Topics: Chemistry, Iron, Corrosion Pages: 13 (2400 words) Published: February 25, 2015
Mayceemae M. Barnuevo
CHEM 17.1 13L
Group 1

February 7, 2014
February 19, 2014

Exercise 12

Metals undergo natural destruction that allows a spontaneous deteriorating reaction where they return to their original state from where they are obtained upon contact with the surrounding, particularly when reacted to oxygen. Such phenomenon is known as corrosion (Zumdahl, 1998). This leads the surface of the materials to rust in due time. Usually, this kind of process is electrochemical but is sometimes accompanied by mechanical and physical stress that causes the metal to corrode (Heitz et al, 1992).

Iron, a common type of metal in the form of alloy steel which is widely used in construction firms, gradually corrodes upon being oxidized into ions of irons by oxygen and forms rust as a result of electrochemical reaction. In addition, at room temperature, pH, presence of water and electrolytes would also contribute to the formation of rust on its surface (Wilbraham et al, 2003). The objective of this exercise is to state the effects of the following factors on the corrosion of iron:

1. acidity and basicity of the solution in contact with the metal; 2. mechanical stress applied on the metal; and
3. contact with other metals.



A. Reagents
0.1 M potassium ferricyanide, K3Fe(CN)6
ferrous sulphate, FeSO4
sodium hydroxide, NaOH
sodium chloride, NaCl
hydrochloric acid, HCl
potassium hydroxide, KOH
potassium nitrate, KNO3
nitric acid, HNO3
trisodium phosphate, Na3PO4
sodium thiocyanate, NaSCN
sulfuric acid, H2SO4
distilled water, dH2O
B. Apparatus
test tubes

iron ring

250-mL beaker

iron stand

bunsen burner
C. Others
iron nails

copper strip

sand paper

zinc strip




A. Reactions of Iron with various Aqueous Solutions
In determining the reactions of iron immersed in various aqueous

solutions, three set-ups were made, each consists of four test tubes with iron nails immersed in different sets of solutions – Set-up A with NaOH, NaCl, HCl, and dH2O; Set-up B with KOH, KNO3, HNO3, and dH2O; and Set-up C with Na3PO4, NaSCN, H2SO4, and dH2O. The iron nails were allowed to stand overnight in the solutions, and changes that have occurred were recorded. After letting it stand, two drops of 0.1 M K3Fe(CN)6 solution were added into each test tube. Changes were observed and recorded.

In a separate test tube, a drop of 0.1 M K3Fe(CN)6 was added into a test tube with 1 mL FeSO4 solution. Visible observations in the reaction were noted. B. Reactions of Iron as affected by Mechanical Stress

In determining the reactions of iron as affected by mechanical stress, a wet tissue paper dropped with K3Fe(CN)6 and phenolphthalein, instead of an agar medium, was placed inside a beaker. A clean straight nail was placed on one side of the beaker and a bent nail on the other side. This beaker was allowed to stand overnight. Changes that occurred were recorded. C. Reactions Involving Metal Couples – Two Metals in Contact In determining the reactions between two metals in contact, two metal strips and iron nails were used. A clean piece of copper strip and zinc strip were wound separately around a clean iron nail. The nail was removed in each strip.


Before the nail was reinserted, the coil was tightened to make a tight contact between the two metals. These two nails were placed discretely in a beaker with a wet tissue paper and were allowed to stand for a night. Effects of metal coupling were recorded.


Data/ Observations
Table 12.1. Reactions of Iron with various Aqueous Solutions after addition of O.1 M K3Fe(CN)6

Acidic, Basic, Neutral



Yellow green mixture


Rust was slightly visible,

Set-up A

green, cloudy mixture


Blue mixture, rust was
slightly visible

Set-up B


Bibliography: Heitz, E., Henkhaus, R., Rahmel, A. 1992. Corrosion. In Academic American
Petrucci, R. H., Herring, F. G., Madura, J. D., and Bissonnette, C. 2011.
Silberberg, M. S. 2013. Principles of General Chemistry. 3rd ed. New York, NY.
Wilbraham, A. C., Staley, D. D, Matta, M. S. and Waterman, E. L. 2003.
Whitten, K. W., Davis, R. E., Peck, M. L., Stanley, G. G. 2010. Chemistry. 9th
Zumdahl, S. S. 1998. Chemical Principle. 3rd ed. Boston. Houghton
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