Effects of salt and other contaminants on rate of rusting

Introduction: (Initial Observation)

Rusting is one of the most common ways of corrosion that damages and destroys metal structures such as cars, pipes, tanks, bridges and factories.
Rusting often creates side hazardous as well. For example rusted tanks and pipes leak and contaminate the soil, also rusted equipment break and put human life in risk.
Every year billions of dollars is being invested on research and technologies to prevent rusting and other types of corrosion. Research on factors that may prevent, slow down, or accelerate rusting has been done for many years. In this project our focus is to find out the effect of salt and other contaminants on rusting.

Please select only one of the experiments for your project.

Information Gathering:

Find out about rusting. Read books, magazines or ask professionals who might know in order to learn about the factors that affect rusting. Keep track of where you got your information from.

Rusting is oxidation of iron or steel while exposed to air and water. (Steel is an iron alloy. In order to give strength and some other properties to Iron, they mix it with small amounts of carbon and other metals such as nickel and chromium. The result is known as steel. There are many different types of steel! specially some are very resistant against corrosion.) The most common way to prevent rusting, is coating the surface of iron with paint or any rust resistant metal. Metals such as Zinc and chromium do not rust. You may ask, why don’t we just use metals who don’t rust? The answer is that some of those metals such as chromium are rare and expensive, and some others such as zinc do not have the strength needed for heavy structures such as buildings. A metallic coating or paint keeps moisture and air away from iron surface so it will not rust.

Experiments have shown that oxygen alone does not cause rusting. Rusting is a chemical reaction between oxygen and iron that needs water presence as a catalyst.

Dear

You will need to do additional search on the Internet for keywords such as Rust Prevention or Rust causes. You may find some titles related to rust in vegetations that is kind of disease for plants, just ignore them and focus on rusting Iron or just search for Iron Rust. If you have any questions, click on the help above to send me a message.

Thanks

Project Advisor

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Do contaminants such as table salt, detergents and other household solutes affect in the rate of rusting? Can we find contaminants that slow down the rusting of iron?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

The independent variable (also known as manipulated variable) is the type of contaminant.

Dependent variable is the rate of rusting that can be observed and measured as color change or weight loss of test samples.

Constants are the type, size and initial condition of test samples.

Controlled variables are light and temperature; so, we make sure that all of our experiments are performed in identical light and temperature conditions.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

I think that the effect of contaminant on the rate of rusting varies based on the contaminant chemical structure. For example detergents may actually slow down the rate of rusting. Detergents such as soap are made from fatty material. Oily structure of fatty molecules may be able to cover the iron and protect it from rust.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1: Rusting nails or wires

Procedure:

Cut 11 same length black iron wire. Depending on the gage (thickness) of wire, each piece can be 2 to 10 feet. Wash them to remove any existing rust or oil from the surface of the wire. It is good if all wires are the same length and the same weight. When wires are washed and completely dry, weigh them all, and record the weights.

Wrap the wires in identical coils so they can feet in the cups.

Keep one wire outside (or place it in distilled water) as your control experiment and do nothing with that.

Prepare 10 beakers, one with 250 ml distilled water and nine others with 250 ml distilled water or tap water. To each of the 9 beakers add 10 grams of contaminant from your list. Stir them until they fully dissolve.

Place your 10 wire coils in 10 beakers in a way that parts of the wire are over the surface (most rust will form close to the surface of water).

Because the natural amount of minerals in tap water are so small in relation to the amount of contaminant that we use, we can simply ignore them. That is why we can use tap water in 9 of our beakers.

Leave the samples for about 2 weeks. Make daily observation to assess the amount of rust in different samples and record the results.

After two weeks the amount of rust in all samples must be measured. This can be done by washing and drying and weighting the samples again. The weight loss is caused by rust. Another method of measuring the amount of rust, is filtering, drying and weighting the produced rust.

In the left picture, I have used a nail to test rusting. Rust will cause discoloration of water and will precipitate. The rate of discoloration and the amount of precipitation can be visually examined and used to determine the rate of rusting. However this method is not very accurate.
Picture in the right shows using a long wire for rust experiment.

I used coffee filter to filter the rust in order to dry and weight them. Dried filter with iron rust is weighted and compared with a dry and clean filter paper. The difference is the weight of iron oxide.

Need Quick Results?

It will take a long time for iron wires and nails to rust. Most rust will form at the part of metal close to the water surface. To make quick measurable results, you may use steel wool instead of iron nails or wires.

Your results table may look like this:

Finally use your results table to draw a bar graph. Each bar represents one substance. The height of the bar represents the weight loss or the rate of rusting.

Experiment 2: Rusting of steel wools

Introduction:

Steel wools have a high surface area and can produce high amounts of rust in a few days. Steel wools are made of iron plus small amount of carbon and other metals. When iron rusts, it forms a compound with oxygen. Every atom of iron can get one oxygen atom. The more rust forms on the steel wool, the heavier it gets. In this experiment we will keep the rust with the steel wool and use the weight increase to determine the rate of rusting.

