OPTION 2
WORKSHEET
6
CORROSION
Syllabus references 9.6.2 & 9.6.4
1
a
Define corrosion.
b
A group of students was investigating the conditions under which rusting occurs. They obtained
four iron nails and placed each nail in separate test tubes. Into test tube 1 they added tap-water,
test tube 2 salt water, test tube 3 boiled water (to remove dissolved oxygen) covered by a layer
of oil to prevent air dissolving, and test tube 4 drying pellets, and stoppered it.
stopper
oil
tap
water
salt
water
boiled
water
drying
pellets
1
2
3
4
The following results, showing the amount of rust (the more crosses the more rust), were
obtained.
Amount of rust
TEST TUBE 1
TEST TUBE 2
TEST TUBE 3
TEST TUBE 4
xx
xxx
x
nil
Use this information to describe the conditions necessary for rusting to occur.
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
OPTION 2 WS 6
2
A group of students was investigating rusting. They took two clean iron nails and bent one, then
placed them in a Petri dish and covered them with an agar solution to which had been added
potassium hexacyanoferrate(III) and phenolphthalein. After a couple of days they noticed areas of
pink and dark blue forming around the nails and sketched the following results.
Petri dish
Dark blue
Pink colour
The students knew that phenolphthalein is colourless below pH 8.3 and pink above pH 10. They
also knew that iron(II) ions react with hexacyanoferrate(III) ions to produce a dark blue colour
according to the reaction:
K(aq)  Fe2(aq)  Fe(CN)63(aq) → KFe[Fe(CN)6](s)
3
a
On the diagram above identify the sites of oxidation and reduction.
b
Write the oxidation and reduction half-reactions for the above.
c
What effect on corrosion did bending the nail have compared to the unbent nail?
d
The students allowed the agar to dry out and noticed that a reddish brown substance formed.
Name this substance and write its chemical formula.
Aluminium is a more active metal than iron but appears to corrode far less readily than iron.
Explain why.
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
OPTION 2 WS 6
4
5
a
Define the term ‘passivating metal’.
b
While iron is not a passivating metal, stainless steel is. What has been added to iron to make
stainless steel rust resistant?
Classify each of the following statements as true or false. For those statements that are false,
rewrite them so they are true.
a
Rusting and corrosion of iron are different processes.
b
Oxygen and water are necessary for rusting to occur.
c
Iron will rust less quickly in salt water than fresh water.
d
Attaching copper to iron will protect the iron from corrosion.
e
Pure iron rusts less rapidly than impure iron.
f
Copper is a passivating metal.
Copyright © 2007 McGraw-Hill Australia
CONQUERINGCHEMISTRY HSC
OPTION 2 WS 6