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Question 1
How many atoms are in 37 grams of Oxygen?
Step 1 : Read the question and identify the starting point and
the final destination.
In this case the starting point is 37 grams of Oxygen and the final destination is atoms.
Step 2 : Using your “Mole Road Map,” determine how many
fractions (not including the starting point) it will take to get from
the starting point to the final destination.
In this case, it will take two fractions to get from the starting point to the final destination.
Mass (g) Moles Atoms
(^12)
Step 3 : Take your starting point and place it over 1.
37 grams of Oxygen 1
Step 4 : Multiply between fractions and make sure that the unit
on the bottom of the new fraction is the same as the unit on the
top of the previous fraction.
37 grams of Oxygen x _________________ 1 grams of Oxygen
Step 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 stop is at moles; therefore, you want to create a relationship between grams of Oxygen and moles of Oxygen. Whenever you create a relationship between grams and moles, it is necessary to use your periodic table to determine the molar mass. If this were a molecule (i.e. – H 2 O) it would be necessary for you to use your periodic table to calculate its molar mass.
37 grams of Oxygen x 1 mole of Oxygen 1 16 grams of Oxygen
Step 6 : Create a relationship between the first stop and the
final destination.
In this case it is necessary to create a relationship between moles of Oxygen and atoms of Oxygen. Whenever you create a relationship between moles and atoms (molecules, particles, etc.) it is necessary to use 1 mole = 6.02 X 10^23.
37 grams of Oxygen x 1 mole of Oxygen x 6.02x10²³ atoms of Oxygen 1 16 grams of Oxygen 1 mole of Oxygen
Step 7 : Cancel all possible units. This should leave only the units
that represent the final destination.
37 grams of Oxygen x 1 mole of Oxygen x 6.02x10^23 atoms of Oxygen 1 16 grams of Oxygen 1 mole of Oxygen
Step 8 : Multiply all numbers on the top. Multiply all numbers on
the bottom. Divide the product of the top by the product of the
bottom.
(37))(1)(6.02x10^23 atoms of Oxygen) = 2.23x10^25 atoms of Oxygen = 1.39x10^24 atoms of Oxygen (1)(16)(1) 16
Step 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 2 O and grams of H 2 O. Whenever you create a relationship between grams and moles, it is necessary to use your periodic table to determine the molar mass. Since H 2 O is a molecule it is necessary for you to use your periodic table to calculate its molar mass as opposed to just locating its molar mass on the periodic table.
HÆ 2 atoms x 1 amu = 2 amu or 2 grams/mole
- O Æ 1 atom x 16 amu = 16 amu or 16 grams/mole
H 2 O has a mass of 18 grams/mole
2 moles of H 2 O x 18 grams of H 2 O 1 1 mole of H 2 O
Step 6 : Cancel all possible units. This should leave only the units
that represent the final destination.
2 moles of H 2 O x 18 grams of H 2 O 1 1 mole of H 2 O
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 2 O) = 36 grams of H 2 O = 36 grams of H 2 O (1)(1) (1)
