1.0 OBJECTIVES
- To study the causes of rusting of iron
- To investigate type of reaction involved in rusting of iron
- To suggest how to prevents rusting of iron 2.0 INTRODUCTION 3.1 HYPOTHESES
In this experiment, we predicted that the nail that will rust the fastest is the condition of nail with the presence of water, oxygen and salts.
2.2 THEORY
Rusting of iron is one of the most common and economically destructive form of corrosion. Corrosion causes tens of billions dollars of damage to cars, ships, buildings, and bridges each year. This natural process oxidizes metals to their oxides and sulfides. About 25% of the steel produced in United States each year is for replacing steel in which the iron has corroded. Rust is not a direct product between iron and oxygen but arises through a complex electrochemical process.

The facts concerning the corrosion of iron are as follows : 1) Iron does not rust in dry air; moisture must be present. 2) Iron does not rust in air-free water; oxygen must be present. 3) Iron loss and rust formation occur at different places on the same object. 4) Iron rusts more quickly at low pH (high [H+]). 5) Iron rusts more quickly in ionic solutions. 6) Iron rusts more quickly in contact with a less active metal (such as Cu) and more slowly in contact with a more active metal (such as Zn).
Rusting is a redox reaction in which iron is oxidized and oxygen is reduced. The redox reaction of rusting can be represent with the following equation : 1. Oxidation of iron : 2Fe (s) → 2Fe2+ (aq) + 4e- 2. Reduction of oxygen : O2 (g) + 4e- + H2O (l) → 4OH-(aq)
Overall equation : 2Fe (s) + O2 (g) + 2H2O (l) → 2Fe(OH)2 (s)
Figure 1 shows the rusting of iron.

Figure 1 The Fe(OH)2 formed in the overall reaction then undergoes several additional reactions to form Fe2O3, the familiar orange substance that we call rust. One of the main problems with Fe2O3 is that it crumbles off the solid iron below it, exposing more iron to further rusting. With the present of water and oxygen, an entire piece of iron can rust away. The salts and soap water solution are also added in this experiment to see whether it is also affecting the rate of rusting. By theory, we know that the nail which contains salts solution with the presence of oxygen gives the highest rate of rusting and rust the most. And the rate of rusting is highest in basic medium. 2.3 VARIABLES
Manipulated variables : Different conditions to test the rusting of iron nails
Responding variables : Rusting of iron nails
Controlled variables : Types of nails 3.0 EXPERIMENTAL PROCEDURE 1) Label the test tubes 1-5. 2) Weight the mass of the nails. 3) Fill test tube 1 with 10.0 ml of deionized water and add a nail. 4) Fill test tube 2 with 10.0 ml of boiled deionized and add a nail. Carefully pour a little oil over the surface to prevent air from reaching the water. 5) Mix a 5.0000g of salt with 10.0 ml of deionized water and add the mixture into test tube 3. Add a nail. 6) Put a nail into test tube 4 and add about 2 cm depth of anhydrous calcium chloride granules that will absorb water. Close the test tube with a rubber stopper to prevent any water from getting in. 7) Pour 10.0 mL of soap water solution into test tube 5 then put a nail into the test tube. 8) Set up apparatus as shown in diagram 1. 9) Every 24 hours record observations of the iron nails at a set time for 7 days. 10) Weight the mass of the nails in the first day and the seventh day. Record your observations and results. 11) Calculate the rates of each nail's rusting by dividing the changes in mass by the time (day). Record your data.

Diagram 1 4.0 CHEMICALS
5 iron nails, Anhydrous calcium chlorides granules, Cooking oil, 10.0 ml of deionized water, 10.0 ml of boiled deionized water (15 min boil), 5.000g of sodium chloride (NaCl) 5.0 APPARATUS
Eye protection, 5 test tubes, 1 test-tube rack, Rubber stopper, Forceps, Pen or other means to label test tubes, 10.0 ml of measuring cylinder, electronic balance.

6.0 RESULTS Day | | | | | | | | Test tube | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 1(water + air) | No immediate change | No change | No change | No change | Black dots formed on iron nail | Rust has slowly started forming on the iron nail | More black dots forming on the iron nail | 2(water) | No immediate change | No change | No change | No change | No change | No change | Rust has slowly started forming on the iron nail | 3(salt water) | No immediate change | No change | Black dots formed on iron nail | More black dots forming very slowly | White substance forming on the top of the iron nail | Bottom half of nail is starting to rust | Bottom half of the nail has completely rusted | 4(air) | No immediate change | No change | No change | No change | No change | No change | Rust has slowly started forming on the iron nail | 5(soap water solution) | No immediate change | Black spots have formed on the iron nail | More black dots covering the iron nail | Rust has formed at top of the iron nail | More rust forming | More rust forming | Rust still forming |
Table 1 : Table of conditions of iron nails for 7 days

Test tube | Initial mass / g( Day 1 ) | Final mass /g( Day 7 ) | Change in mass /g | Rate of rusting (g/day) | 1 | 5.0000 | 5.3197 | 0.3197 | 0.04567 | 2 | 5.0000 | 5.0143 | 0.0143 | 0.002043 | 3 | 5.0000 | 5.8590 | 0.8590 | 0.1227 | 4 | 5.0000 | 5.0158 | 0.0158 | 0.002257 | 5 | 5.0000 | 6.1801 | 1.1801 | 0.1686 |
Table 2: Rate of rusting of the iron nail