Joe Pecoraro
Rebecca Pasch
Moles/Stoichiometry Note and Review Sheet
Basic Rules/ Guidelines
 The mole is a unit of measurement used by chemists to convert from different
units, such as mass, volume, particles, and more.
 The mole is the SI unit for the amount of substance.
 Just like the factor label method, it is helpful to include the units in each step of
the problem in order to determine whether to multiply or divide by each unit.
 Ultimately, all of you units will cancel, and the answer will be in the unit that is
specified in the problem.
Particles
 The mole was discovered by Amedeo Avogadro. He also invented to Avogadro’s
number 6.02X1023 over 1 mole, which is the number of particles, atoms or
formula units in one mole depending on the type of compound.
 Avogadro’s number I used from converting from moles to particles, which can
consist of formula units, and atoms.
 Use Avogadro’s number when converting only between particles and moles,
because al other conversions must go directly through moles.
 Careful, when using a calculator, use E instead of X 1023, because it will yield the
incorrect answer otherwise.
Volume
 Volume is measured in liters or milliliters.
 To convert from or to volume, you must be in moles first because it is the only
unit of measure that can directly convert into volume.
 The number used to convert volume to moles or moles to volume is 22.4 Liters
over 1 mole, which can be multiplied or divided depending on how the units
would cancel.
 Because 22.4 liters is the conversion factor used in converting, if given milliliters,
convert it to liters first, and then solve.

If given a specific density in the problem, use that to convert form moles to
volume instead of 22.4 Liters.
Mass
 Mass is measured in grams.
 To convert between moles and grams, the previously calculated molar mass over
1 mole must be used.
 Molar Mass- is the total grams of all elements in the compound.
 Molar mass is the sum of the atomic masses of each respective elements.
 For example, the molar mass of H2O would be 18.02 because Oxygen has a mass
of 16.0 grams, and each Hydrogen has a mass of 1.01. Therefore, adding them all
yields 18.02 grams for the molar mass.
 When converting, the molar mass will always cancel out with the given mass.
Mole Ratio
 Based on the balanced chemical equation in the problem, the coefficients of the
different elements or compounds are sued when converting between different
elements.
 The mole ratio is used in slightly more complex problems when having to switch
the actual compounds being measured.
 For example, given mass of Hydrogen, you would have to the molar mass and the
mole ratio to convert to grams of oxygen.
Empirical/Molecular Formula
 Besides just converting, moles can be used to determine the empirical and
molecular formulas of a problem.
 Empirical formula- the simplified formula of a compound. Ex. CH2O
 Molecular Formula- When the ratio of the number of each elements in each
compound is not reduced. Ex. C6H12O6
 Steps to find Empirical Formula:
1. Assume 100 grams
2. Convert to moles
3. Divide by the smallest
4. Multiply until whole.
 Use ratio of molar mass to mass of compound given to find the molecular formula
of compound.
Finding Percent Composition
 Percent Composition- amount of compound that is made up by each respective
element.
 To find:
1.
2.
3.
4.
Find molar mass of compound.
Find total molar mass for each element.
Divide molar mass of each element by molar mass of compound.
Multiply by 100.
**To convert to or from volume, grams, or particles, moles must
be used as a unit of conversion and act as a stepping stone between
units.**
Review Problems
1. N2(g) + 3H2(g) yields 2NH3(g)
How many grams of Hydrogen are there if there are 75 grams of Nitrogen?
2. 2H2(g) + O2(g) yields 2H2O(l)
If you have 12 Liters of Hydrogen, how many liters of Oxygen are there?
3. MgCl2(aq) Yields 1 Mg(s) + 1 Cl2(g)
How many grams of Chlorine if you have 9 Liters of Mg?
4. 2AgNO3 + SrCl2 Yields 2AgCl + Sr(NO3)2
If there are 50,0 grams of AgNo3, how many moles of AgCl are there?
5.Find the Empirical and molecular formulas if you have 73.13% Carbon, 7.38%
Hydrogen, and 19.49% Oxygen. The molecular mass of the compound is 246.33 g/mol.
6. 2 CO(s) + O2(g) Yields 2 CO2(g)
How many liters of CO2 form from 7.82 particles of O2?
7. Calculate the percent composition of AgCl.
8. Calculate the percent composition of KNO3.
9. Calculate the number of C, H, and O atoms in 7.50 grams of C6H12O6.
10. AgNO3(aq) + KCL(aq) Yields AgCl(aq) + KNO33(aq)
How many Kg of KCl are needed to produce 1.00 X 105 Kg of AgCl?
11. 2 Ca(s) + O2(g) Yields CaO(s)
What is the minimum amount of Ca in moles needed to have 7.35 grams of O2?