Mole Calculations Page 4
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2
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4Step 5: Create a relationship between the starting point and the
first stop. For some problems, the first stop will be the final
destination.
In this case your first (and only) stop is at mass (g); therefore, you want to create a
relationship between moles of H
O and grams of H
O. Whenever you create a relationship
2
2
between grams and moles, it is necessary to use your periodic table to determine the molar
mass. Since H
O is a molecule it is necessary for you to use your periodic table to
2
calculate its molar mass as opposed to just locating its molar mass on the periodic table.
H
2 atoms x 1 amu = 2 amu or 2 grams/mole
+ O
1 atom x 16 amu = 16 amu or 16 grams/mole
H
O has a mass of 18 grams/mole
2
2 moles of H
O x
18 grams of H
O
2
2
1
1 mole of H
O
2
Step 6: Cancel all possible units. This should leave only the units
that represent the final destination.
2 moles of H
O x
18 grams of H
O
2
2
1
1 mole of H
O
2
Step 7: Multiply all numbers on the top. Multiply all numbers on
the bottom. Divide the product of the top by the product of the
bottom.
(2)(18 grams of H
O) = 36 grams of H
O = 36 grams of H
O
2
2
2
(1)(1)
(1)
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