Chemistry EEI Introduction: Corrosion is the returning of metals back into their natural constituents when exposed to an atmosphere with which it can react. Both metals and non-metals are able to undergo redox reactions as well as other ceramics and polymers which are known to undergo a similar process which is referred to as degradation. This investigation aims to outline and assess the factors affecting corrosion and explore in depth how redox reactions work. Reduction and oxidization reactions (redox reactions) are responsible for corrosion.
Half reaction equations will be playing a major role in this investigation. (Corrosion technology Australia. 2009) Redox reactions are an exchange of electrons between materials. In a redox reaction there is always an anode (electron donor) and a cathode (electron recipient). The exchange of the electrons can be either in a direct process or can be an indirect transfer of electrons along a conductor from the anode to the cathode. Either direct or indirect, the corrosion will always occur at the anode.
My experiment is aimed at testing the corrosion of 2 different types of nails in a certain molar solution of salt water in anticipation of determining which of the two would be more suitable for beachside residencies. I hypothesized that the iron nails would almost double in content of rust as the molarity of the solution they’re soaked in increases. The galvanized nails hopefully will end up with limited amounts of rust in all solutions. The activity series plays a major role in corrosion itself. The activity series is basically an empirical series of metals; in order of reactivity from highest to lowest.
Gold being the least reactive at the bottom of the list and lithium being the most reactive at the top of the list. Starting at gold and working up to lithium at the top of the list; the metals increase in reactivity, lose electrons more readily to form positive ions, corrode more readily, require more energy to be separated from their ores and finally become stronger reducing agents. The activity series is generally used to summarize information about the reactions of metals with acids and water, single displacement reactions and the extraction of metals from their ores. (Wikipedia. 009) All metals corrode under the right conditions only some more easily than others. As it turns out, the metals that corrode most easily are usually also the most abundant. Corrosion has many factors influencing it. Things such as the environment e. g. climatic conditions, temperature, and humidity all have their say on aiding in corrosion, and as generally all metals corrode under different influences these things are a big factor to consider. Also the types of metal as almost each and every metal corrode differently and to different extents similarly as just mentioned.
The presence of oxygen in water to which iron is exposed increases the corrosion rate also. The reason for this increase is the rapid reaction between oxygen and the polarizing layer of atomic hydrogen absorbed on the oxide layer. (Frank N. Speller. 1934) Variables: Controlled: the controlled variable in my experiment will be the distilled water solution Respondent: the amount of corrosion on each nail in each solution Manipulated: the molarity of each solution of Nacl (aq) Stoichiometric equations relating to investigation:
C=nv Where C = concentration (mol per liter), n = number of moles, v = volume. n=mmm Where n = number of moles, m = mass, mm = molar mass (gmol-1) Half reactions relating to investigation: Oxidization half-reaction of iron in moist air; 2Fe(s)Oxidisation2Fe2+(aq)+4e- E=0. 41V Reduction half reaction of moist oxygen; O2g+2H2Ol+4e-reduction4OH-aq E=0. 40V Overall Reaction; 2Feg+O2g+2H20l 2Fe2+aq+4OH-aq E=0. 81V From the reaction taking place in the above equations the potential difference of iron in contact with air, in a moist environment is 0. 1 volts. As this potential is a positive one, this reaction indicates a spontaneous redox process. Meaning this will be a naturally occurring process. Materials: 1. ) Test tube rack 2. ) 24 test tubes 3. ) 12 iron nails 4. ) 12 galvanized nails 5. ) Distilled water 6. ) Beaker 7. ) Measuring cylinder 8. ) Scales 9. ) Salt Method: 1. Using your stoichiometric equations find the mass of salt that you need for each molar solution. 2. 2. 338g of salt is required for a 0. 4mol solution of Nacl, 3. 506g for a 0. 6mol solution and 4. 675g for a 0. 8mol solution 3. Now dissolve your 2. 38g of Nacl in 100ml of distilled water to make a 0. 4mol solution of Nacl (aq) 4. Dissolve 3. 506g of Nacl in 100ml of distilled water to make a 0. 6mol solution of Nacl (aq) (same molarity as sea water) 5. Dissolve 4. 675g of Nacl in 100ml of distilled water to make a 0. 8mol solution of Nacl (aq) 6. Collect your 100ml of distilled water (control) 7. Label each solution accordingly (e. g. 100ml 0. 4mol salt water, 100ml 0. 6 mol salt water, 100ml 0. 8 mol salt water and 100ml distilled water) 8. Repeat steps 3-7 as you need for both galvanized and iron nails 9.
Place 8 of your test tubes into the test tube rack 10. Add 4 galvanized nails to four of the test tubes and 4 iron nails to the remaining 4 test tubes. 11. Place each of your solutions into the required test tubes (distilled water for both galvanized and iron nails etc) 12. Record observations based on the extent of the corrosion of each nail over a period of one week 13. Repeat steps 1 through 10 14. At the end of the 7 days remove the rust from the nails and test tubes and filter using filter paper 15. Weigh each of the rust products upon completion