Untitled - Kelly Walsh High School

278 CHEMISTRY FOR THE UTTERLY CONFUSED
place, while the cathode is the electrode at which reduction takes place. The cell
notation is a short-hand way of representing an electrochemical cell. The standard
reduction potentials are voltages associated with a reduction half-reaction,
relative to the standard hydrogen electrode (SHE). These reduction potentials
may be used to calculate the cell voltage. We can use the Nernst equation to calculate
the cell voltage under nonstandard conditions.
1. Define oxidation and reduction.
2. Assign oxidation numbers to each element in each of the following substances.
a. H 2O b. Na 2SO 4 c. FeCl 3 d. K 2O 2 e. CaCr 2O 7
3. a. What is the sign of the anode in a Galvanic cell?
b. What is the sign of the anode in an Electrolytic cell?
4. a. In a Galvanic cell, reduction occurs at which electrode?
b. In an Electrolytic cell, reduction occurs at which electrode?
5. What happens to the oxidizing agent during a redox reaction?
6. What is a faraday?
7. Balance the following half-reactions:
a. 2 e Cl 2 l _____
b. 3 e CrO 4 2 4 H2O l _____ 8 OH
c. _____ FeO 4 2 8 H l Fe 3 4 H2O
d. Pb 4 _____ l Pb 2
e. S 2 2 l 2 S _____
8. Balance the following redox equations:
a. S 2 (aq) Cr 2O 7 2 (aq) H (aq) l S(s) Cr 3 (aq) H2O(l)
b. Cl 2(g) H 2O(l) SO 2(g) l SO 4 2 (aq) Cl (aq) H (aq)
c. Mn 2 (aq) PbO 2(s) H (aq) l MnO 4 (aq) Pb 2 (aq) H2O(l)
d. SnO 2 2 (aq) Bi 3 (aq) OH (aq) l SnO3 2 (aq) Bi(s) H2O(l)
e. ClO 2 (aq) MnO4 (aq) l MnO2(s) ClO 4 (aq) (basic)
9. Metallic magnesium can be made by the electrolysis of molten MgCl 2.
What mass of Mg is formed by passing a current of 3.50 A through molten
MgCl 2 for a period of 550 min?
10. Use standard electrode potentials to calculate E cell for the disproportionation
of copper(I) ion: 2 Cu (aq) l Cu(s) Cu 2 (aq). The standard reduction
potentials are:
Cu (aq) 1 e l Cu(s) E 0.52 V Cu 2 (aq) 1 e l Cu(s)
E 0.15 V
11. Calculate E cell for the reaction in question 10 if [Cu ] 0.25 M and [Cu 2 ]
1.50 M.
12. Using the reduction potentials given in this chapter and the following halfreaction:
I 2(s) 2 e l 2 I (aq) E 0.53 V, write the balanced chemical
equation for the electrolysis of a potassium iodide, KI, solution.