Chapter 11 – The Mole
11.1 Measuring Matter
 The mole
o The SI unit to measure the amount of substance
o 6.02 x 1023 representative particles
o Avogadro’s number
 Mole units
o Atoms
o Formula units
o Molecules
 Converting moles to particles
o Conversion factor:
Ex] How many molecules of sucrose are in 3.50mol of
sucrose?
Ex] How many formula units of NaCl are in 10.71mol of
NaCl?
 Converting particles to moles
o # of rep part x
_____1mol________ = # of moles
6.02 x 1023 rep part
Ex] Calculate the number of moles that contain 4.50 x 1024
atoms of zinc.
Ex] Calculate the number of moles that contain 8.73 x 1025
molecules of H2O.
11.2 Mass and the Mole
 Molar mass of an element
o Equivalent to atomic mass
o Unit is g/mol
o Molar mass of C =
o Molar mass of Ra =
 Converting moles to mass
Ex] Calculate the mass in grams of 0.045 moles of chromium.
Step 1 – Determine molar mass of Cr.
Step 2 – Use molar mass to convert known number of
moles to grams.
Ex] Calculate the mass in grams of 0.197 moles of silicon.
 Converting mass to moles
Ex] How many moles of calcium are in 525g Ca?
Step 1 – Determine molar mass.
Step 2 – Use molar mass to convert known mass to
number of moles.
 Converting mass to atoms
Ex] How many atoms of gold are in a nugget of gold with a
mass of 25.0g?
Step 1 – Determine molar mass.
Step 2 – Use molar mass to convert known mass to moles
of Au.
Step 3 – Use Avogadro’s number to convert known
number of moles to atoms of Au.
Ex] How many atoms of silver are in a nugget of silver with a
mass of 1.23g?
 Converting atoms to mass
Ex] A party balloon contains 5.50 x 1022 atoms of helium gas.
What is the mass in grams of the helium?
Step 1 – Use Avogadro’s number to convert known
number of atoms to moles.
Step 2 – Determine molar mass.
Step 3 – Use molar mass to convert known number of
moles to grams.
11.3 Moles of Compounds
 Chemical formulas and the mole
- Must look at formula and ratio of each element in the
formula.
Ex] CCl2F2, How many moles of F are in 2.5mol CCl2F2?
 Molar mass of compounds
- Number of moles x molar mass = number of grams
Ex] What is the molar mass of K2CrO4?
 Converting moles of compounds to mass
Ex] What is the mass if 2.50mol (C3H5)2S?
Step 1 – Calculate molar mass of the compound.
Step 2 – Use molar mass to change known number of
moles to mass.
Ex] What is the mass of 7.91mol Na2CO3?
 Converting mass of compounds to moles
Ex] How many moles of Ca(OH)2 are in 325g?
Step 1 – Determine molar mass of the compound.
Step 2 – Use molar mass to convert the known mass to
number of moles.
Ex] How many moles of KCN are in 114g?
 Converting the mass of a compound to number of particles
o Remember, there is no direct conversion from mass to
particles, you must first go to moles.
Ex] A sample of AlCl3 has a mass of 35.6g. How many Al3+
are present? How many Cl- are present? What is the
mass of one formula unit of AlCl3 (g/formula unit)?
Step 1 – Find molar mass.
Step 2 – Use molar mass to convert known mass into number
of moles.
Step 3 – Use known number of moles and Avogadro’s
number to convert to number of formula units.
Step 4 – To find number of ions, use ratios from the formula.
Step 5 – Mass of one formula unit =
Molar mass x inverse of Avogadro’s number
Ex] A sample of Na3PO4 has a mass of 17.4g. How many Na+
are present. How many PO43- are present? What is the
mass of one formula unit of Na3PO4?
11.4 Empirical & Molecular Formulas
 Percent composition of a compound
Ex] Determine percent by mass of each element in NaHCO3.
Step 1 – Calculate molar mass
Step 2 – Determine % by mass of each element by
dividing the mass of each element by molar
mass.
Ex] Determine percent by mass of each element in Fe2O3.
 Empirical formulas
o A formula with the smallest whole number mole ratio of
the elements.
o Hydrogen peroxide: Empirical formula HO
Molecular formula H2O2
Ex] Methyl acetate: 4806% C, 8.16% H, 43.20% O
Step 1 – Convert % to mass.
Step 2 – Divide each element’s mass by its molar mass to
get mole values.
Step 3 – Takes moles from step #2 and divide each by the
smallest number of moles calculated.
Step 4 – Multiply moles to get whole numbers.
Step 5 – Apply whole numbers to the elements provided
for the compound.
 Molecular formulas
o The formula that specifies the actual number of atoms of
each element in one molecule of a substance.
Ex] Succinic acid: 40.68% C, 5.08% H, 54.24% O
Molar mass = 118.1 g/mol
Step 1 – Convert % to mass and them convert grams to
moles using each element’s molar mass.
Step 2 – Determine mole ratio by dividing the smallest mole
value from #1 into each of the mole values
calculated.
Step 3 – Calculate the simplest mole ratio, multiply to get
whole numbers if necessary.
Step 4 – Use ratio from #3 to determine empirical formula.
Step 5 – Calculate empirical molar mass using the formula
created in step 4.
Step 6 – Divide the molar given in the problem by the
empirical molar mass calculated in step 5. This
answer will provide you with the number needed to
multiply the empirical formula by to get the
molecular formula.