PROBLEM: What effect does bacteria have on the rusting rate of iron?
HYPOTHESIS: If the amount of bacteria present increases, the rusting rate of iron will increase.
BACKGROUND INFORMATION:
Rust is a reddish-brown, flaky oxide formed on iron when it is exposed to moist air and becomes corroded. The chemical reaction of iron reacting with moist air to form rust is 'Fe2O3 -> X H20', where X = the amount of water present. This variable also determines the shade of color of the rust. The rust, or iron oxide, is a solid and has the same general form of its metal origin, however the oxide is much more weak and brittle. This brittle oxide does not adhere well to the surface of the metal and often flakes off, otherwise known as "pitting". Large amounts of pitting lead to structural weakness and eventually metal disintegration. Iron rusting is a common problem affecting cars, bicycles, and a wide range of other important items used in everyday life, therefore if bacteria affects the rusting rate of iron, anti-bacterial solutions could be used to help prevent or slow the rusting of these items. Every year, millions of dollars in damages are lost due to corrosion. Thus far, there are three common methods to preventing the rusting of iron:
1) Coat the iron with a material more reactive to the corroding substances so that it will protect the iron while being consumed.
2) Alloy the iron to be chemically resistant to corrosion.
3) Cover the iron with an impermeable surface coating to lock out all
air and moisture, which cause the rusting.
Therefore, if certain bacteria produce oxygen, it would stand to reason that increased amounts of bacteria may have a direct relationship to the amount or speed of rusting.
Bacteria are the most common organism on Earth, and are connected in some way to all living organisms. They are microorganisms containing no nucleus with a cell wall composed of peptidoglycan, a protein-sugar molecule. The main particular bacteria possibly involved with iron rusting would be cyanobacteria, a photoautotroph that obtain their energy through photosynthesis. Cyanobacteria produce atmospheric oxygen, thereby possibly enhancing the oxidation process that creates rust. Cyanobacteria is present in almost every atmosphere/habitat worldwide; it can be found from oceans, to bare rocks, to soil, to fresh water lakes. Along with this result from cyanobacteria, other bacteria could affect the rusting rate of iron due to the fact they secrete acids as they grow. Because acid increases the rate of corrosion, this secretion could allow for microbes present on the iron to cause the metal to rust much more easily.
Therefore, bacteria could have a significant impact on the rusting rate of iron. This discovery would prove to be significant due to the fact that millions of dollars are being spent due to corrosion-related damages every year, and the presence of bacteria in this damage is often overlooked. If bacteria is indeed a factor, it would be easily feasible to produce methods to prevent, counter or slow bacteria in danger areas, thereby preventing, countering, or slowing the rust itself.
MATERIALS:
Three iron nails
sample of bacteria
Three glass jars of distilled water
sandpaper
Any strong anti-bacterial agent
(ex. Ultra Palmolive Antibacterial
hand soap)
PROCEDURE:
1) Gather all materials.
2) Clean the nails of any oily substance or other surface abnormality by sandpapering the iron nails thoroughly.
3) Label one glass jar 'experimental', one 'experimental2', and the other 'control'.
4) Locate an appropriate environment for the glass jars, with a constant location, temperature and humidity.
5) Fill the jars about halfway with distilled water, then drop one iron nail into each jar.
6) In the glass jar labeled 'experimental', drop the sample of bacteria in it. (This could be obtained from a simple dirt sample from the environment.)
7) In the glass jar labeled 'experimental2', place the anti-bacterial agent (Palmolive) in it to completely protect it from any bacteria growth. Leave the glass jar labeled 'control' untouched, containing only the distilled water.
8) Observe the rusting of the nails over a period of elapsed time (ex. 72 hours), recording the amount of rusting after each time interval (ex. 12 hours) for each jar.
9) Conduct the experiment again with the exact same steps (or conduct it on a separate set of 3 glass jars at the same time) and record your findings to help obtain accurate results.
10) Compare and/or average the two sets of data results, and interpret or
visualize the results. Draw a conclusion on the affect of bacteria upon
the rusting rate of iron.
RESULTS:
Bio-Rusting Experiment - Tables
The affect of bacteria upon the rusting rate of iron in a 72 hour trial period. IV: Bacteria. DV: Amount of rust. Constants: Time, distilled water, temperature, location (indoors).
1st Trial
Time Interval Experimental(with bacteria) | Experimental 2(with anti-bacterial) | Control(Distilled Water)
12 (hours) Dark orange widespread rust on the tip, end, and all along the nail. | No evidence of any rust. | Significant rusting on the tip and minor rusting on the end. No evidence of rust along the length of the nail.
24 Widespread rust remains, no evidence of spreading. | Nail appears to be getting coated with a different color rust then the others, a blackish coat as opposed to the red-yellow-brown of the others. Black rust minorly evident throughout the nail. Rust spreading throughout the nail, beginning to completely engulf it. Several spots of the nail remain rust-free, however.
36 Little or no evident change. | Blackish rust spreading, hard to distinguish among the nail's actual color, but easily flakes off. | Nail appears to be almost completely coated with a layer of reddish-orange rust, with a few minorly discernable spots of the original nail color.
48 Little or no evident change. | Blackish rust has almost completely coated the nail, although still very hard to distinguish. | Rust partially flaking off, although still significantly covering the nail to the point where there is very, very minute spots remaining of the nail's original color.
60 Rust is beginning to take on a darker shade, but does not appear to be spreading. | Nail is completely coated by the blackish rust. No flaking evident unless nail is moved. | Little or no evident change.
72 The rust is a very dark shade, similar to that found on the control. | Little or no evident change. | Little or no evident change.
