MnO2 + 6CO2 + 4H2O.
(b) 2MnO4- + 16H+ + 5C2O42-2Mn2+ + 5CO2 + 8H2O.
(c) 2MnO4- +16H+ + 5C2O42-2Mn2+ + 10CO2 + 8H2O.

3. KMnO4 is used as the titrant in a potentiometric titration of tin(II) to tin(IV), using a S.C.E. reference electrode. Before the equivalence point, you would calculate the cell voltage using the potentials of
(a) the MnO4-/Mn2+ couple and the S.C.E.
(b) the Sn4+/Sn2+ couple and the S.C.E.
(c) the MnO4-/Mn2+ couple and the Sn4+/Sn2+ couple.

4. KMnO4 is used as the titrant in a potentiometric titration of tin(II) to tin(IV), using a S.C.E.reference electrode. After the equivalence point, you would calculate the cell voltage using the potentials of
(a) the MnO4-/Mn2+ couple and the S.C.E.
(b) the Sn4+/Sn2+ couple and the S.C.E.
(c) the MnO4-/Mn2+ couple and the Sn4+/Sn2+ couple:

5. KMnO4 is used as the titrant in a potentiometric titration of tin(II) to tin(IV), using a S.C.E. reference electrode. The potential of the indicator electrode at the equivalence point would be calculated as
(a) 7E+ = 5Eo(MnO4-/Mn2+) + 2E</I.o(Sn4+/Sn2+).
(b) 7E+ = 2Eo(MnO4-/Mn2+) + 5Eo(Sn4+/Sn2+).
(c) 7E+ = 5Eo(MnO4-/Mn2+) + 2Eo(Sn4+/Sn2+) + 0.05916 log[H+]8.

6. Given the following data, select the best indicator for the titration of iron(II) with thallium(III), using a S.C.E. reference electrode.

(a) Methylene blue
(b) Diphenylamine sulfonic acid
(c) Diphenylamine

7. Which of the following represents a disproportionation?
(a) Cu2+ + Cu(s)2Cu+
(b) IO3- + 8I- + 6 H+3I3- + 3 H2O
(c) 2H2O22H2O + O2(g)

8. A student wants a standard iodine solution. Which of the following procedures would not be correct?
(a) Prepare the standard solution directly from a known weight of iodine dissolved in a known volume.
(b) Make an approximate solution and standardize it against As4O6.
(c) React a known quantity of KIO3 with a small excess of I- and dilute to a known volume.

9. Which of the following titrants would give the sharpest change in voltage (i.e., the steepest titration curve) for a given analyte?
(a) MnO4-
(b) I3-
(c) Cr2O72-

10. Which of the following titrations would give a titration curve symmetric around the equivalence point?
(a) Na2S2O3 titrated with I2.
(b) Ascorbic acid titrated with I2.
(c) As4O6 titrated with I2.

11. A Jones Reductor is used to adjust the oxidation state of the analyte before it is titrated. An example of this use would be
(a) the conversion of Mn2+ to MnO4- to be titrated with standard Fe2+.
(b) the reduction of Fe3+ to Fe2+ to be titrated with MnO4-.
(c) the addition of stannous chloride (SnCl2) to Fe3+ in hot HCl to reduce the iron to Fe2+.

12. A 20.0 mL solution of 0.00500 M Pb2+ in 1 M HCl was titrated with 0.0200 M Ce4+ to give Pb4+ and Ce3+. What is the equivalence point volume of Ce4+ to be added?
(a) 10 mL
(b) 20 mL
(c) 5 mL

13. A 20.0 mL solution of 0.00500 M Pb2+ in 1 M HCl was titrated with 0.0200 M Ce4+ to give Pb4+ and Ce3+. Which expression is correct for the potential of the indicator electrode at the equivalence point? Eo for Ce4+/Ce3+ = 1.47 V and Eo for Pb4+/Pb2+ = 0.139 V.
(a) 2Ec = 1.609 V - 0.059log([Pb2+][Ce3+]/[Ce4+][Pb4+])
(b) 3Ec = 1.748 V - 0.059log([Pb2+][Ce3+]/[Ce4+][Pb4+])
(c) 3Ec = 1.609 V - 0.059log([Pb2+][Ce3+]/[Ce4+][Pb4+])

14. A 20.0 mL solution of 0.00500 M Pb2+ in 1 M HCl was titrated with 0.0200 M Ce4+ to give Pb4+ and Ce3+. What are the correct concentration relationships at the equivalence point?
(a) [Pb4+] = [Ce3+] and [Pb2+] = [Ce4+]
(b) ½[Pb4+] = [Ce3+] and ½[Pb2+] = [Ce4+]
(c) [Pb4+] = ½[Ce3+] and [Pb2+] = ½[Ce4+]

15. A 20.0 mL solution of 0.00500 M Pb2+ in 1 M HCl was titrated with 0.0200 M Ce4+ to give Pb4+ and Ce3+. Calculate the cell potential versus a S.C.E. at the equivalence point? E° for Ce4+/Ce3+ = 1.47 V and E° for Pb4+/Pb2+ = 0.139 V.
(a) 1.507 V
(b) 0.583 V
(c) 0.342 V

16. If you are titrating a mixture of tin(II) and platinum with a Ce4+ solution, which species will be oxidized first? E° for Ce4+/Ce3+ = 1.47 V, E° for Pt2+/Pt = 1.18 V, and E° for Sn4+/Sn2+ = 0.139 V.
(a) Sn4+
(b) Sn2+
(c) Pt