Procedure:

1. Make a series of 9 mixtures of varying contaminants and water, all with the same concentration of contaminant, for example 25 grams per liter.
2. Keep one separate sample of pure distilled water.
3. Put each mixture in a spray bottle. Also put the distilled water in another spray bottle. Label the contaminant of each spray bottle.
4. Get 11 steel wool pads, place each pad on a separate piece of filter paper and number the papers from 1 to 11.
5. Weigh each pad with the paper and write the initial weight on your data table. Also decide which contaminant will be used for each of the steel wool pads. The 11th steel wool pad will not be sprayed with any liquid. It will be the control.
6. Every day spray each steel wool pad with the proper liquid. Spray the same amount of liquid on each pad. For example you may pump the spray bottle 3 times on each steel wool pad. If the weather is warm, you may repeat spraying more than once a day.
7. After 7 days or 10 days stop spraying water, let all the steel wools dry, weigh them and record the results in your data table. Your data table may look like this:

Please note that in this experiment control is a steel wool pad that we do nothing with that. In other words we do not spray that at all.

In this experiment one of the samples is being sprayed with pure, distilled water with no contaminants.

Make a graph:

You would display your data in a table and a graph. The independent variable, the type of contaminant, goes on the x-axis and the dependent variable, the degree of rusting, goes on the y-axis. To make a bar graph you may make one vertical bar for each contaminant, one for pure water and one for control. The height of each bar represents the weight increase caused by rusting.

Materials and Equipment:

Material that we will use as contaminants are:

Material and equipment we used for experiment 1 are 10 glass beakers, rubber gloves, tools to cut wire and scale or balance. Glass beakers are good because they are clear and very resistant to chemicals and heat. They are also easy to clean and reuse. However plastic beaker, plastic cups or glass cups can be used instead of glass beakers. A small scale or balance can be purchase from a lab supplier (Less than $10) or if you could not find it, use colorimetric method described later.

Material and equipment we used for experiment 2 are 11 steel wool pads, 10 spray bottles, 11 filter papers (coffee filter), digital jewelry scale (about $28 from MiniScience).

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

Please write your calculations in this section of your report.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

Additional questions that can be the subject of other science projects are:

1. Do bacteria affect the rate of rusting?
2. Does PH affect the rate of rusting?
3. Does temperature affect the rate of rusting?

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of References:

http://www.rohmhaas.com/company/plabs.dir/htmldocs/rusting.htm

Question: I did the project on rusting and I noticed that alcohol rusted the most, water rusted but did not stick to the metal, and the metal in the vinegar did NOT rust at all, but the top of the metal that was not in the vinegar DID rust. Why did everything rust the way that it did? Thank you very much.

Answer: Any grease, oil or fat protect iron from rusting, alcohol is able to remove such organic material and expose more of the metal surface to the oxygen. That may have caused a higher rate of rusting with alcohol. Metal inside the vinegar had no rust at all. There are two possibilities for this. It is possible that vinegar has no dissolved oxygen. It is also possible that it did rust, but vinegar dissolved the rust immediately.

A similar experiment

Steel Wool generating heat

Chemical reactions occur every day all around us. A chemical reaction is a process where one type of substance is chemically converted to another substance. The Sun in the sky is one big chemical reaction. The fire in your fireplace is another type of chemical reaction. The smoke that comes out of Dad’s ears when you lose one of his favorite golf clubs is a result of a chemical reaction. OK, so maybe that’s a bad example. This experiment demonstrates a chemical reaction that’s fairly common all around us (and we don’t have to touch Dad’s golf clubs to make this one work).

1. Put the thermometer in the jar and close the lid.
2. Wait about 5 minutes and write down the temperature.
3. Remove the thermometer from the jar.
4. Soak a piece of steel wool in vinegar for one minute.
5. Squeeze the vinegar out of the steel wool pad. Wrap the steel wool around the bulb of the thermometer.
6. Place the thermometer and steel wool back into the jar and close the lid.
7. Wait 5 minutes.
8. Now take a look at the temperature.

What happened to the temperature? Are you surprised that it the temperature rose (sorry this experiment didn’t produce any smoke but then again, you didn’t get grounded either).

The vinegar removes any protective coating from the steel wool, allowing the iron in the steel to rust. Rusting is a slow combination of iron with oxygen. When this happens, heat energy is released. The heat released by the rusting of the iron causes the mercury in the thermometer to expand and rise.

Parent’s Note. Chemical reaction is a process in which one substance is chemically converted to another. All chemical reactions involve the formation or destruction of bonds between atoms . Chemical reactions include the rusting of iron and the digestion of food. Most chemical reactions release heat. For example, chemical reactions that occur in digestion give off heat that keeps our bodies warm and functioning.

Chemists use chemical equations to express what occurs in chemical reactions. Chemical equations consist of chemical formulas and symbols that show the substances involved in chemical changes. The chemical reaction for the rusting of iron shows that four atoms of solid iron react with three molecules of oxygen gas to form two units of solid rust. Experiments demonstrate that iron and oxygen react in these proportions in air at room temperature. Rust is the product, or result, of the reaction. Iron and oxygen are the reactants. The reactants are the substances that undergo chemical change.