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Composition of Compounds
Objectives: To visualize what happens when atoms combine to form molecules
To visualize what happens when molecules break apart
To understand that the ratio of the mass of INDIVIDUAL Atoms is the same as the ratio of the masses of GROUPS OF ATOMS
To understand how we can determine the formula of a compound from the masses of the components of the compound
We are imaging that nuts and bolts are two kinds of atoms. When we combine them we are imagining that we have made a molecule. This will help us to visualize real molecules and atoms.
#1 Nuts and Bolts: ***Round all of your masses to the nearest whole number! ***
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Mass of 1 nut
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Mass of 1 bolt
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Ratio of the masses (bolts/nuts)
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Mass of 3 nuts
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Mass of 3 bolts
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Ratio of the masses (bolts/nuts)
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Mass of 5 nuts
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Mass of 5 bolts
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Ratio of the masses (bolts/nuts)
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Summary Questions:
- How do the ratios of the masses (last column) compare to each other?
- Predict the masses of 10 nuts and 10 bolts.
- Predict the ratio of masses of 10 bolts to 10 nuts.
#2 More Nuts and Bolts:
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Mass of 2 nuts
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Mass of 1 bolt
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Ratio of the masses (bolts/nuts)
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Mass of 6 nuts
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Mass of 3 bolts
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Ratio of the masses (bolts/nuts)
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Mass of 10 nuts
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Mass of 5 bolts
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Ratio of the masses (bolts/nuts)
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Summary Questions:
- Compare the ratios of the masses
- Why does this ratio differ from the ratio of the masses of 1 nut and 1 bolt?
- Predict the masses of 20 nuts and 10 bolts. What would the mass ratio be?
#3 Even More Nuts and Bolts:
Mass of 1 bolt AND 2 nuts (bolted together) ____________
Remove the nuts. Now mass the bolt. ____________
Find the difference (mass of nuts) ____________
Divide the mass of the nuts by the known mass of 1 nut. _________
What is the ratio of the number of nuts to bolts? ____________
#4 What? Even More Nuts and Bolts???
- Mass an empty envelope and record its mass on the envelope.
- Make a “molecule" of 1 bolt and several nuts.
- Roll up the envelope so another group can't feel the “molecule”.
- Seal it with a SMALL piece of tape.
- Pass it onto another group.
Summary questions (Answer the following questions using an unknown envelope):
- How many nuts are attached to the bolt? ____________
- Explain how you determined the number of nuts.
Your teacher will now tie this into the invisible world of molecules. You will need to understand the following vocabulary:
Chemical formula empirical formula atomic mass mass ratio subscripts
#5 Select 2 kinds of other objects that are available.
- Mass each kind and record their masses.
- Make a molecule with 2 of one kind of object and 3 of another. Record the mass of the molecule.
- Now find the TOTAL mass of each kind of atom.
- Divide the TOTAL MASS of each kind of atom by the mass of 1 of these atoms.
- Find the ratio of the two numbers you found from above.
Type of Objects (describe)
Mass of Object l ____________
Mass of Object 2 ____________
Total mass of molecule ___________
Formula of Molecule: What is the ratio of the number of Objects 1 and 2 in your molecule: ______
Total mass of all of object 1 _____ Total mass of Object 1 divided by the mass of 1 of object 1: _____
Total mass of all of Object 2 _____ Total mass of Object 2 divided by the mass of 1 of Object 2:_____
Ratio of the two numbers above: ________
Summary questions:
1. Compare the values of the two numbers on the bold lines above.
2. What is the significance of the value of each of these numbers?
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