Discussion

4.1 Key Findings
From the data collected, it was clearly found that the higher the pH value of the acids we tested, is inversely proportional the rate of rust. The value of the acids vary as there are 3 acids, Hydrochloric, Sulphuric and Citric acid. When the pH value of Hydrochloric Acid is 0.257, the lowest value among the 3 acids, the rate of corrosion is 2258.68mpy, the highest value of the 3 acid.
For Citric acid, we were faced with a weird problem. The weight of the iron increased.
For Sulphuric acid, crystallization occurred.

4.2 Explanation for Key Findings
Rust is a form of corrosion. (Corrosion Clinic, 2015) The lower the pH value of an acid, the faster the metal corrodes. (Ted Mooney, 2015) This is due to oxidation of the iron plates. The iron plates loses weight as the acid eats away layers of the metal. To add on, the higher the molarity of an acid, the higher the pH value. To conclude, the higher the pH value of the acid, the faster the rate of corrosion and the lighter the iron plate will be at the end of the experiment.
The weight of the metal increased, as there was the citric acid residue left after we took it out of the petri-dish.
Crystallization occurred as the sulphuric acid evaporated, and condensed on the iron. The crystal is Iron Sulphate. The sulfur eats away the galvanized layer, hence, allowing the sulfur molecules to react with the iron. (Docbrown, 2015) Therefore, crystallization occurred. (Wikipedia, 2015)

4.3 Evaluation of Hypothesis
Hypothesis: The more concentrated the acid, the more corroded the metal will be and sulphuric acid will corrode the iron plates the most. The hypothesis was proven to be correct and this supported by our data analysis. The sulphuric acid corroded the metal most as it had the lowest pH value compared to the other 2 acids. Hence, this proves our second hypothesis correct. (Wikipedia, 2015)

4.4 Area for Improvement
For our experiment, we could use more commonly used acids, such as Carbonic Acid. Carbonic Acid is common in the sea, as it is formed when Carbon Dioxide is chemically bound with H2O. The acids that we used - Hydrochloric Acid, Sulphuric Acid and Citric Acid, are not commonly found when there is a use of metal. Iron was used as a base metal for our experiment as iron is commonly used for making a ship's hull. However, we could use other metals for the experiment as there are other metals used to make the ship's hull. The duration of the metal that should be left in the acid solution should be longer, as when a ship is sailing, it would sail for more than 25 hours, hence the timing that we used would not be accurate to show effects.

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