Introduction

Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.[1] While rust in itself can be viewed as an inconvenience more than anything else, it can cause significant problems. It is known to encourage the growth of a specific type of bacteria that causes tetanus; a serious, communicable and potentially life threatening disease.[2]

Following the Boxing Day tsunami of 2004, an epidemic of tetanus occurred in Aceh, Indonesia. Because of the loss of property, lack of vaccinations, and exposure to everyday rust among the majority, an outbreak of tetanus occurred. It was concluded after the outbreak was controlled that in the context of natural disasters, preventive measures against tetanus, including wound cleaning and active and passive immunization, should be routinely conducted.[3]

 Taking these events and findings into account, preventative measures could likely include stopping the formation of rust on metals before tetanus has a chance to form could be an effective solution. In this lab the question was asked, “how is the rate of corrosion of iron affected by the presence of ocean water in comparison to the rate of corrosion in distilled water?” In response it was hypothesized that iron will oxidize faster in salt water than in distilled water because acidic conditions encourage oxidation.

Pre-Lab Questions

  • What is a chemical equation for rust formation?

The chemical equation for rust formation is 4Fe + 3O2 -> 2Fe2O3[4]

  • When a metal corrodes, is it oxidized or reduced?

 When a metal corrodes it is oxidized.

  • Describe what the terms independent, dependent, and control variables mean.
    1. The dependent variable is what is being tested in an experiment and is “dependent” on the independent variable.[5]
    2. The independent variable determines the reaction of the dependent variable.[6]
    3. A control variable is a constant, unchanging standard used for comparison in an experiment.[7]

Materials

  • Protective gloves (open cuts on the hands increase the chance of tetanus)
  • Beakers (47.458g per beaker) 
  • Iron nails
  • Distilled water
  • Sodium chloride (neutral)
  • Magnesium oxide (basic)
  • Zinc sulphide
  • Calcium carbonate (a salt, strong base)
  • Potassium chloride (neutral, composed of a strong acid and base)
  • Scoopula
  • Scale
  • Weigh boat
  • Tape
  • Marker
READ
Haber Process

Observations

Water Salt Water
Water is yellowish/greenish
Yellow precipitate floats, sits on the bottom of the beaker
No smell
Nail is rusted on the bottom and top, less on the middle of nail
Rust comes off easily
Rust gathers in dents on the nail
Tip of nail is very corroded
Precipitate keeps it shape when stirred
No film on glass  
Water is orange
A lot of precipitate formed
Cloudy film formed in liquid and on beaker
Rust is red and forms around the water line of the nail
Rust has an acidic odour
Solution smells metallic
Bottom of the beaker is white
Solution becomes opaque when stirred
Film comes off like ice on glass  

Procedure

  1. Weigh the beakers and record their individual weights
  2. Weigh each nail and record their weight
  3. Measure 100mL of water into each beaker
  4. Label one beaker “water” and the other “ocean water”
  5. Measure the required amount of salt, magnesium oxide, etc.
  6. Add the magnesium oxide, salt, zinc sulphide, calcium carbonate, potassium chloride to the beaker labelled “ocean water”.
  7. Stir the “ocean water” until it turns opaque and white in colour
  8. Put a nail inside each beaker
  9. Let sit for two days
  10. Observe results

Discussion

  • What was the control in your experiment? Why was it the control?

In this experiment the nail in the distilled water was the control because it showed the average amount of oxidation that would occur with nothing added to the water. It was compared with the reaction with ocean water to contrast how quickly the nail oxidized in ocean water.

  • Did the factor that you chose to investigate have an effect on the rate of corrosion?

It had an extreme effect on the rate of corrosion when compared to the control.

  • Write the chemical equation for this reaction. Which element is being oxidized?

Water: 4Fe + 3O2 -> 2Fe2O3.  -> Here iron is being oxidized

Salt water: NaCl+MgO+H2O+ZnS+KCl+CaCO3+Fe

  • Explain why more rust formed on the “ocean water” nail than on the distilled water nail.

Salt water contains lots of dissociated ions, so corrosion occurs much faster in salt water than in distilled or tap water.[8]

  • What implications arise from your results?
READ
Iron: Element, Formation, Uses

Because this experiment proved that iron oxidizes faster in ocean water than in distilled water, and that even in the distilled water iron oxidized quickly, any metal that is going to be exposed to ocean water should be protected to prevent rust from forming. Anything that prevents the movement of electrons can help to prevent oxidation.[9]

Conclusion

This lab was quite successful. The hypothesis made was proven to be correct, that the ocean water would oxidize the iron faster than the distilled water would, but for different reasons than predicted. The results produced were dramatic and informative, and this lab was simple to perform. Some things to be done differently in the future would be to pay careful attention to the amount of each substance being added to the ocean water, and to measure the amount of precipitate formed in each beaker, as there was much of it in the ocean water beaker. This lab highlighted the importance of preventing oxidation of rust not just to prevent mishaps with products but to prevent the spread of tetanus. Preventing the formation of rust can be done using paint, by galvanizing metals and using metals that do not corrode easily, and should be made a practice of manufacturers and consumers worldwide.


[1] Rust. (2012). En.wikipedia.org. Retrieved 15 June 2019, from https://en.wikipedia.org/wiki/Rust

[2] The Dangers of Rust | Hankey Law Office. (2019). Hankeylawoffice.com. Retrieved 15 June 2019, from https://www.hankeylawoffice.com/articles/the-dangers-of-rust/

[3] Group, A. (2019). Outbreak of tetanus cases following the tsunami in Aceh Province, Indonesia. – PubMed – NCBI . Ncbi.nlm.nih.gov. Retrieved 15 June 2019, from https://www.ncbi.nlm.nih.gov/pubmed/19153905

[4]Rust. (2012). En.wikipedia.org. Retrieved 16 June 2019, from https://en.wikipedia.org/wiki/Rust

[5] Definition of control variable | Dictionary.com. (2019). www.dictionary.com. Retrieved 16 June 2019, from https://www.dictionary.com/browse/control-variable

[6] Definition of control variable | Dictionary.com. (2019). www.dictionary.com. Retrieved 16 June 2019, from https://www.dictionary.com/browse/control-variable

[7] Definition of control variable | Dictionary.com. (2019). www.dictionary.com. Retrieved 16 June 2019, from https://www.dictionary.com/browse/control-variable

[8] (2019). Sciencing.com. Retrieved 16 June 2019, from https://sciencing.com/salt-water-rust-metals-5150093.html

[9] Effect of Sodium Chloride (NaCl) on Rust: Lab Explained. (2019). SchoolWorkHelper. Retrieved 19 June 2019, from https://schoolworkhelper.net/effect-of-sodium-chloride-on-rust-lab-explained/

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