Chemical Quantities
Chapter 10:The Mole
Measuring Matter:
If one marble has a mass of 4.5g, how many
kilograms will 230 marbles have?
ans: 1.035 Kg
How many grass seeds are in a 40 kg bag of seeds if one
grass seed has a mass of 0.125g?
ans: 320 000 seeds
The Mole:
• An expression of the quantity of matter. The
quantity of matter is referred to a representative
particles.
• One mole = 6.023 x 1023 quantity (Avogadro’s #)
• The representative particles are:
1. Atoms: One mole of atoms = 6.023 x 1023
atoms.
2. Molecules: One mole of molecules =
6.023 x 1023 molecules.
3. Ions: One mole of ions = 6.02 x 1023 ions
4. Compounds: One mole of compound =
6.023 x 1023 compounds.
The Mole Concept
To find Molar Mass:
• Gram atomic mass (gam) is the mass of the atom
Reference off the periodic table.
Cl
Ni
Ba
Ag
N
To find Molar Mass:
Gram molecular mass (gmm) is the sum of mass of
atoms in a molecule.
CO2
C 2H8
NO2
Cl2
CCl4
N2
To find Molar Mass:
• Gram formula mass (gfm) is the sum of the mass of
atoms in an ioinc compound.
NaCl
Na2SO4
Fe2O3
Ba3(PO4)2
Determine the Molar Mass
Find the gam for Ca ______ and Pb ______
Find the gfm for K2CrO4
Find the gmm for N2O5
TLS: Complete Molar Mass Review
HW: #34-36 all page 335
The Mole Concept
Sampler
• Text page 323, Practice #1-4.
• Text page 324, Practice #5-6
• Text page 335, Problems #34-36
To determine:
The mass in moles of an atom:
• reference the periodic table.
• Note: 1 mole of Na atoms = 6.02 x 1023 Na atoms =
23g (the atomic mass of Na)
• *the atomic mass of any element is the molar mass
(in g/mol) of that element.
• The Mole Concept flowchart.
The Mole Concept
The mass to mole relationship.
Find the gfm, gmm, or gam for the given
compound
Convert given # if grams to moles of
compound using
1 mole = gfm, gmm or gam
1. How many moles in 2.5 g of NaCl?
2. How many moles of N2O5 are in 35 g of N2O5?
*the mole to mass relationship.
3. How many grams of CO2 gas are in 2.5 moles of
CO2 gas?
4. How many grams of chlorine gas are in 40 moles of
chlorine gas?
*The Mole to Mass and Mass to
Mole Relationship for Elements :
Text page 328-329, Practice #15#18
#15b
#17b
The # of molecules in a given # of
moles.
Write the # of moles given
Use the molecules to mole relationship.
1 mole of molecule = 6.02 x 1023 molecules.
1. How many molecules are in 2 moles of H2O?
2. How many moles of hydrogen are in 2 moles of
H2O?
• TLS: Practice #29-#36 pp335.
Apply the Mole Concept
Given mass converts to mole using (1 mole = gfm,
gmm,or gam)  Mole converts to molecule using (1
mole = 6.023 x 1023 ) Number of Molecules.
How many molecules of CO2 are there in 23 g of CO2?
Ans: 3.15 x 1023 molecules of CO2
HW: Problem Set Three
Textbook: page 331 #19-20 and page 339 #42-46
Percent Composition
refers to what part by mass of a compound does
each element contribute. NOTE page 342.
Formula: MolarMass of element X 100 = %
Molar Mass of compound
•
Sample
• Calcium Chloride : CaCl2
Ca: 1 x 40 = 40
Cl: 2 x 35 = 70
110 is the total mass
• % Comp Ca = 40 x 100 = 36.36 %
110
• % Comp Cl = 70 x 100 = 63.6 %
110
100 %
• TLS: Practice #54-57 pp 344.
Empirical Formula
Expression of the smallest whole
number ratio of elements in a
molecule.
1. May or may not be the same as the
molecular formula.
2. Total percentage of any compound
is 100%. The % = mass
a. Given 36.63% Ca will = 36.63 g Ca
Procedures: Empirical
Formula
1. Convert % to mass (total percentage is 100%).
2. Convert mass to moles via the gfm.
3. Divide the moles by the smallest mole value to
determine the mole ratio within the compound.
4. If not a whole number, multiply the mole ratio from
#3 by the smallest whole #.
5. The answers are the subscript in the empirical
formula.
Sampler #1
The % composition of an unknown compound is found
to be 38.43% Mn, 16.80% C and 44.77% O. What is
the empirical formula for this compound?
Sampler #2
Calculate the empirical formula for a compound
whose % composition is 74.97% Al and 25.03% C ?
Sampler #3
What is the empirical formula of compound
composed of 37.01 % Carbon, 2.22 % Hydrogen,
18.50 % Nitrogen, and 42.27% Oxygen?
HW: #58-61 page 346
Molecular Formula
Actual number of elements expressed in a molecule.
a. molecular formula = empirical formula x n
b. Formula:
molar mass of the molecule = MW = n
mass of the empirical formula EW
n = the number of moles
Sampler Molecular Formula
A compound has a molecular mass of 118 g/mol and is
composed of 40.68% carbon, 5.08% H and 54.24% O.
What is the molecular formula?
Page 350, #65
TLS: Practice #62-64 pp 350.
Hydrates
Compounds with water molecules attached.
a. Review the prefixes. (Table 10-1, pp 351)
b. The mass of the water is included in the
mass of the total molecule.
c. Calculation of % composition, empirical
formula and molecular formula is the same
with hydrate. EXCEPT the mass of the water
molecules are included.
TLS: Practice #74 and #75 p 353
Hydrated Sample
A hydrate of aluminum bromide is composed of
71.16% AlBr3 and 28.84% H2O. What is the
formula for this hydrate?
Hydrated Sampler #2
A 17.44 g sample of hydrated zinc (II) sulfate is heated
to drive off the water. After heating, 9.79 g of
anhydrous zinc(II) sulfate remain. Find the hydrated
formula.
Hydrated Sampler #3
What is the % composition of a hydrated Lead (II)
acetate if the molecule is composed of 14.25%
water by mass?
What is the hydrated formula?
Page 361; #184 and #185