2nd Trial
Time Interval Experimental(With Bacteria) Experimental 2(With anti-bacterial) Control(Distilled Water)
12 (hours) Significant orangish brownish rust development on the head, end and all along the nail. Minor black rusting on the head of the nail only. Significant orangish-yellowish rusting evident all along the length of the nail, however, only on its underside.
24 Rust spreading, but no significant change. Black rust beginning to appear on the end of the nail, and, in a couple spots, on the shaft of the nail. The underside of the nail is completely covered with bright orange rust. It is beginning to spread to the sides and top part of the nail as well.
36 Little or no evident change. Black rust spreading along the nail methodically. Very little change. Most of the rust is still confined to the underside of the nail.
48 Little or no evident change. The black rust, still very indistinguishable as in the first trial has spread to overtake most of the nail. Very small, spotty unrusted places along the nail. The rust has spread to the outer parts of the nail. Some signs of corrosion in the nail appear to be evident as well.
60 Little or no evident change. The nail appears to be completely coated in the black rust. The nail looks to be completely rusted over, with spotty corrosion occurring in various spots along the nail's length. Major flaking off of the rust occurring.
72 Little or no evident change. Little or no evidentchange. Little or no evident change.
INTERPRETATION:
The results obtained from my experiment reveal a number of interesting facts regarding the affects of bacteria upon the rusting rate of iron. They directly showed that there was no obviously evident affect by the bacteria upon the rate of rusting, but instead that it had some affect on other areas associated with the rust. For instance, in both trials, after a 24 hour period all three nails had showed signs of rusting. In the first trial, the nail exposed to the bacteria showed more immediate rusting, but this finding was contradicted by the second trial, which showed the control nail, exposed only to the distilled water, to have the more immediate rusting. In both trials, the control nail experienced the greatest amount of rust on the nail by the end of the experiment. It is also worth noting, however, that the nail exposed to the bacteria, in both cases, seemed to stop rusting after about a 36 hour period, while the other nails continued to rust at a rapid pace. This is an unexpected side-affect that possibly could have resulted from the bacteria in the jar secreting chemicals that covered the nail, stopping the rusting process. Another feasible result would be the bacteria (obtained from a simple dirt sample) could be slowing the circulation of oxygen into the jar, consuming the oxygen in the jar, or the dirt itself coating/covering the nail, preventing it from rusting. Other possibilities include the bacteria from the dirt sample were unable to reproduce in the glass jars, thereby not sustaining the appropriate environment, leading to inaccurate results, or that the bacteria could have simply been the wrong type, and therefore not have the expected affect upon the rusting rate of iron. Also, other elements contained inside the dirt sample could have had unexpected results and affects upon the experiment. One of the main discoveries from my experiment was the impact of bacteria on the color of the rust formed. In both trials, the nail exposed to only the distilled water formed the brightest shade of rust, an orange-yellowish color, the one with bacteria formed a dark yellowish brown rust, while the one with the anti-bacterial solution formed the dark black rust. These findings seem contradictory, as there is no logical pattern; the expected results would have been for the one with the anti-bacterial to be the lightest, the control in the middle, and the one with bacteria the darkest, or vice versa. However, because the nail exposed to anti-bacterial solution formed the darkest rust, and the nail exposed to bacteria formed the second darkest rust, there is no obvious direct relationship between the presence of bacteria and the color of the rust, but it is apparent that there is some sort of indirect relationship. According to the equation in the relevant information for the chemical reaction of iron reacting with moist air to form rust, 'Fe2O3 -> X H20', X, the amount of water present, should determine the shade of the rust. However, my findings contradict that; in my experiment the amount of water present was a constant, controlled to be at the same level, in identical jars for all three nails. This question, then, becomes an excellent topic for a second future experiment.
CONCLUSIONS:
My experiment concluded that bacteria has no direct, obvious or apparent affect upon the rusting rate of iron, proving my hypothesis wrong. It showed some evidence that bacteria may have an indirect affect on rust, by halting it from continuous spreading. It did, however, produce an unexpected result proving that bacteria does have some sort of indirect affect upon the color of the rust on the iron.
IMPLICATIONS/FURTHER STUDY:
It would be very plausible to conceive an experiment that would be more fine-tuned to the secondary results of this experiment, the affect of bacteria on the color and shade of rust, and to analyze exactly how and why this is happening, and upon arriving at those findings, to see if it is possible to control the shade of the rust with the use of a variable, which is not apparent in the results of my experiment. It would also be plausible to redo this experiment with better controlled constants; using limited resources, I could only partially maintain a stable temperature and humidity, which, although all three jars were exposed to the same conditions at all times, could have some unforeseen side-affects. Another feasible route of further investigation would be to conduct an experiment designed to specifically test the side-affect noted in the interpretations, in which the bacteria seemed to absolutely halt the continued rusting of the iron. If these are directly related, the ability to manipulate such results in to real life rust-prevention methods would be invaluable. Finally, the experiment could be re-done with a variety of different, specific bacteria, rather then a simple dirt sample, to insure more accurate conclusions.
WORKS CITED
· Microsoft Encarta Encyclopedia 1999.
· http://www.pumpmate.com.au/barts/qc-irb.htm "Iron Related Bacteria"
· http://www.ng.hik.se/~njasv/disp.html "Cyanobacteria"
· http://www.madsci.org/posts/archives/mar97/853477172.Cb.r.html "Does Rusting of Iron Commonly Involve Bacteria?"
· http://www.eskimo.com/~billb/scifair/bio.html#med "Science Fair Idea Exchange: Bio-Rusting"
· http://naio.kcc.hawaii.edu/chemistry/everyday_corrosion.html "Corrosion"