Rusting Rates of Iron Nails

Author(s): Miha Lee
Growth & Development Experiment
SED 695B; Fall 2007

Research Question: How do the finishes of iron nails and the presence of water affect their rusting rates?

Standards addressed:Chemistry

Grades Nine Through Twelve
3. g.* Students know how to identify reactions that involve oxidation and reduction and how to balance oxidation-reduction reactions.

8. Chemical reaction rates depend on factors that influence the frequency of collision of reactant molecules. As a basis for understanding this concept:

a. Students know the rate of reaction is the decrease in concentration of reactants or the increase in concentration of products with time.

b. Students know how reaction rates depend on such factors as concentration, temperature, and pressure.

Independent variable
Dependent variables
  • Kind of Nails (Finishes)
  • Nails' Mass
  • Temperature (80F)
  • Time (10days)
  • With water
  • Without water
  • Three kinds of nails
  1. Bright nail
  2. Coated nail
  3. Galvanized nail
  • Six testtubes
  • One testtube stand
  • Calcium chloride
  • Electrical balance
  1. Meausre the mass of two nails of each kind.
  2. Put the nails into the testtubes.
  3. For the series of 'Immersed', fill the testtube half with tab water and measure the total masses.
  4. For the seiries of 'Dry', wrap a small amount of calcium chloride with a piace of tissue, and then put the tissue into the mouth of the testtubes.
  5. Allow the testtubes to rust for two weeks.
  6. After two weeks, mesuare the change in the mass of each nail.
  7. Calculate the rates of each nail's rusting by dividing the the changes in mass by the time(day).

Background Information

1. Purpose of the Experiment

  • to know how to measure a reaction rate.
  • to know what affects the reaction rate.
  • to know how to prevent rusting

2. Chemistry of Rusting Iron.

Rust is a general term for iron oxides formed by the reaction of iron with oxygen. Several forms of rust are distinguishable visually, and form under different circumstances. The chemical composition of rust is typically hydrated iron(III) oxide (Fe2O3.nH2O), and under wet conditions may include iron(III) oxide-hydroxide (FeO(OH)). Rusting is the common term for corrosion of iron and its alloys, such as steel. Although oxidation of other metals is equivalent, these oxides are not commonly called rust.

Pure, solid iron oxidizes in water:

Fe(s) -> Fe2+(aq) + 2e-

These electrons will quickly react with the disassociated hydrogen ions (in H3O+(aq) form) and the dissolved oxygen in the water (O2(aq)):

4e-(aq) + 4H3O+(aq) + O2(aq) -> 6H2O(l)

Therefore, as seen from the above equation, the more acidic the water, the greater will be the rate of corrosion (since the concentration of H3O+(aq) will be greater.) At extremely low pH’s, the hydrogen ions will react with the electrons producing hydrogen gas instead:

2H+(aq) + 2e-(aq) -> H2(g)

Thus, as seen from the above equations, the pH of the solution (whether it is pure water or water containing electrolytes) rises. This leads to the formation of OH- ions (in cases where the body of water is significantly large, the pH does not rise as sharply, but this is of no consequence since OH- ions are always present, even in pure water.) The cations then react with the OH- or even the H+ ions and dissolved oxygen to form a variety of compounds, which constitute rust:

Fe2+(aq) + 2OH-(aq) -> Fe(OH)2(s)

4Fe2+(aq) + 4H+(aq) + O2(aq) -> 4Fe3+(aq) + 2H2O(l)

Fe3+(aq) + 3OH-(aq) -> Fe(OH)3(s)

From the above equations, it is seen that the pH and amount of dissolved oxygen can affect the outcome of the reactions. In water with limited dissolved oxygen Fe3O4(s) is formed, which is a black solid and commonly called lodestone:

6Fe2+(aq) + O2(aq) + 12OH-(aq) -> 2Fe3O4(s) + 6H2O(l)

The porous Fe(OH)3 rust can slowly disintegrate into a crystallized form, which is the familiar red-brown rust:

2Fe(OH)3(s) -> Fe2O3•H2O(s) + 2H2O(l)

3. Rust Prevention => Finishes

Name Photo Feature
Common nail Bright common nails have no finish. They can cause rust streaks if they are used in siding or decking. Hydrated rust is permeable to air and water, allowing the metal to continue to corrode - internally - even after a surface layer of rust has formed. Given sufficient hydration, the iron mass can eventually convert entirely to rust and disintegrate.
Galvanized nail A common way of making nails corrosion-resistant is to coat them with zinc. Hot-dipped (H.D.) nails have been galvanized by dipping them in molten zinc. Electrogalvanized nails are plated with zinc, and are not as corrosion-resistant as hot-dipped nails. A third process peens zinc onto the nail. By roughening the nail's surface, all these treatments–but especially hot-dipping–increase the holding power of the nail. These rely on the zinc oxides protecting the once-scratched surface rather than oxidizing as a sacrificial anode. In this picture, the silver color is zinc. The rust of zinc is white.
Vinyl coated nail Corrosion control can be done using a coating to isolate the metal from the environment such as air(oxygen) and water. Paint, wax, vinyl and cement are commonly used substances for coating. Vinyl coating also provides greater holding power. In this picture, the yellow color is caused by the vinyl coating. However, the state of coating was not even resulting in uneven rusting.

4. Reaction Rate

Reaction rate is a measure of how fast a chemical reaction takes place. We usually express the reaction rate in terms of how fast a product is produced or how fast a reactant is consumed. The reaction rate of a general chemical reaction, aA + bB → pP + qQ, can be defined as:


For rusting, it is difficult to write an equation due to the complexity of the reaction. Thus, we can express the reaction like the following.

Iron + Oygen → Iron oxides (rust)

4Fe + 3O2 → 2 Fe2O3

According to the law of conservation of mass, the increased mass of nail and rust is the amount of oxygen.

Rusting rates = [the increased amount of product] / [time]

= [the consumed mass of oygen] / [time]

= [Nail's Change in mass] / [time in the unit of days]


Results and Discussion


Nails Finish Water Initial Mass
Final Mass
Change in mass (g) Rusting rate
1 no finish yes        
2 no        
3 vinyl coated yes        
4 no        
5 galvinized yes        
6 no        

The masses of nails aer to maesure before and after the treatment.

After treatment, you need to include the mass of rust in the final mass.





Initial Mass

Final Mass

Change in mass (g)

Rusting rate


no finish













vinyl coated

























To compute the rusting rates, you need to divide the change in mass by the time, here 10days.


As you can see, without water rusting doesn't take place in any cases.

Water acts like a catalyst in the reaction of oxidation of iron to get rusted.

The finishes prevent iron nails from rusting.

Espeically, galvanized nail lasts longer than coated mails.


Day Common Vinyl coated Zinc galvanized


With your naked eye, you can detect the differences in rusting rates.

After immersing the nails for a few hours, you can see rusts on the nails.

To compare the rusting rates, you can use the height of rust, but the data is too rough.

Galvanized nail has a white rust on it. The white rust must be zinc oxide, not iron oxide.


    My original intention was to measure the changes in mass everyday, but the changes in mass were unstable to be used as data. The absorption of water vapor from the atmosphere made the 'without water test tubes' heavier without rusting. In addition to this, the evaporation of 'water test tubes' caused some decrease in their masses. Thus, I decided to compare the mass only between before and after the treatment. The result proved that water is an important substance in the process of rusting and that the finishes help keep the nails from rusting.

However, if you want to carry out qualitative experiment, this is a good and reliable method.

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