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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
Activity 3 - RustingPurpose: What causes rust?
Brainstorm Rust is a brownish-orange substance that you can find on certain types of metal objects. Here are two objects that have rust on them --->
What other metal objects have you seen rust on?
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________________________Using a brush to scrape rust off a cooking grill.Rust on a iron nail
List some factors that might influence whether rust forms on a metal object:
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
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Overview Rust is a substance that is a product that forms from a chemical reaction between iron atoms and oxygen molecules. If you tested two pieces of iron that were nearly identical, but one was left out in the air and one was put in a container of pure oxygen gas, why would both rust?
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Exploration 1:Question
“What is rust?”
Model Rules
How are oxygen molecules represented in the model (how many atoms are in them as well)?
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How are iron atoms represented in the model?
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
How is water represented in the model?
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Predict
This is the word equation model for the rusting reaction:
iron (solid) + oxygen (gas) ------> rust (solid)
This equation does not describe the number of atoms that are in the reactants nor the product.
How many atoms of iron do you predict will be in a rust molecule? ___________
How many atoms of oxygen do you predict will be in a rust molecule? ___________
Test Your Predictions
1. Open NetLogo. In NetLogo, go to the FILE menu and select MODELS LIBRARY.
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3. Open the Curricular Models folder. Then open the Connected Chemistry Folder. In this folder open the Connected Chemistry Rusting Reaction model.
1. Press SETUP, and then GO/PAUSE to run the model.
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
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3. When you see your first rust molecule form, press the TOGGLE RUST MOLECULES button a few times.
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5. Press GO/PAUSE again so that it is no longer dark, to pause the model.
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8. Record the number of rust molecules, the number of oxygen molecules that remain and the number of iron atoms that remain in the table below.
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10.Press GO/PAUSE again to resume the model (the button will be dark). Run the model until another rust molecule forms. Pause the model when that occurs.
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12.Repeat the previous two steps two more times, recording your observations in the table below each time.
Record Your Observations:
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
Making Sense of Your Data:
Did your results provide evidence to support your prediction? ________
How many atoms of iron are there in a rust molecule? ___________
How many atoms of oxygen are there in a rust molecule? ___________
Follow-up:
Question: Based on the results from the model, how do you predict the mass of a rusted iron block would compare to an iron block that had not rusted? Assume both blocks were the same mass before rusting occurred on one of them. aThe iron block with rust on it would have the same mass as the block without rust.
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
bThe iron block with rust on it would have more mass than the block without rust.cThe iron block with rust on it would have less mass than the block without rust.dQuestion: Briefly describe an experiment you could conduct in lab that would help you determine whether this prediction was correct?
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Exploration 2:Question
“What factors affect the rate of rust formation?”
Choose A Factor to Investigate
Circle one of the following to investigate:
ñHow does the temperature of the air affect the rate of rust formation?ñHow does the amount of oxygen in the air affect the rate of rust formation?ñHow does the shape of the iron object affect the rate of rust formation?ñHow does the size of the iron object affect the rate of rust formation?ñHow does the presence of water on the surface of an iron object affect the rate of rust formation?ñHow does iron exposure to ultra-violet light affect the rate of rust formation?ñHow does removing rust that is formed on an object affect the rate of further rust formation?
Predict
Make a prediction
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
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The factor you selected to investigate should help you choose which variable you intend to change in the experiment and which variables you will keep constant. In the table below put a C next to the variables you intend to keep constant and a V next to the one you intend to vary.
Then fill in the constant values you intend to use for those marked C, and the range of values you intend to use for those marked V.
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
How do you intend to measure the rate of the rusting?
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Test Your Predictions
1. For each of the constant variables (C), set the value of the variable to what you chose in the table.
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
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3. Set the value of the variable you will be changing (V) to one value in the range you chose to explore.
1. Press SETUP, and then press GO/PAUSE to run the model.
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3. Record the rate of rust formation for this condition.
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5. Change the value of the variable you will be changing (V) to a different value in the range you chose to explore.
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7. Repeat the past 3 steps until you have gathered enough data to answer your question.
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Record Your Observations:
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
Discoveries and Insights:
Make a claim that answers the question you chose to investigate:ñ______________________________________________________________________________
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What evidence in the model supports your claim:______________________________________________________________________________
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What particle behaviors and interactions in the model appear to lead to this outcome?ñ______________________________________________________________________________
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
Briefly describe an experiment you could conduct in lab that would help you support or refute your explanation:
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Would the factor you investigated affect the rate of other types of chemical reactions, besides rusting?
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Why or why not?
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Homework 3 - RustingThe computer model you used in class showed you that if the reactants have enough energy, a rusting reaction will occur.
One such way to increase the energy of the reactants is to bombard them 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
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
Question 1: Where do you think the ultra-violet light came from to cause this rust to form on Mars?
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In the model, you saw that the water helped the rusting reaction occur. Water helps rusting occur in by moving the iron and oxygen atoms through a series of chemical reactions, each of which requires less energy than would be required if they converted directly into rust.
For some chemical reactions, there is more than one series of chemical reactions that will yield a product. In some, the reactants can be made to react more easily when they are in the presence of another molecule (such as water).
Water molecules are not used up in the chemical reaction for rust. Water is not a reactant in the reaction. Water is simply a catalyst. A catalyst is a substance that increases the rate of reaction without being consumed. Water helps lower the activation energy required for the rusting reaction. This in turn allows the rusting reaction to proceed more quickly or at a lower temperature.
Salt is also a catalyst for rusting. Salt water increases the rate of the rusting reaction more than fresh water does, because salt in the water further lowers the activation energy required for the reaction to occur.
Question 2: In the computer model, spots where there was water were represented as blue squares. If you wanted to include a representation of water molecules, what would you want the water to look like?
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Connected Chemistry – Unit 2: Chemical Reactions Center for Connected Learning at Northwestern UniversityDraft Copy – for pilot classrooms – do not cite or redistribute without permission Student Book
Question 3: To prevent or slow down rusting, you can cover iron or steel objects with paint. Explain why you think a coating of paint might prevent parts from rusting.
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Question 4: Besides paint, what other some other ways might you prevent an iron grill from rusting?
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