Demonstration 3

Test Tube Geology

Corrosion of Iron

Objective: The objective of this experiment is to observe over a period of several days the corrosion of iron nails in a test tube.

Time Required: The initial set up will require fifteen to twenty minutes which includes time to mass the copper(II) sulfate. Five to ten minutes each day can then be spent recording observations until no more changes are observed.

Materials and Supplies:

2.5 to 5.0 g CuSO₄. 5H₂O

NaCl (twice as much volume as that of copper (II) sulfate)

two circles of filter paper or paper toweling

2 to 3 small nails

test tube

test tube rack

long stirring rod

General Safety Guidelines:

• Wear goggles when using copper (II) sulfate.

• Wash hands well.

• Discard test tube contents in trash or other receptacle when finished.

Procedure:

1. Use the test tube as a template and cut out two small filter paper disks.

2. Mass 2.5 to 5.0 g of copper (II) sulfate pentahydrate and place into a standard size test tube. See diagram of setup.

3. Place one of the paper disks in the test tube and use the stirring rod to push it flat against the copper(II) sulfate.

4. Add Sodium chloride to twice the depth of that of the copper (II) sulfate.

5. Place the second paper disk on top of the sodium chloride layer.

6. Place two or three nails on top of the paper disk and slowly add enough water to cover the entire contents.

7. Sketch and label the contents of the test tube each day. Record any observations.

Questions:

1. Which is the more active metal, sodium or iron?

2. Which is the more active metal, copper or iron?

3. Write the reaction which allows the iron to corrode.

Answers to Questions:

1. Sodium is the more active metal. The iron does not react with the sodium.

2. Iron is more active than copper. The iron is oxidized and the copper is reduced.

3. 2Fe + 3Cu⁺⁺ --> 2Fe⁺⁺⁺ + 3Cu