Chemical Quantities
Avogadro’s Number
Many words are used to express
a specific quantity.
–Pair =2
–Dozen = 12
How do we measure matter?
• By mass – 1lb of bananas
• By volume – a gallon of milk
• By count – 20 calculators
How do we measure matter?
What if I wanted to know
how many ATOMS were
in this copper penny?
Would you like to count?
Could you?
• A mole is the most
appropriate unit when
dealing with atoms.
•
Avogadro’s Number
• You can count particles if you introduce a term
that represents a specified number of particles.
• 1 mole = 6.02 x 1023 (Avogadro’s number)
representative particles.
• Or 602,000,000,000,000,000,000,000
• A very large number!
MOLE
• A mole is the SI unit that measures the
amount of a substance.
• A mole can be related to:
• The number of particles
• The mass
• The volume of elements and
compounds

1 mole of hockey pucks would equal the mass of
the moon!

1 mole of basketballs would fill a bag the size of
the earth!

1 mole of pennies would cover the Earth 1/4 mile
deep!
MOLE
• Use dimensional analysis to
convert:
– moles to molecules
– moles to atoms
– moles to formula units
• Conversion Factor to Remember:
– 1 mol = 6.02 x 1023
• The units for Avogadro’s number
will be atoms, molecules, or
formula units.
• The unit depends on the type of
compound or if just a singular
element.
MOLE Examples
• How many moles are in 3.25 X 1020 atoms of
lead?
• How many moles are there in 8.3 x 1026
molecules?
• How many atoms are in 0.425 mol nitrogen?
• How many formula units are in 8.56 X 10-3 mol
NaCl?
Chemical Quantities
Molar Mass
Molar Mass
• Molar Mass equals 1 mole of an element or compound.
• To calculate Molar Mass:
1. Obtain all of the masses of the involved elements
from the periodic table.
2. Round mass to 2 decimal places.
3. Multiply each element’s mass by the subscript.
4. Add these masses
5. Round the answer to the proper number of
significant digits.
Terms to Know for
Mass of a Compound
• Molecular mass - mass of one
molecule of a covalent compound
(unit = amu)
• Formula mass - mass of one
formula unit of an ionic compound
(unit = amu)
• Molar mass - mass of one mole of
anything: molecules, formula units,
atoms, etc. (unit = g/mol).
Difference between
Molecular Mass & Molar Mass
• Same numerical value, but different units
Molar Mass of Element Examples
• Carbon = 12.01 g/mol
• Aluminum = 26.98 g/mol
VIDEO to more Discussion on the MOLE
The Mole and Avogadro's Number from Khan
Academy
Molar Mass of Compounds Examples
• Water
H2O = 2 hydrogen & 1 oxygen
2(1.01) + 16.00 = 18.02 g/mol
• Sucrose
C12H22O11 = 12 carbon, 22 hydrogen, 11 oxygen
12(12.01) + 22(1.01) + 11(16.00) = 342.34 g/mol
Molar Mass of Compounds
Examples
Sodium Chloride
– Find the formula
– How many of each
NaCl
1 sodium, 1 chlorine
– Multiply masses by subscripts and add the masses
1(22.99) + 1(35.45) = 58.44 g/mol
• Use dimensional analysis to
convert
– moles to mass or mass to
moles.
• Mass unit = grams
• Conversion Factor to Remember:
– 1 mol = molar mass of the element
or compound
Moles to Mass Examples
• How many moles of carbon are in 26 g of
carbon?
• How many grams are there in 2.37 moles of
CO2?
Moles to Mass Examples
• How many moles are present in 142.1
grams of NaCl?
• How many grams are in 3.34 moles of
potassium bromide?
Mole Calculations Learned
MASS
IN
MOLES
GRAMS
NUMBER
OF
PARTICLES/
ATOMS
LITERS
GAS
Chemical Quantities
Percent Composition
Percent Composition
• Percent composition is the percent of that
element in the compound….the total percent for
the compound will equal 100%.
• Formula for Percent Composition:
mass of element
% compositio n 
 100
total mass
Percent Composition Examples
• Example: 9.03 g Mg combined completely with
3.48 g N to form a compound.
• What is the percent composition of the
compound?
– 9.03g + 3.48g = 12.51 g (total mass)
– 9.03/12.51 x 100 = 72.2 % of Mg
– 3.48g/12.51 x 100 = 27.8% of N
• Check: Add % Composition of each element to see if adds up to 100%
– 72.2 % of Mg + 27.8% of N = 100%
Percent Composition Examples
• When the mass of each element is not given,
calculate the molar mass of each element in the
compound before calculating the % composition.
• Example: Calculate the percent composition of C2H6.
– Mass of 1 mol of Carbon = 12.0g x 2 = 24g
– Mass of 1 mol of Hydrogen = 1.0g x 6 = 6g
– 24g/30g x 100 = 80%
– 6g/30g x 100 = 20 %
• Be sure to check your work.
More Percent Composition
Examples
• Calculate the % Composition of these
compounds:
– NaHSO4
– NH4Cl
Chemical Quantities
Empirical Formulas
Empirical Formulas
• The empirical formula gives the lowest whole
number ratio of the elements in a compound.
– Reduces the subscripts.
• The empirical is sometimes and sometimes not
the same as the molecular or “actual” formula.
– For ionic compounds, the formula unit is the empirical
formula.
• Example when NOT:
– The empirical formula for H2O2 is HO.
Empirical Formulas
• The molecular formula for vitamin C is
C6H8O6. What is the empirical formula?
–A. CHO
–B. C3H4O3
–C. CH2O
–D. C2H4O2
Empirical Formulas
• Which of the following is an empirical
formula?
–A. C3H6
–B. NaCl
–C. CH4
–D. C4H10
VIDEO to more Discussion on the MOLE
Emp and Mol formulas from Percent
composition