Why Metals Rust: Chemistry Experiment on Liquid Corrosion

Purpose and Hypothesis

Rusting is considered to be an oxidation process in which a chemical reaction takes place. The metal reacts to the liquid poured over it — for example, water — in which oxygen creates a reaction on the metal surface, causing it to rust. Initial experiments by professors indicated that the investigation conducted by Grace Calvert in 1871 showed the first stage of rusting due to the presence of carbonic acid and its conversion to atmospheric oxygen, since it is inherent in the moisture (Nature, 1906). Later, in 1898, another chemistry expert revealed that pure oxygen in water attacks iron, producing ferrous oxide and hydrogen peroxide. A portion of the hydrogen peroxide converts ferrous oxide into rust, while the remainder comes into direct contact with the iron, manifesting as corrosion.

The goal of this research is to evaluate which liquid causes metal to rust the fastest. For this purpose, the following hypothesis is formulated:

If water, orange juice, coke, apple juice, and vinegar are tested to determine which liquid will cause rust most quickly, it is hypothesized that orange juice will rust metal the fastest, because it is the most acidic and carries the greatest amount of acid.

Background Discussion

Have you ever wondered why nails rust, or how rust is formed? To answer these questions, it is useful to examine what types of liquids cause rust. Various metal objects — such as slates, bikes, and tools — are destroyed by rust. To prevent these objects from rusting quickly, a variety of liquids can be observed for their reaction to metal, helping to decipher how and what causes metal objects to rust. Researchers have established that rust is a compound of iron oxide hydrate. Iron oxide is a chemical compound, and corrosion is a primary example of rusting (Grafen et al., 2000).

Research from earlier times suggested that rust occurs only under certain conditions. Iron is unlikely to rust when carbonic acid is absent (Nature, 1907). However, it was observed that even when careful precautions were taken to exclude carbonic acid, the chemical reaction of liquid water and oxygen on iron still caused rust. It was assumed that alkalis could have contributed to rust production even without carbonic acid. Another finding showed that when polished iron was immersed in a solution of potassium dichromate, the rusting process was absent and the surface of the iron remained intact (Nature, 1907).

Different conditions determine whether and how rust forms on metal. The surface finish of steel or iron nails produces different corrosion outcomes. For example, a common nail will continue to rust when exposed to air or water, as a layer of hydrated rust becomes visible over time (Lee, 2007). Electro-galvanized nails coated with zinc are less vulnerable to corrosion than hot-dipped nails. The coating on the nail protects the iron from rusting and prolongs the iron's holding power. A vinyl coating extends this protective effect, since oxidation does not occur as easily on a coated metal surface.

An investigation was conducted to determine whether rust can be transferred from one surface to another; the results showed that such transfer is impossible (Micallef, 2019). Even in a jar full of rusted nails, shaking the jar may damage the surfaces of the rusted nails, but rust cannot be transferred from one surface to another. If polished nails are placed in the same jar, their surfaces may be scratched by rubbing against the rusted nails — making them more susceptible to future rusting — but the experiment itself revealed no rust forming in the absence of water or through contact alone.

Waldman (2016) stated that exposure to dampness in the air creates rust. The production of hydrated oxide results from the reaction of oxygen with water present in the air. Rust cannot occur in dry air; it always requires moist air or the presence of liquid water. The chemicals oxygen, iron, and water together create rust. Carbon dioxide (CO₂) combines with iron, oxygen, and water to form carbonic acid, which reacts in a way that breaks down the iron. This breakdown is initiated by hydrogen, oxygen, and water.

The chemical reaction that causes corrosion results in the breakdown of metals, which is visible as rust. Holleman and Wiberg (2001) explained that to prevent rust, iron should be isolated from both water and air.

Materials and Methods

The materials required for the experiment include the following:

The procedure for the experimental research — determining which liquid is most acidic and has the highest probability of causing rust on steel nails — is as follows:

Step 1: Label the test tubes with numbers and place them on the test tube rack. The numbers are assigned as follows: 1 for water, 2 for coke, 3 for apple juice, 4 for orange juice, and 5 for vinegar.

Step 2: Place one nail in each empty test tube.

Step 3: Pour each liquid into its corresponding numbered test tube.

Step 4: Record which liquid is poured into which numbered test tube.

Step 5: Keep a record for fifteen days of the condition of the nail in each liquid and each numbered test tube, analyzing reactions in the journal.

Step 6: Chart the results for each liquid and its reaction on the steel nails across all test tubes.

Step 7: Transfer the data onto a graph for a clearer demonstration of the findings.

References

Grafen, H., Horn, E., Schlecker, H. & Schindler, H. (2000). Corrosion. Ullmann's Encyclopedia of Industrial Chemistry. Wiley-VCH: Weinheim.

Hamzat, A. K., Adediran, I. A., Alhems, L. M. & Riaz, M. (2020). Investigation of corrosion rate of mild steel in fruit juice environment using factorial experimental design. International Journal of Corrosion, 2020.

Holleman, A. F. & Wiberg, E. (2001). Inorganic chemistry. Academic Press.

Lee, M. (2007). Research question: How do the finishes of iron nails and the presence of water affect their rusting rates? CSUN.

Micallef, C. (2019). Can rust spread through temporary contact? Innovations in Corrosion and Materials Science, 9(1), 60–65.

Nature. (1906). The rusting of iron. https://www.nature.com/articles/074116a0.pdf

Nature. (1907). Letters to the editor: The rusting of iron. https://www.nature.com/articles/075390d0.pdf

Pietrucha-Urbanik, K., Skowronska, D. & Papciak, D. (2020). Assessment of corrosion properties of selected mineral waters. Coatings, 10(6).

Thirumalai, M., Bosco, B., Jesuraja, P. & Paulraj, S. (2020). Effects of salt, vinegar, and bleach in accelerating rusting of iron. International Journal of Innovative Research and Advanced Studies, 7(6), 20–26.

Waldman, J. (2016). Rust: The longest war. Simon & Schuster.