Name: __________________________________                           Class: _____________

Corrosion in Metals Lab

Introduction

            In this lab you will be investigating the corrosion process in steel and how that is affected by protective layers. The layer of protection is accomplished by cathodic protection in which the more reactive metal will be preferentially corroded leaving the less reactive metal uncorroded. You will be experimenting with unprotected iron, iron protected by copper, and iron protected by zinc.

Materials

-2 petri dishes with covers                                          -glass stir rod

-1.5 g powdered agar (not nutrient agar)                    -distilled water

- 0.1M postassium ferricyanide in dropper bottle        -250mL beaker

-100mL 0.1M sodium nitrate                                     -burner/hot plate

-white background paper                                           -glass stir rod

-black background paper                                           -100mL phenolphthalein indicator

-beaker tongs                                                            -10cm  length copper wire

-steel wool                                                                -10cm length of zinc wire or strip      

-three 6cm x 1cm iron strips

Procedure

1. Heat 100mL of 0.1 M sodium nitrate to boil in a 250mL beaker. While stirring with a glass rod, add 1.5g of powdered agar. Heat and stir the mixture until agar forms a suspension.

2. Add 10 drops of 0.1M potassium ferricyanide and 10 drops of phenolphthalein indicator to the agar suspension. Stir to mix thoroughly.

3. Clean three 6cm x 1cm iron strips with steel wool.

4. Place one of the iron strips in the bottom of the first Petri dish.

5. Polish the 10cm copper wire and the 10cm zinc wire with steel wool.

6. Lightly wrap the 10cm copper wire around the second 6cm x 1cm iron strip.

7. Lightly wrap the 10cm zinc wire around the third 6cm x 1 cm iron strip.

8. Place the second and third wrapped iron strips in the bottom of the second Petri dish. Do not allow the two wrapped strips to touch each other.

9. Pour enough warm agar in both Petri dishes to cover all of the iron strips to a depth of about 1mm.

10. Make observations against both white and black backgrounds on the data table for Day 1.

11. Cover both dishes and let stand for about 24 hours.

12. On day 2, observe the Petri dishes again and record under Day 2 on the data table.

                                                              Data

Questions

1. Why does the iron behave differently in the three cases observed in this experiment?

2. Explain how cathodic protection works.

3. What conclusions can be drawn from the colors of the indicators?

4. On day 2 what did you notice about the zinc wire wrapped around the steel in Dish 2? What might this be?

5. Can you think of any other uses for the processes you observed in this experiment?

6. Have you heard about the bridge that collapsed in Minneapolis, Minnesota? Do you think corrosion may have played a role in this collapse?