CHEM 1474 Test 4 Summer 1997

SHORT ANSWER: 2 points each. Fill in the blank with the most correct answer.

1. ______________ is the process of a species losing an electron (as a product in a ½ reaction).

2. A(n) _______________ cell is one for which the process we are interested in is the production of electricity from a spontaneous chemical process.

3. A(n) ______________ is the interface between the electrical and the chemical part of an electrochemical cell.

4. The _______________ potential (or EMF) for a cell is the value determined when all gases involved in the electrochemical process are present at a pressure of 1 atm, and all dissolved species are present at a concentration of 1 molar.

5. The ____________________ is the ½ reaction with a defined potential of 0V, to which all other ½ cell potentials are compared.

6. The __________ equation will allow us to calculate the potential for a cell under any given set of conditions.

7. _________________ is the process of using electricity to force a non-spontaneous chemical process to occur - usually used for the deposition of reduced metals on cathodes.

8. A(n) _______________ anode is made up of an 'expendable' species in contact with a metal for which you need to retain the integrity - such as magnesium is used to retain the integrity of an iron oceangoing vessel.

9. Radioactive _____________ is the spontaneous decomposition of an unstable nucleus.

10. __________________ is the only nuclear process which incorporates an inner shell electron into the nucleus.

11. The ____________________________ comes from a plot of the ratio of neutrons to protons in the nucleus of stable isotopes.

12. A radioactive _______________ is the path an unstable isotope will follow to become stable.

13. _______________ is the process of changing one element into another.

14. A(n) ______________ reaction occurs in fissionable material when the number of neutrons released by the fission is equal to the number of neutrons absorbed.

15. One of the units for the measure of radioactivity is the ___________________.PROBLEMS (Point totals are shown in parenthesis) Show your work and circle you answers where appropriate for full credit.

16. (15) Balance the following redox equations in an acidic (A) or basic (B) solution as indicated: [NOTE: You may have to add H₂O, H⁺, or OH^- as necessary.]

a) Fe²⁺ + Cr₂O₇^2- Fe³⁺ + Cr³⁺ (A)

b) MnO₄^- + C₂O₄^2- Mn²⁺ + CO₂ (A)

c) MnO₄^- + Br^- MnO₂ + BrO₃^- (B)

17. (15) Consider the following reaction: Cu²⁺ + Zn Cu + Zn²⁺

a) Write the 2 ½ reactions that make up this overall reaction, identifying both the cathode and the anode.

b) Calculate the potential for this cell if [Cu²⁺] = 5.0M and [Zn²⁺] = 0.0050M.

[For Cu²⁺ + 2e^- Cu, E = 0.337V; for Zn²⁺ + 2e^- Zn, E = -0.763V]

18. (10) Calculate the mass of zinc that can be recovered from a solution containing Zn²⁺ when a current of 2.75A is passed through the solution for 8.00 hours.

19. (15) Determine the age of a sample of wood if 1.00g of the wood exhibited a decay rate of 4.27 scintillations/minute, when 1.00g of a 'fresh' sample of the wood has a decay rate of 18.6 scintillations/minute. The ½ life of ¹⁴C is 5,730 years.

20. (15) Calculate the nuclear binding energy/mole (in Joules) and the binding energy/nucleon (in Joules) for ⁵⁷Co, given an atomic mass of 58.9332 for this isotope. [Neutron mass = 1.00728; Proton mass = 1.00867; Electron mass = 0.00055]

EXTRA CREDIT (10) ²³⁷Np decays to form ²⁰⁹Bi. Determine the number and type of decay processes this transmutation series must have.