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Chapter 10
The Mole
10.1 Measuring Matter
• Dozen eggs
• Pair of gloves
The mole
• SI unit, measures the amount of substance
• 602,213,670,000,000,000,000,000
– A mole of pennies would be
$6,022,136,700,000,000,000,000
– six sextillion, twenty-two quintillion, one hundred
thirty-six quadrillion, seven hundred trillion dollars
• 6.02 x 1023 particles of matter
• 6.02 x 1023 = Avogadro’s number
– The number of representative particles in one
mole of a pure substance
– Representative particle =
• Formula unit (ionic compounds)
• Molecule (covalent compounds)
• Atom
ONE MOLE OF
• Fe = 6.02 x 1023 atoms
• H2O = 6.02 x 1023 molecules
• CaCl2 = 6.02 x 1023 formula units
MOLES
REPRESENTATIVE
PARTICLES
• Conversion factor =
– 6.02 x 1023 particles
1 mole
How many atoms are in 2.00 mol of argon?
• How many molecules are in 7.25 mol of
carbon dioxide?
• Challenge: How many oxygen atoms are
in 5.0 moles of oxygen molecules?
(Oxygen is diatomic)
REPRESENTATIVE PARTICLES
MOLES
• How many moles are in 1.62 x 1023 atoms
of argon?
• How many moles are in 4.35 x 1024
molecules of dinitrogen triflouride?
10.2 Mass and the Mole
• Molar mass = the mass in grams of one
mole of a pure substance (atom, molecule,
formula unit)
– Equal to atomic mass (on periodic table)
– Unit = g/mol
• Mass of atoms is found on the periodic
table
–K=
• Mass of compounds must be calculated
– H20
– CO2
Calculating molar mass
• What is the molar mass of barium
acetate?
• What is the molar mass of ammonium
sulfate?
MASS
MOLES
• How many moles are in 12.5 g of Carbon
dioxide?
• How many moles are in 83.2 g of H2SO4?
MOLES
MASS
• What is the mass in grams of 1.5 mol of
sodium chloride?
• What is the mass in grams of 0.774 mol of
oxygen?
CONVERTING BETWEEN UNITS
• Must ALWAYS go to moles first
Particles
Mass
Volume
Moles
Volume
Mass
Particles
• How many atoms are in a 44.3 g piece of
iron?
• What is the mass in grams of 2.3 x 1022
formula units of sodium phosphate?
• How many aluminum ions are present in
35.6 g AlCl3?
• How many chlorine ions are present in
35.6 g AlCl3?
10.4 Empirical and Molecular
Formulas
• Empirical formula – shows the smallest
whole-number ration of atoms in a
compound
• Molecular formula – gives the actual
number of each kind of atom in a molecule
• C6H12O6
Percent Composition
• The percent by mass of each element in a
compound
• The percents of all the elements should
add up to 100
Calculating % Composition
1. Find the total molar mass of each
element in the compound.
2. Find the molar mass of the entire
compound.
3. Divide the total molar mass of each
element by the molar mass of the
compound then multiply by 100
4. Check that all your percentages add up
to 100
% composition of C3F6
1. Total mass of C =
total mass of F =
2. Mass of compound C3F6 =
3. % of C =
4. Check your work!
% of F =
• What is the percent composition of
phosphoric acid?
Empirical Formula
• The formula with the smallest whole
number ratio of elements in a compound
Calculating Empirical Formulas
1. Change % to g (assume 100 g of
compound so 30% = 30 g)
2. Convert each element from g to moles
3. Divide each mole amount by the smallest
number from step 2
4. Change to a whole number = subscript in
empirical formula
• What is the empirical formula for a
compound that is 48.64% Carbon, 8.16%
Hydrogen, and 43.20% Oxygen?
• What is the empirical formula of a
compound that is 43.7% P and 56.3% O?
Molecular Formula
• To find the molecular formula you must
know
– Empirical formula
– Molar mass of compound
• Can be the same as the empirical formula
but often is not
Calculating Molecular Formula
1. Calculate the mass of the empirical
formula
2. Divide molar mass of compound (will be
given) by mass of empirical formula
3. Multiply each subscript in the empirical
formula by the answer from step 2
• A compound who’s empirical formula is
NO2 has a molar mass of 92 g/mol. What
is the compound’s molecular formula?
• An unknown compound contains 58.5%
carbon, 9.8% hydrogen, and 31.4%
oxygen. Its molar mass is 102 g/mol. What
are its empirical and molecular formulas?