Honors Chemistry - Electrochemistry Test

  1. Assign oxidation numbers to each element in the following compounds and ions.
  2. (NH4)2HPO4 NCl3 NI3 nitrous acid I3-1

  3. Balance the following reactions using any method you choose.
  1. Bi2O3 +OCl- ---> BiO3- + Cl- (basic)
  2. copper metal reacts with perchloric acid to form chloride ions and copper (II) ions
  3. Magnesium metal reacts with bromine gas to form magnesium bromide

d) MnO4- + Fe+2 ---> Fe+3 + Mn+2

3. Below you will find two balanced half reactions. Draw the galvanic cell that could be produced from these reactions Calculate the voltage on the cell. Be sure to include the following things in your drawing:

What is in each beaker What is in the salt bridge

What the electrodes are made of What direction the electrons flow in the wire

What direction the ions flow in the salt bridge Where reduction occurs/where oxidation occurs

The anode and cathode

Mg+2 + 2 e-1à Mg 4 H2O + CrO4-2 + 3 e-1 à Cr(OH)3 + 5 OH-1

 4. What principle of kinetics (the unit on rates of reactions) is the set-up in #3 (a galvanic cell) violating? Why is that possible?

  1. Draw the set-up used to gold plate an aluminum tennis racquet. Write out the reactions that occur at each electrode. Is the racquet the anode or cathode?
  2. Draw the set-up to electrolyze molten (melted) sodium bromide. Write out the reactions that occur. Calculate the voltage needed to perform this electrolysis. How would this be different if the sodium bromide were aqueous?
  3. What makes a rechargeable battery or cell rechargeable? In other words, what makes it different from a non-rechargeable battery or cell?
  4. One of the dangers of car batteries we discussed in class was that occasionally these batteries explode while a car is being jump-started. How/why does this happen?
  5. In order to protect cars from rusting, they can be coated in paint and/or wax. Why does this help?
  6. Some car manufacturers use galvanized steel to further protect their cars from rusting. What is galvanized steel and how does it protect against corrosion?