Thursday, 19 February 2015

9.3.2 - Laboratory Activity : Comparing the rate of corrosion of iron, steel and stainless steel

Laboratory Activity 9.3.2:
Comparing the rate of corrosion of iron, steel and stainless steel
Aim: To define the rates of rusting between iron, steel and stainless steel.
Problem statement: How does the rusting of iron compare to steel and stainless steel?
Hypothesis: Iron is easily corroded, followed by steel and stainless steel.
Variable:
» Fixed variable : Experimental conditions
» Manipulated variable : Types of nails
» Responding variable : Rate of corrosion

Material:
» Iron nails
» Steel nails
» Stainless steel nails
» Potassium hexacyanoferrate(III)
» Jelly

Apparatus:
» Beakers
» Test tubes
» Test tube rack
» Sand paper
Procedure:

The animation below shows the arrangement of apparatus and the observation of the experiment.

(A) With chlorine
1. Each nail is cleaned with sand paper.
2. Iron nail is put into test tube A, steel nail is put into test tube B and stainless steel nail is put into test tube C.
3. 5g of jelly is dissolved in 100cm3 of boiling water. 1cm3 of potassium hexacyanoferrate(III) are added into the jelly.
4. The test tube A, B and C are filled with jelly until all nails are completely submerged.
5. The experiment set-up is put aside for three days, and the results are studied.
Results:
Test tube Nails Observation Inferences
A Iron nail The jelly around the nail turn bluish The iron nail has rusted
B Steel nail Small amount of jelly around the nail turn bluish Iron nail has a slight rust
C Stainless nail No changes No rusting occurred
Discussion:

Iron will form iron(II) hydroxide.
2Fe(s) + O2(g) + 2H2O(l) → 2Fe(OH)2(s)

The potassium hexacyanoferrate is to detect the presence of the rust that has formed.

The bluish colour detected in the test tube indicate that the iron has rusted.
Conclusion:

Iron corrodes easily, steel corrodes slightly, while stainless steel does not corrode at all in the presence of water and air.

The hypothesis is accepted.


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