ATOMS OR MOLECULES?

HYPOTHESIS

We are going to do another modeling exercise. This time we are going to model two chemical reactions: hydrogen and oxygen atoms combining to form water and sodium and chlorine atoms combining to form table salt. Then we will mix these two compounds to make salt water. Is this last step a chemical reaction (and why)?

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MATERIALS & EQUIPMENT

3 dishes
3 labels
1 white index card
3 colored index card halves
glue

PROCEDURE

Label 3 dishes for the three substances we will be making: "water", "salt" and "salt water".
Cut the white index card into 12 pieces. These will be hydrogen atoms.
Use the other three colors for the elements: oxygen, sodium and chlorine. Cut each half index card into six pieces.
Label all of the atoms and put each of the elements in a separate pile.
Combine hydrogen and oxygen. Glue the atoms together to make water molecules. The glue is like the chemical bond that really holds the atoms together. LIut the water molecules in the dish labeled "water". This is a compound.
Combine sodium and chlorine. Glue the atoms together to make salt molecules. LIut the salt molecules in the dish labeled "salt". This is a compound.
Now make salt water. Mix the water molecules and the salt molecules in the dish labeled "salt water". Note that you do not glue them together. They form a mixture, not a compound, and so there are no chemical bonds (and therefore no glue) between them.

CONCLUSION

What is salt water, an element, compound or mixture?

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