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Which compound in the following list is NOT possible?
1. CaBr2
50%
2. KI
3. Al2O
4. LiCl
17%
5. MgO
17%
9%
1
2
7%
3
4
5
Which compound is NOT ionic?
(Which one is a molecular compound?)
LiCl, lithium chloride
2. SO2, sulfur dioxide
3. AlF3, aluminum fluoride
4. Ba(NO3)2, barium nitrate
5. NaHCO3, sodium hydrogen
carbonate
1.
38%
17%
15%
18%
12%
1
2
3
4
5
Which compound formula name is NOT correct?
CaSO4, calcium sulfate
2. NaNO3, sodium nitrate
3. MgI2, magnesium iodide
4. NH4PO4, ammonium phosphate
5. Ca(ClO)2, calcium hypochlorite
1.
46%
22%
12%
1
10%
2
10%
3
4
5
Sodium oxalate has the formula Na2C2O4. Based on this
information, what is the formula for iron (III) oxalate?
1. FeC2O4
41%
37%
2. Fe(C2O4)2
3. Fe(C2O4)3
4. Fe2(C2O4)3
17%
5. Fe3(C2O4)2
5%
0%
1
2
3
4
5
Chapter 3- Stoichiometry
 Stoichiometry=
 Compound stoichiometry


quantitative (mass) relationships among elements in compounds
Reaction stoichiometry

the quantitative relationships among substances as they
participate in chemical reactions
The Mole
 Connects macroscopic to atomic world
 Atoms are really small- a measurable quantity of




matter contains A LOT of atoms
1 dozen = 12 objects
1 mole = 6.022 x 1023 objects
6.022 x 1023 is called Avogadro’s number
Unit sign: mole=mol
Why is the mole a convenient unit for us to use?
 The mass of 1 mol of an element is equal to its atomic
mass in grams
 Molar mass is in g/mol
 Molar mass of lithium= 6.939 g/mol
How do we use it?
 Conversion factors
 Avogadro’s number
23
1
mol
6
.
022
x
10
particles
23
1
mol

6
.
022
x
10
particles
23
6
.022
x
10
parti
1
mol

Molar Mass
gLi
1
mol

6.939
g
Li 6.939
1mol
1mol
6.939
gLi
Examples
1. How many atoms are in 0.7 mol of Ar?
2 . H o w m a n y m o l e s d o 3 . 0 0 x 1 0 20 a t o m s o f B
make?
3. How many moles do 41.0g of C make?
4. How many moles do 41.0g of He make?
5. What is the mass of 1 platinum (Pt) atom?
What is the mass of 2.60 mol of O?
1. 8.90 g
84%
2. 0.163 g
3. 2.60 g
4. 41.6 g
5%
1
7%
2
5%
3
4
Example
How many C atoms are in a 0.96-carat
diamond? (1 carat=0.2g)
Compounds and Moles
 1 mole of a compound contains 6.022 x 1023
molecules or “units”
 Molar mass = sum of atomic molar masses



H2O
CO2
Fe(NO3)3
Example
Consider UF6
•
•
•
•
•
What is the molar mass?
How many grams in 0.5 mol?
How many molecules in 0.5 mol?
How many U atoms in 0.5 mol?
How many F atoms in 0.5 mol?
Molecular vs. Nonmolecular compound terms
 1 mol CO2 contains 6.022 x 1023 molecules
 1 mol NaCl contains 6.022 x 1023 formula units
Percent Composition
 The fraction of mass due to an element




mass
of
eleme
#
atom
of
elem
in
for
ma
of
el
Percent
compos
n

x
100
%

x
1
%
total
mass
mas
of
com
Determining Formulas from % Composition
 The ratio of atoms in the formula is the same as the
ratio of moles of those elements.
 If you determine the ratio of moles, you know the
formula.
 However, the formula determined is the empirical
formula.
Examples
1 . W h a t i s t h e % c o m p o s i t i o n o f H i n H 2O 2?
2. Which of the following has the highest %
composition of copper, Cu? (Don’t use a
calculator)
CuSO4
Cu2SO4
CuCO3
Cu2CO3
3. A compound has Ca, S, and O. What is the
empirical formula?
Ca:
29.45%
S:
23.55%
O:
47.00%
Empirical vs. Molecular Formulas
Example: Ethene is C2H4
Percent composition tells us mol H/mol C = 2
The empirical formula is CH2.
The molecular formula is C2H4.
Example:
A hydrocarbon has 82.65% C and 17.34% H
Molar mass is 58.12 g/mol
What are the empirical and molecular formulas?
Hydrated Compounds
Solids in which molecules of water are trapped and
become part of the compound.
Ex: Gypsum: CaSO4 • 2H2O
is hydrated calcium sulfate
CaSO4 is anhydrous calcium sulfate
Determining the number of waters of hydration
1.023 g CuSO4 • x H2O is heated to drive off the
water. The resulting anhydrous CuSO4 has a mass
of 0.654 g. What is the value of x?