Mole Notes
A __________ of a substance is 6.02 x 1023 representative particles of that substance.
Examples of representative particles:
The number of particles in a mole (6.02 x 1023) is called _________________________.
The mass of a mole of an element is its _________________________.
Molar mass is expressed in units of __________.
What are the molar masses of the following elements:
sodium:
oxygen:
silicon:
krypton:
The mass of a mole of a compound is called its _________________________.
The mass of a mole of BaSO4 is:
Find the formula mass of the following compounds:
Ca(NO3)2:
H2SO4:
CO2:
Ag3PO4:
At _________________________, one mole (6.02 x 1023 particles) of any gas occupies a
volume of 22.4L. This is also sometimes called the ___________________ of a gas.
STP =
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The Mole Road Map
Mass-Mole Calculations:
How many moles are in 57.2 g sodium metal?
What is the mass, in grams, of 1.43 mol of zinc metal?
How many moles are in 45.8 g of oxygen gas?
What is the mass, in grams, of 2.95 mol of bromine?
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Particle-Mole Calculations:
How many moles of magnesium is 1.25 x 1023 atoms of magnesium?
How many atoms are in 2.12 mol of propane (C3H8)?
How many moles is 2.17 x 1023 molecules of hydrogen gas?
How many atoms are in 1.14 mol SO3?
Volume-Mole Calculations:
What is the volume, in liters, of 0.60 mol SO2 gas at STP?
How many moles are in 7.50 L of C2H6 gas at STP?
What is the volume, in liters, of 3.70 mol N2 gas at STP?
How many moles are in 7.17 x 10-2 L of CO2 gas at STP?
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Mass-Particle/Volume-Particle Calculations:
How many atoms are in 183 g nickel metal?
What is the mass, in grams, of 7.25 x 1024 atoms of calcium?
How many liters are in 55.3 g chlorine gas?
What is the mass, in grams, of 1.50 x 1023 molecules of NH3?
How many liters are in 72.5 g nitrogen gas?
How many oxygen atoms are in 34.8 g calcium carbonate?
T.I._____
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Percent Composition
The relative amounts of the elements in a compound are expressed as the
_________________________ of each element in the compound.
% mass of element =
mass of element
mass of compound
× 100%
When a 13.60 g sample of a compound containing only magnesium and oxygen is
decomposed, 5.40 g of oxygen is obtained. What is the percent composition of this
compound?
A compound is formed when 9.03 g Mg combines completely with 3.48 g N. What is the
percent composition of this compound?
Propane (C3H8) is one of the compounds obtained from petroleum. Calculate the percent
composition of propane.
T.I._____
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Empirical Formulas
empirical formula:
Example: A compound is analyzed and found to contain 25.9% nitrogen and 74.1% oxygen.
What is the empirical formula of the compound?
Step 1: Assume 100 g of compound
Step 2: Convert grams into moles
Step 3: Divide all moles by the smallest number of moles
Step 4: If any moles are not whole numbers, multiply each mole by the smallest whole
number that converts all to whole numbers.
Step 5: Write the formula. The number of moles of each element becomes the subscript in
the compound.
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Calculate the empirical formula for each compound:
1. 94.1% O, 5.9% H
2. 67.6% Hg, 10.8% S, 21.6% O
3. 62.1% C, 13.8% H, 24.1% N
T.I._____
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Molecular Formulas
molecular formula:
Formula (name) Empirical or Molecular? Molar mass
CH
13
C2H2
2 × 13 = 26
C6H6
6 × 13 = 78
CH2O
30
C2H4O2
2 × 30 = 60
C6H12O6
6 × 30 = 180
To calculate the molecular formula from the empirical formula, divide the
_______________ by the _______________.
Example: Calculate the molecular formula of a compound whose molar mass is 60.0 g/mol
and the empirical formula is CH4N.
Example: Find the molecular formula of ethylene glycol. The molar mass is 62 g/mol and
the empirical formula is CH3O.
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Solve the following problems:
1. The compound methyl butanoate smells like apples. Its percent composition is 58.8%
C, 9.8% H, and 31.4% O and its molar mass is 102 g/mol. What is its empirical
formula? What is its molecular formula?
2. Muscle fatigue can result from the buildup of lactic acid resulting from overexercising. The percent composition of lactic acid is 40.0% C, 6.67% H, and 53.3% O.
What is the molecular formula of lactic acid if its molar mass is 90.0 g/mol?
3. Phenyl magnesium bromide is used in organic chemistry as a catalyst. Determine its
empirical and molecular formula if its molar mass is 181.3 g/mol and it contains
39.7% C, 2.78% H, 13.4% Mg, and 44.1% Br.
T.I._____
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