1. Find out which substances are essential for rusting to occur. 2. Find out how the rusting process can be inhibited and how it can be promoted. Hypothesis:
I predict that air (oxygen) and water are necessary for iron to rust. The nail in water with air will rust while the nails in dry air and in boiled water with no air will not. I also predict that galvanizing the nail with zinc and greasing the nail and painting the nail and electroplating the nail will inhibit rusting. I also predict that adding NaCl to the test tube with water and air will promote rusting of the iron nail. Background information:
Rusting is the chemical reaction between a metal and oxygen in the presence of water. In this case, it is the corrosion of iron. Corrosion is defined as the loss of metallic properties of a metal due to oxidation and it results in them losing strength and electrical conductivity. When iron is in contact with water and oxygen, it will rust. Chemical equation of the rusting of iron: 4Fe+3O2+H20–> 2Fe2O3.H2O There are certain things that will promote the rusting of iron. An example of this is adding NaCl (salt) to the water. When salt is dissolved in water, it is separated into Na+ and Cl- ions. These ions attach themselves separately to the charged parts of the water molecule (H20). When Na and Cl ions are present in water, there is an increase in the ability of the water to carry electrons as there are more ions in the water, therefore the iron will rust faster. There are also many factors that will inhibit the rusting of iron. Examples of this are painting the iron, greasing the iron and electroplating the iron with copper and galvanizing the iron with zinc.
Paint and grease are impermeable so oxygen and water cannot come into contact with the iron as the paint and grease would be in the way. Plating the iron (galvanizing) with zinc can inhibit the rusting process. Zinc corrodes more easily than iron does because it is higher in the reactivity series so the zinc will corrode before the iron does. Electroplating prevents rusting because it creates a barrier between the metal and the oxygen and water. In this experiment, the iron nail will be the cathode in the electrolysis. The nail (the cathode) and a piece of copper (the anode) will be placed into copper sulphate solution.
The copper sulphate will decompose to form positive copper ions and negative sulphateions. As the copper ions are positive, they are attracted to the cathode, where they will collect electrons, become neutrally charged and will build up as a layer of copper on the cathode. The copper from the anode will dissolve in the electrolyte to replace the copper ions, deposited on the cathode. This will create a layer of copper on the iron nail. Calcium chloride granules will be added to the test tube with no water because calcium chloride takes water from the air because of its hygroscopic nature. This means calcium chloride has the ability to attract and hold water molecules from the surrounding environment. Apparatus:
•8 iron nails
•8 test tubes
•10ml measuring cylinder
•30 zinc granules
•2 crocodile clips
•Copper sulphate solution (250ml)
•Piece of Styrofoam
•Pot of nail polish
•NaCl. H20 (sodium chloride solution)
•20 calcium chloride granules
Size of test tubesZinc covering nailAmount of rust on iron nail Time given for rusting to occurNaCl in water
Temperature of waterGrease covering nail
Amount of water (except in test tube without water)Paint covering nail Amount of air (except in test tube without air)Copper covering nail
Oil in test tube
Boiled water in test tube
Results able showing the scale for amount of rust on each iron nail from –5 Scale numberAmount of rust on iron nail
1A very small amount
2A small amount
3A medium amount
4A relatively large amount
5A large amount
Results table showing the amount of rust on each iron nail in different substances and conditions Substances inside test tubeAmount of rust on nail
Water and air and nail5
NaCl and water and air and nail5
Boiled water and oil and nail4
Water and air and nail covered with grease3
Water and air and nail covered with paint1
Water and air and nail electroplated with copper1
Air and calcium chloride granules and nail0
Water and air and nail covered with zinc0
Rust is an orange- brown solid. The data was collected by determining how much orange- brown solid was on each iron nail and in the test tube. The data received supports my hypothesis. The factors necessary for rusting to occur are oxygen and water. This is true because the nails in water and air did rust, while the nail in dry air did not rust. The nail in the test tube containing boiled water and oil was not meant to rust, though it did because of some errors made while setting up the experiment. The nail covered with zinc did not rust at all; this shows that galvanizing iron with zinc stops the iron nail from rusting. Even though there was water and oxygen inside the test tube, the iron nail did not rust because the zinc covering the iron nail reacted with oxygen, thus forming zinc oxide. The zinc oxide reacted with water molecules forming zinc hydroxide, which reacted with carbon dioxide in the air, forming zinc carbonate, which is impermeable and insoluble. This layer protected the iron from corroding. This supports part of my hypothesis.
