Download Chapter 6 Stoker-Calculations

Chapter 6
Chemical Calculations: Formula Masses, Moles, &
Chemical Equations
Atomic Mass = the weighted average of masses of all naturally-occurring
isotopes of an element
Formula Mass = the sum of the atomic masses of all the atoms represented
in the chemical formula
Calculate the Formula Mass:
SnF2
Al(OH)3
The Mole
A chemistry counting unit!
1 Mole of an element = the atomic mass in grams
How much is a mole?
1 mole of Al
1 mole of H2O
1 mole of NaCl
#/type of particles
molar mass
1 Mole of any element contains the same number of atoms as
1 mole of any other element
1 Mole of a molecular compound contains the same number of molecules
as 1 mole of any other molecular compound
1 Mole of an ionic compound contains the same number of formula units
as 1 mole of any other ionic compound
Particles
Moles
Grams
The Mole = a Chemistry Counting Unit
1. Find the number of atoms in 3.00 moles of copper:
3.00 mole Cu x 6.02 x 1023 atoms =
mole Cu
2.
Find the number of molecules in 0.485 mole of CO2.
3.
How many moles of water contain 7.50 x 1025 molecules?
4. How many moles of silicon are represented by
1.55 x 1020 atoms of silicon?
What does a mole look like?
Copper
Cu
Carbon
C
Water
H2O
Sugar
C6H12O6
Salt
NaCl
Calculating Molar Mass of a Compound
H2O
C2H6O
(NH4)2Cl
Converting Mass to Moles (element)
mass (g) x
1 mole
= moles
molar mass (g)
Example: How many moles of copper are in 5.00 grams of copper?
Converting Moles to Mass
moles x molar mass (g) = mass (g)
1 mole
Example: How many grams of copper are equal to 6.25 mole of copper?
Converting Mass to Moles (compound)
mass (g) x
1 mole
= moles
molar mass (g)
Example: A box of salt contains 737 grams of NaCl. How many moles of
NaCl are present?
Converting Moles to Mass
moles x molar mass (g) = mass (g)
1 mole
Example: How many grams of ethanol (C2H6O) are equivalent to
2.6 x 103 moles of ethanol?
Converting Mass to Atoms
mass (g) x
1 mole
x
molar mass (g)
6.02 x 1023 atoms = # of atoms
1 mole
Example: How many atoms of copper are in 25.0 grams of copper?
Example: Find the number of gold atoms in a ring that contains 12.8 grams
of gold.
Moles of Elements in a Formula
Subscripts in a chemical formula indicate the number of atoms
of each type of element in a molecule:
Writing and Balancing Chemical Equations
1.
Write an equation using the correct formulas of reactants & products.
CH4(g) + O2(g)
CO2(g) + H2O(l)
2.
The State may be specified
solid
(s)
liquid
(l)
gas
(g)
aqueous (aq)
3.
Conditions may be written above or below the arrow

heat
catalyst Pt
Writing and Balancing Chemical Equations
1.
Use Coefficients (in front of formula) to balance
2.
Hints:
3.
start with the element that has the largest number of atoms
do H & O next
save free elements for last
treat polyatomic ions as single entities (if they do not change)
Don’t change any subscripts!
CH4(g) + O2(g)
Count atoms of each element:
C
H
O
Use coefficients to balance each element:
CO2(g) + H2O(l)
Writing and Balancing Chemical Equations
Al(s) + Cl2(g)
AlCl3(s)
C3H8(g) + O2(g)
CO2(g) + H2O(l)
Writing and Balancing Chemical Equations
Mg(s) + HCl(aq)
MgCl2(aq) + H2(g)
Fe(s) + O2(g)
Fe2O3(s)
Balancing Equations with Polyatomic Ions:
Na2SO4(aq) + BaCl2(aq)
Count ions on each side:
NaCl(aq) + BaSO4(s)
Balancing Equations with Polyatomic Ions:
Na3PO4(aq) + MgCl2(aq)
NaCl(aq) + Mg3(PO4)2(s)
NaOH(aq) + H2SO4(aq)
Na2SO4(aq) + H2O(l)
Recognizing Reactions by Pattern (Chapter 9.1):
Combination Reactions
Decomposition Reactions
Single Replacement Reactions (Displacement)
Double Replacement Reactions (Exchange)
Exchange of Cations & Anions (Double Replacement Rxn)
1.
Formation of an insoluble product = precipitation
AgNO3(aq) + NaCl(aq)
2.
AgCl(s) + NaNO3(aq)
Formation of a molecular liquid (like water) = neutralization
HCl(aq) + NaOH(aq)
NaCl(aq) + H2O(l)
3. Evolution of a gas
HCl(aq) + NaHCO3(aq)
NaCl(aq) + H2CO3(aq)
H2O(l) + CO2(g)
Classify as Decomposition, Combination, Single Replacement or
Double Replacement; Name all compounds/elements:
1. Na2S + CuCl2
2 NaCl + CuS
2. Ca + Cl2
CaCl2
3. CaCO3
CaO + CO2
4. Zn + CuCl2
ZnCl2 + Cu
Balance & Classify as Decomposition, Combination, Single Replacement or
Double Replacement
1. Ca + O2
CaO
2. KClO3
KCl + O2
3. ZnCl2 + AgNO3
Zn(NO3)2 + AgCl
4. Zn + HCl
ZnCl2 + H2
5. Fe + O2
Fe2O3
6. BaCl2 + K2SO4
BaSO4 + KCl
Balance & Classify as Decomposition, Combination, Single Replacement or
Double Replacement
1. CaCl2 + Na2CO3
2. Fe2S3
3. Ca + Cl2
CaCO3 + NaCl
Fe +
S
CaCl2
4. Cu + AgNO3
Cu(NO3)2 + Ag
5. PbO + HNO3
Pb(NO3)2 + H2O
We can also classify chemical reactions by Reaction Type
Combustion Reactions – give off heat & light
CH4(g) + 2 O2 (g)
CO2(g) + 2 H2O(g)
Combustion Reactions
Reaction of a carbon-containing compound with oxygen to generate heat and light
Combustion of a hydrocarbon gives carbon dioxide & water:
2 C2H6(g) + 7 O2(g)
4 CO2(g) + 6 H2O(g)
Combustion of a carbohydrate gives carbon dioxide & water:
C6H12O6(s) + 6 O2(g)
6 CO2(g) + 6 H2O(g)
Classification by Reaction Type
Acid-Base Reactions (Neutralization) – give a salt & water
H2SO4(aq) +
KOH(aq)
Precipitation Reactions – an insoluble compound is produced
ZnCl2(aq) + AgNO3(aq)
Oxidation-Reduction Reactions – involve an exchange of electrons
Zn(s) + CuSO4(aq)
Mole Relationships in Chemical Equations
Conservation of Mass: in any chemical reaction, the total mass of the reactants
is equal to the total mass of the products.
2Ag (s) + S(s)
Atoms:
Moles:
Mass:
Total mass:
Ag2S(s)
Chemical Calculations Using Chemical Equations
28.60 grams of copper reacts with 7.22 grams of sulfur in a
combination reaction:
Cu + S
Mass:
28.60
Moles:
Molar Ratio:
What is the product?
7.22
?
35.82 grams
Empirical Formula of a Hydrate (lab)
5.00 g of CaCl2XH2O were heated.
3.78 g of the anhydrous salt remain.
a) Write a chemical equation for the decomposition of the hydrate.
CaCl2XH2O(s)
a) Find the Formula of the hydrate.