Project: Corrosion of Iron

Transcription

1 Project: Corrosion of Iron Potential Credits: /15 Name: Goal: The goal of this lab is to help you acquaint you with the process of corrosion and to investigate how it can be slowed. You will be provided with data from an experiment in which Iron nails were placed in test tubes containing various solutions and/or other metals and asked to analyze this data. Finally you will be asked to answer some questions about the results and concepts. Iron and Corrosion Research Questions: Google and/or Wikipedia will be helpful in answering these questions. 1. Iron is the fourth most abundant element by mass in the earth's crust after oxygen silicon and aluminum. Iron is the second most abundant metal after aluminum. However it is more widely used than aluminum. Find a reason why this is the case. 2. Most iron is converted into steel before use. Which other element is most commonly alloyed with iron to create steel? 3. What is the biggest drawback of using Iron over Aluminum? Hint: Check the title of this project! 4. What are the two common oxidation numbers of iron? 5. What does it mean to "galvanize" iron? 6. What is the common name for the substance formed when Iron corrodes? Hint you see it on old cars. Page 1 of 6

2 Procedure: NOTE: You do NOT need to actually do this experiment. The procedure is presented here for your information and you will be given the results below. 1. Eleven regular iron nails are placed in test tubes. One galvanized iron nail is also placed in a test tube and they are labeled 1 through Various solutions are added to each test tube as shown in the data table. 3. The first observation is made 5 days later. The second observation is made 5 days after the first observation. An example of what this might look like is shown in the picture below: Page 2 of 6

3 Data Table: Number Contents First Observation Second Observation Amount of Corrosion (Larger Number indicates more corrosion) 1 Filled with Water (Control) Some Rust More Rust 5 2 Half Water, Half Air Some Rust More Rust 7 3 Filled with 0.05 M NaCl (Table Salt) Some Rust More Rust 8 4 Filled with 0.05 M HCl Yellow Solution Yellow Solution Filled with 0.05M NaOH No Change No Change 1 6 Air only No Change No Change 1 7 Boiled Water (Air has been removed from the water) No Change Tiny amount of rust 3 8 Zinc wrapped around nail. Filled with water No Change Tiny amount of rust 3 9 Magnesium wrapped around nail. Filled with water. No Change Tiny amount of rust 2 10 Copper wrapped around nail. Filled with water Some Rust More Rust 8 11 Grease coated nail. Water No Change No Change 1 12 Galvanized nail. Water No Change No Change 1 Page 3 of 6

4 Analysis: 1. When you compare test tube 6 to test tube 1 it should be obvious that water is necessary for corrosion. Compare test tube 7 to test tube 1, what else is required for corrosion? 2. Specifically, what component of your answer above is required for corrosion? 3. Look at the results from test tubes 1, 3, 4 and 5 and rank salt, base, acid and water in terms of how much they increase corrosion. 4. The corrosion of iron is a multi step process. The first step is to oxidize Iron into Iron(II) ions. Look this up on the Standard Reduction Potentials of Half Cells chart in your data booklet and record the reaction and the E o value below. As this is an oxidation reaction you must reverse the sign on the E o value. 5. A redox reaction always requires both oxidation and reduction. This means we need an oxidizing agent. In this case that agent is the answer to question 2. There are two equations for the reduction of this element from the Standard Reduction Potentials of Half Cells. One in neutral water (10-7 M), one in 1 M acid. Write these reactions below with their E o values. 6. Which of the above reactions will proceed more quickly, acid or neutral water? Explain. Does this agree with the results from the experiment (test tubes 1 and 4)? 7. Iron(II) ions can be further oxidized to form Iron(III) ions. Write this oxidation reaction with its E o value below. Page 4 of 6

5 8. The reduction reaction in this experiment uses up H+ ions. This produces OH- ions in solution. What you see as rust is a precipitate that forms between Iron(III) ions and hydroxide ions. Write this reaction below. 9. Compare the results for test tubes 8,9 and 10. Which metal(s) slowed corrosion and which metal(s) hastened corrosion? 10. Explain the above results using the Standard Reduction Potentials of Half Cells table in your data booklet. 11. Explain the results of test tube Explain the results of test tube 12. Page 5 of 6

6 Further Investigation: 1. Blocks of magnesium are connected at intervals to hulls of ships to prevent the corrosion of iron. They are called "sacrificial anodes" since they sacrifice themselves to prevent the iron from corroding but this means they need to be replaced periodically. Why does it make economic sense to replace the blocks of magnesium? 2. As opposed to magnesium, galvanized objects do not need their metal replaced. Do some research and determine why this is so. 3. Explain why the salts put on winter roads to melt ice can hasten the corrosion of a car. 4. Some tools made of iron are not able to be plated. Based on your results can you suggest a method of protecting these tools when they are stored? Page 6 of 6