Moles and Stoichiometry
By Noah Balla, Justin Panzarino, and Derek Prestera
Key Terms:
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mole(mol): the amount of a substance that contains as many particles as there are
atoms in exactly 12.00 grams of 12C
○ used to convert atomic mass units to grams
molar mass: sum of the atomic masses (in grams) in a molecule
○ unit: g/mol
23
Avogadro’s number:
6.02 x 10
○ number of particles in exactly one mole of a pure substance
22.4 L: This constant is used to convert from moles to volume or volume to moles.
Empirical Formula: A chemical formula that gives the simplest whole-number ratio of
the elements in the formula.
Molecular Formula: A chemical formula that gives the actual number of the elements in
the molecular compound.
Percent composition: The mass of each element in a compound compared to the
entire mass of the compound and multiplied by 100 percent.
○ Percent composition of an element in a compound =
n x molar mass of element
molar mass of compound
x 100%
n = the number of moles of the element in 1 mole of the compound
Mole ratio
Molar mass A
Molar mass A
Mole ratio
Mole ratio
Molar mass B
1.
56.25 g Kr=_____________________ mol Kr
2.
3.67 x 1023 atoms Ag =_________________ mol Ag
3.
243 L O2 = __________________ mol O2
4.
0.035 mol magnesium phosphate = _______________ g magnesium phosphate
5.
1.01 grams Fe= _________ atoms Fe
6.
2KCl + 3O2 → 2KClO3
How many grams of oxygen are necessary to react completely with 63.0 g of KCl in the
above reaction?
7.
2NH3 + H2SO4
(NH4)2SO4
How many kilograms of NH3 are needed to produce 1.00 ✕ 105 kg of (NH4)2SO4?
8.
MgO + CO2
MgCO3
6 CaO + P4O10
CaO + SO3
2 Ca3(PO4)2
CaSO4
(a) What mass of CO2 is needed to react with 124.6 g MgO?
(b) What mass of magnesium carbonate is produced?
(c) When 47.5 g P4O10 is reacted with an excess of calcium oxide, what mass of calcium phosphate is
produced?
9.
How many grams of sulfur (S) are needed to react completely with 519 g of Mercury
(Hg) to form HgS?
10.
How many moles of Fe are present in 39.4 g of the compound Fe2O3?
11.
C6H12O6
2 C2H5OH + 2 CO2
Starting with 500.4 g of glucose, what is the maximum amount of ethanol in liters that can be
obtained by this process? (Density of ethanol = 0.789 g/mL.)
12.
A compound is 64.9% carbon, 13.5% hydrogen, and 21.6% oxygen. Its molecular
mass is 74 g/mol. What is its empirical and molecular formula?
13.
How many liters of hydrogen must used to fully react 7.224x1024 atoms of carbon and create
octane?
14.
Tin (Sn) exists in Earth’s crust as SnO2. Calculate the percent composition by mass of Sn and I in
SnO2.
15.
There was an unknown compound with these percent compositions: 47.0% potassium, 14.5%
carbon, and 38.5% oxygen. What is the empirical formula? If the true molar mass of the compound is
166.22 g/mol, what is its molecular formula?
16.
If a manufacturer wanted to make 235 L of N2O, commonly known as laughing gas, how many
grams of nitrogen are needed if there is an excess of oxygen?
Answer Key
1.
0.6712 mol Kr
2.
0.610 mol Ag
3.
10.8 mol O2
4.
9.20 g magnesium phosphate
5.
1.08 x 10 22 atoms Fe
6.
24.7 g O2
7.
2.58 x 10 4 kg
8.
a)
b)
c)
9.
83.0 g
10.
0.493 mol
11.
0.324 L
12.
empirical: C4H10O
Molecular: C4H10O
13.
537.6 L
14.
Sn
O
15.
empirical: KCO2
molecular: K2C2O4
16.
231 g
136.1 g
260.7 g
104 g
78.77%
21.23%