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.