Redox Lab Part 1(Electrochemical cells and half reactions)

Redox reactions

•Concerned with the transfer of electrons between atoms

•For every reduction there is an oxidation

•For every oxidation there is a reduction

•2 half reactions (reduction and oxidation)  1 whole reaction

Al(s) + O2(g)  Al2O3(s)

•Reduction = gain electrons (anything that does this is an oxidizing agent)

•Half reaction

• ______

•Oxygen is reduced

•Oxygen is the oxidizing agent

•Oxidation = lose electrons (called the reducing agent)

•Half reaction

•______

•Al is oxidized

•Al is the reducing agent

Electrical potential

•Electrons move when they are transferred from one element to another

•This movement has potential energy - can be measured in volts

•Redox reactions provide the energy in batteries

• Living organisms can also obtain their energy form redox reactions.

Electrochemical Cells

•chemical energy converted to electric energy

•Redox = electrons are transferred from on thing to another

•To make an electrochemical cell, separate the half reactions

  • Reduction happens in 1 beaker
  • Oxidation happens in the other
  • Connect the 2 half reactions with a wire  flow of electrons
  • Add a salt bridge (electrolyte) to prevent a build up of electrons on one side to keep the reaction going.

Materials:

2- 250ml beakers, one U-tube, cotton, voltmeter, wire connectors and alligator clips, strips of zinc and copper, copper II nitrate solution, zinc nitrate solution, calcium sulfate solution

Procedures:

1)set up an electrochemical cell with 2 beakers – fill one with about 150 ml zinc sulfate and the other with about 150ml copper II sulfate

2)Place the copper strip into the copper(II) sulfate solution and the zinc strip into the zinc sulfate solution

3)Attach the alligator clips from the voltmeter to the metal strips

4)Prepare the salt bridge by filling the U-tube with calcium sulfate and plugging the ends with cotton plugs.

5)Place the U-tube so that one end is in each of the 2 beakers of the reaction

6)Watch the multi-meter. If the reading is negative, switch connections to the voltmeter. Note the magnitude and direction of the voltage and record observations in the results section. (remember that red = + an black = -)

Results:

Electrodes / Voltage / Direction of electron flow
Copper – zinc

Analysis questions:

1)Write the two half reactions taking place in your electrochemical cell.

  1. Oxidation reaction
  1. Reduction reaction

2)What is the oxidizing agent in this cell?

3)Anaerobic sulfur reducing bacteria get their energy by reducing sulfur accordingly: H2 + SO4  H2S + H2O

Balance this reaction in the space below (Hint: start by making sure there is an = # of oxygen molecules on each side of the equation)

4)Write the half reaction for the reduction of sulfur in this reaction.

5)Given the formula below write the half reaction for the reduction of iron(III) that occurs at gypsum. Include oxidation numbers for Fe on both sides of the reaction.

H2S + Fe+3  FeS + H2