CIP2
CORROSION
Last Revised: February 2014
1. PURPOSE
This exercise examines some of the factors associated with corrosion.
2. REAGENTS & EQUIPMENT
2.1 Iron nails
2.2 Pliers & files
2.3 Copper foil
2.4 Aluminium foil
2.5 Magnesium or zinc foil
2.6 Sheet mild steel, tinplate and galvanised steel
2.7 Olive oil or paraffin oil
2.8 Agar solution with phenolphthalein and ferricyanide added
2.9 Petri dishes & test tubes
2.10 Ferricyanide solution
2.11 Hexane
2.12 0.1 M sodium chloride, sodium hydroxide, hydrochloric acid, sodium phosphate
2.13 AA battery
3. PROCEDURE
All nails used in this exercise must be rinsed in hexane and dried with paper towel before use to
remove any grease residues which will affects the results.
3A. Factors affecting corrosion
3.1 Place an iron nail in each of twelve test tubes, marked A-L.
3.2 Set up the test tubes as follows. Unless otherwise indicated, the nail should be covered and
the same volume of liquid used in each case.
A. Partly cover the nail with a solid moisture absorbent (eg dried MgSO4)
B. Distilled water.
C. Partly cover the nail with distilled water.
D. Freshly boiled distilled water, and then pour a thin layer of olive oil on top.
E. 0.1 M sodium chloride
F. 0.1 M sodium hydroxide
G. 0.1 M hydrochloric acid
H. 0.1 M sodium phosphate
I. Tap water
J. Tap water, with a thin layer of olive oil on top
K. wrap copper wire around the nail, and cover with tap water
L. wrap magnesium foil around the nail, and cover with tap water.
CIP2 Corrosion
3.3
3.4
3.5
Leave for 1 week.
At the end of this period, examine each for evidence of corrosion and record your results.
Add 1 drop of potassium ferricyanide solution (which turns from yellow to blue in the presence
of Fe2+) to each test tube except A. Note the intensity of colour formed.
3B. Mechanism of corrosion
3.6 Arrange four nails in separate petri dishes as follows:
3.7
3.8
3.9

Dish 1 – one straight nail

Dish 2 – one bent nail

Dish 3 – nail partly wrapped in copper foil
 Dish 4 – nail partly wrapped in zinc foil
Pour lukewarm agar (containing phenolphthalein & ferricyanide) over the nails, ensuring that
they are well covered.
Place sheets of aluminium foil into two petri dishes. Cover one with distilled water, the other
with 0.1 M NaCl.
Observe the results in each petri dish after one week.
3C. Demonstrations
3.10 Samples of mild steel, tinplated steel and galvanised steel will have their surface scratched and
a small amount of the indicator agar solution poured over the scratch.
3.11 Colour formation will occur within 15 minutes. Record your observations.
3.12 A nail will be attached to each terminal of a AA battery, and the tips of the nails immersed in
water. Record your observations after a short period of time and after one week.
4. REPORT
Discussion

discuss each set of results in Part 3A in terms of the differences in the degree of corrosion
caused

construct a table which summarises those factors which (a) increase and (b) decrease
corrosion

discuss the effect of different metals in contact with iron

discuss the effect of stress (i.e. bending, shaping) on the iron

in Parts 3B & 3C, explain why the phenolphthalein and ferricyanide change colour in certain
areas of the nails (write equations to help explain)

explain the difference in behaviour of the two pieces of aluminium foil

explain the difference in behaviour of the two nails attached to the battery
Questions
1.
How does galvanising protect steel from rusting?
2.
Magnesium or zinc blocks are often connected to objects made from steel (e.g. ships, large
drums and tanks) to prevent rusting. Explain why this would work.
3.
Tin cans are made from steel coated with tin. They resist corrosion better than uncoated steel,
but once they are scratched, corrosion is greatly accelerated. Explain why.
4.
Aluminium is an extremely reactive metal, yet is used instead of iron in situations where rapid
corrosion is likely. Explain why aluminium does not corrode as rapidly as iron.
p2