Students will use the rusting model to investigate the factors that affect the rate of rust formation. Each group selects a variable to investigate, analyze their results, make a conclusion, and present their findings to the class with evidence from their model. 

You will need the following resources to complete this assignment.

• NetLogo Rusting Reaction Presentation Rubric

If you ride a bike, you might have noticed how important it is to not leave your bike outside, especially in the rain. If you do, parts of your bike will begin to rust. When enough rust has built up on the moving parts of the bike (like the chain or wheels), it can make it very difficult to pedal. Rust is a brownish-orange substance that you can find on certain types of metal objects. 

Rust is a substance that forms from a chemical reaction with iron and oxygen. Any iron object that is exposed to oxygen might rust over time. When an iron object turns to rust, the rusted object is weaker and more brittle than the iron it used to be made of. But it is rare to find a pure iron object these days. Iron is typically used to make things like tools, cooking equipment, weapons, and farming machinery. Steel, however, is also used to make lots of objects, and steel is made of mostly pure iron atoms, with a small amount (around 5% or less) of carbon atoms in it. Since steel is mostly made of iron atoms, it rusts too! Think of all the steel objects you have seen outside that you have found rust on. 

In this investigation you will be use NetLogo models to simulate and visualize the molecules involved in this chemical reaction.

1. Set the INIT-GAS-TEMPERATURE to 50.
2. Set the NUMBER-OXYGEN-MOLECULES to 50.
3. Set the ACTIVATION-ENERGY to 100
4. Set the IRON-BLOCK-GEOMETRY to 9x9 Middle Box
5. Press the SETUP button
6. Press the GO/STOP and observe the molecules in the model.

You should now be able to recognize oxygen molecules and carbon molecules in the model.

It can be a bit difficult to see how many atoms are in each rust molecule. The molecule should look like it has oxygen atoms and iron atoms in it. To clearly see how many of each of these atoms are in a rust molecule, you will need to see where the boundary of one molecule ends. 

1. Set the IRON-BLOCK-GEOMETRY to 9x9 Middle Box

2. Press the SETUP button

2. Press the GO/STOP

3. Press TOGGLE RUST MOLECULE BOUNDARIES

4. Observe the molecules in the model.You can use the model to help you visualize the boundaries of the rust molecules.

Now that you can see that a single molecule of oxygen is made of three oxygen atoms and two iron atoms, repeat exploration 2 to check and see if only a single molecule of rust is created when a reaction occurs between the reactants.

1. Set the IRON-BLOCK-GEOMETRY to 9x9 Middle Box

2. Press the SETUP button

2. Press the GO/STOP

3. Adjust the slow motion slider to study this prediction.

Let the model run until most of the edges are covered in rust. 

In reality, iron or steel only rusts on the surface. Over time, however the rust sometimes flakes off the surface, exposing more iron or steel underneath to the air.

To mimic what happens in reality, when rust flakes off the surface of iron or steel, do the following.

1. Set the IRON-BLOCK-GEOMETRY to 9x9 Middle Box

2. Press the SETUP button

2. Press the GO/STOP

Let the model run until most of the edges are covered in rust.

3. Press the USE MOUSE button (it will stay black when pressed once)

4. Set the MOUSE-INTERACTION chooser to [drag away rust]

5. Then, using your mouse, left click and hold the button down when you point at a rust molecule. With the button on the mouse pressed down, drag the rust molecule away from the iron block. 

In reality, the rusting process does not occur very quickly. In the model, the current setting for ACTIVATION-ENERGY of 400 is too low. The low setting of this slider is to help show you how rust would react if it required a small amount of kinetic energy to occur. 

1. Set the IRON-BLOCK-GEOMETRY to 9x9 Middle Box
2. Set the ACTIVATION-ENERGY slider to 200.
3. Press the SETUP button
4. Press the GO/STOP 
    
5. Answer Question 6.1
6. Set the MOUSE-INTERACTION button to [shine UV light on iron]
7. Then use the computer mouse to click and hold the button down on a location where there are iron molecules. 
8. Answer Question 6.2

1. Set the ACTIVATION-ENERGY slider to 400.
2. Press the SETUP button
3. Set the MOUSE-INTERACTION button to [add water]
4. Then use the computer mouse to click and hold to paint water on one edge of the iron block. The picture here shows what this would look like after you painted water on the top edge of the iron block:

5. Press the GO/STOP

Watch what happens.

In Exploration 5, you should have seen that speeding up the gas particles can help provide enough energy to the reactants so that rusting can occur. Before you sped up the gas particles, and had a high activation energy for the reaction, the reactants did not have enough energy to react. This is similar to what happens in reality. Oxygen and rust can be made to react with high energy when they are bombarded with ultra-violet (UV) light. Scientists believe that this is one reason why the surface of the planet Mars is covered in particles of rust. The visible surface of Mars that is brownish-orange is due to the vast amount of rust on the surface. 

In many types of chemical reactions, there is sometimes more than one way to get a chemical reaction to occur. Sometimes the reactants can be made to react more easily when they are in the presence of another molecule. In Exploration 6, you saw that the water helped the rusting reaction occur. This process also happens in reality, as the addition of water allows the atoms to move through a series of steps that require less energy, rather than going directly into making energy. This method of transforming reactants over a series of steps is referred to as a chemical pathway. The details of what happens in that pathway are not important right now. Instead, you should recognize that water decreases the amount of energy required to turn oxygen gas and iron into rust. 

Water is not used up in the chemical reaction for rust, it is simply a catalyst. A catalyst is a chemical substance that increases the rate of reaction without being consumed. The catalyst lowers the activation energy required, allowing the reaction to proceed more quickly or at a lower temperature.

In the computer model you should see that there is a chooser called IRON-BLOCK-GEOMETRY. The chooser has options that allow you to change shape and size of the iron block. If you look at the rest of the interface, you will see there also the other widgets that let you control initial temperature, activation energy, water location, etc.

Design an experiment to test a question that you would like to investigate with this model AND that you think the model is capable of helping you investigate. 

Be sure to run your experiment after answering questions 9.1 and 9.2.