Supplemental Instruction
Iowa State University / Leader: / Olivia
Course: / CHEM 178
Instructor: / Bonaccorsi
Date:
T/F A reductant, or reducing agent, is reduced in a chemical reaction.
1. Indicate whether the following balanced equations involve oxidation-reduction. If they do, identify the elements that undergo changes in oxidation number.
a. PBr3(l) + 3H2O(l) à H3PO3(aq) + 3HBr (aq)
b. NaI (aq) + 3HOCl (aq) à NaIO (aq) + 3HCl (aq)
c. 3SO2 (g) + 2HNO3 (aq) + 2H2O (l) à 3H2SO4(aq) + 2NO (g)
d. 2H2SO4 (aq) + 2NaBr (s) à Br2 (l) + SO2 (g) + Na2SO4 (aq) + 2H2O (l)
2. Complete and balance the following equations in acidic solution, and identify the oxidizing and reducing agents.
a. NO2- (aq) + Cr2O72- (aq) à Cr3+ (aq) NO3- (aq)
b. Cr2O72- (aq) + CH3OH (aq) à HCO2H (aq) + Cr3+ (aq)
3. Given the following data:
Fe2+ + 2e- à Fe Eored = -0.44 V
Ag+ + e- à Ag Eored = 0.80 V
Answer the following questions with respect to the reaction
Fe2+ (aq) + 2Ag (s) à Fe (s) + 2Ag+ (aq)
a. What is E0 for the reaction?
b. Is the reaction spontaneous at standard state conditions?
c. What is the value of E at equilibrium?
4. Metallic Mg can be made by the electrolysis of molten MgCl2
a. What is the mass of Mg formed by passing a current of 4.55 A through Molten MgCl2 for 4.5 days?
b. How many minutes are needed to plate out 25.00g of Mg from molten MgCl2 using 3.5 A of current?
5. A voltaic cell is constructed of one half cell consisting of an aluminum strip placed in a solution of Al(NO3)3, and the other has a nickel strip placed in a solution of NiSO4. The overall cell reaction is 2Al (s) + 3Ni2+ (aq) à 2Al3+ (aq) + 3Ni (s)
a. What is being oxidized and reduced?
b. Write the half reactions that occur for the two half cells.
c. Which electrode is the anode? Which is the cathode?
d. Which way do the electrons flow?
6. Find the cell potentialof a galvanic cell based on the following reduction half-reactions at 25 °C
Cd2++ 2 e-→ Cd E0= -0.403 V
Pb2++ 2 e-→ Pb E0= -0.126 V
where [Cd2+] = 0.020 M and [Pb2+] = 0.200 M.
7. Consider a galvanic cell that uses the reaction:
Cu(s) + 2Fe3+(aq) → Cu2+(aq) + 2Fe2+(aq)
What is the potential of a cell at 25 °C that has the following ion concentrations?
[Fe3+] = 1.0 x 10-4 M [Cu2+] = 0.25 M [Fe2+] = 0.20 M
What is Q, reaction quotient?
8. Label the voltaic cell: Zn/Cu
Cathode, anode, salt bridge, electron flow, reduction, oxidation, flow of electrons, flow of anions, flow of cations, which side’s metal strip gains/loses mass, half reactions
9. Label the electrolytic cell: Zn/Cu
Cathode, anode, salt bridge, electron flow, reduction, oxidation, flow of electrons, flow of anions, flow of cations, which side’s metal strip gains/loses mass, half reactions
10. Calculate E°cell, Ecell, andG for the following cell reaction.
3Zn(s) + 2Cr3+(0.0010 M)3Zn2+(0.010 M) + 2Cr(s)
E°cell =
Ecell =
ΔG =
11. Calculate the standard reaction entropies for the following reactions using standard molar entropies.
2 SO2 (g) + O2 (g) à 2 SO3 (g)
SO3(g) + H2O (l) à H2SO4 (aq)
S (g) + O2 (g) à SO2 (g)
An endothermic reaction has ΔH = 60. kJ and ΔS = −120. J/K. Assuming that ΔH and ΔS do not vary with temperature, at what temperature will the system be at equilibrium?