The nail electroplated with copper rusted very little, therefore this shows that electroplating iron with copper stops iron nail from rusting. The nail electroplated with copper did not rust a lot because the copper created a corrosion-resistant barrier between the iron nail and the oxygen and water in the test tube. This supports part of my hypothesis. The iron nail covered with grease in a test tube containing water and oxygen rusted quite a bit, though this is an anomaly. The nail should not have rusted because the grease was meant to create an impermeable barrier between the nail and the oxygen and water. The iron nail in boiled water and oil rusted a lot, though not quite as much as the iron nail in only water and air. The nail in boiled water and oil was not meant to have rusted, because there was meant to be no oxygen. If the experiment had gone well, there would be no rust on the nail because for rusting to occur, oxygen must be present because iron reacts with oxygen to form iron oxide (rust).
This data found does not fully support my hypothesis because the data was anomalous and will be discussed in the evaluation. Though the data is anomalous, it still half- supports my hypothesis. Even though these nails rusted, they did not rust as much as the nail in just water and oxygen. The nail in dry air did not rust at all because for rusting to occur, water must be present. This is because rust is Fe2O3.H2O. This proves that water is an essential condition for rusting. The painted iron nail also rusted very little because the paint created an impermeable barrier between the iron nail and the oxygen and water. This supports part of my hypothesis. The iron nail in the salt, water and air rusted approximately the same amount as the iron nail in just water and air. If the results of the experiment were taken after just a few days, the iron nail in the salty solution would have rusted more than the nail in the plain solution because NaCl speeds up the rusting process. Since rusting is sped up by the presence of electrons, salty water therefore will speed up the rusting process.
Salt in water will cause the iron to rust more quickly because salt increases the water’s ability to carry electrons, as there are more ions in the water. Because the results were taken a week after the experiment was set up, the iron rusted as much as it could have in both experiments. The data received supports my hypothesis that water and oxygen are the substances essential for rusting to occur. It also supports my hypothesis that painting iron, galvanizing iron with zinc, electroplating iron with copper and greasing iron will inhibit the rusting process. It also supports my hypothesis that NaCl will promote the rusting process. Evaluation:
To make this experiment a fair test, there were quite a few controlled variables. The size of the test tubes were kept the same and the time given for the rusting to occur was the same, and the type of nail was kept the same for each experiment. The same amount of water was put in each test tube (except in the test tube without water) and the same amount of air was in each test tube (except in the test tube without air). This was done to make sure that these factors were not changed, as we were not testing to see if they had an effect on the rusting of the iron nail. There were quite a few problems with this experiment. The nail should not have rusted in the experiment where the iron nail was covered in paint and put in a test tube containing water and air. It rusted a small amount on the top of the nail because when it was being painted, it was held at the top so the top did not get painted. This could be improved by letting the nail dry, then when it is dry paint the bit that was not painted in the beginning. Also, adding a second layer of paint would make the paint less permeable.
The nail should not have rusted in the experiment where the iron nail was electroplated with copper and put into a test tube containing water and air. It rusted a small amount because when electroplating the nail, it may not have been left in the copper sulphate solution for long enough so the layer of copper was not thick enough, and the layer may not have been evenly covered. To improve this experiment, the iron nail could be left in the copper sulphate solution for a longer time. The nail should not have rusted in the experiment where the iron nail was covered with grease and put into a test tube containing water and air, though it rusted a medium amount.
The reason for this could be that the nail was not fully covered in grease, or that the layer of grease was not thick enough. To improve this experiment the iron nail could be covered all over with at least two layers of grease. The nail in the test tube containing boiled water and oil should not have rusted at all, but it rusted quite a large amount. The reason for this could be that the water was boiled a few days before the experiment, so oxygen could have dissolved back into the water. The oil may also not have been viscous enough and there may not have been enough added. To improve this experiment, the water could be boiled on the same day as the experiment, a different, more viscous kind of oil could be used and more oil could be added to the test tube.