5/8/2012
Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
The molar mass = the sum of all the atomic masses.
The molar mass = the sum of all the atomic masses.
Example Ca(NO3)2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams
Example Ca(NO3)2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams
You try one:
What is the gram formula mass (molar mass) of Mg 3(PO4)2?
You try one:
What is the gram formula mass (molar mass) of Mg3(PO4)2?
3(24.305) + 2(30.97376) + 8(15.9994) = 262.86 grams
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Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
The molar mass = the sum of all the atomic masses.
The molar mass = the sum of all the atomic masses.
Example Ca(NO3)2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams
Example Ca(NO3)2 = 40.08 + 2(14.01) + 6(16.00) = 164.10 grams
What is the gram formula mass (molar mass) of Mg 3(PO4)2?
What is the gram formula mass (molar mass) of Mg 3(PO4)2?
3(24.305) + 2(30.97376) + 8(15.9994) = 262.86 grams
3(24.305) + 2(30.97376) + 8(15.9994) = 262.86 grams
What is the percent Magnesium in Mg 3(PO4)2?
What is the percent Magnesium in Mg 3(PO4)2?
Answer: 3(24.305) x 100 = 27.7%
262.86
Answer: 3(24.305) x 100 = 27.7%
262.86
What is the percent Lithium in Li2SiO3?
molar mass = 2(6.941) + 28.0855 + 3(15.9994) = 89.9657 g
% Li = 2(6.941) x 100 = 15.4%
89.9657
What is the percent Lithium in Li2SiO3?
Chemistry SOL Review— Molar Relationships

A Brief Return to Empirical Formulas
Empirical Formulas are the reduced form of Molecular formulas.
For example: The empirical formula for C 5H10 is CH2.
A favorite SOL type question:
What is the empirical formula of a compound that contains 30% Nitrogen and
70% Oxygen?
a) N2O
b) NO2
c) N2O5
d) NO

This is really a percent
composition problem. Figure
out which compound contains
30% nitrogen.

Nitrogen gas is a diatomic molecule. What is the mass of
one mole of nitrogen gas?
A 7g
B 14 g
C 28 g
D 6 x 1023 g
How many grams of nitrogen are present in 2 moles of
HNO3?
A 1
B 2
C 14
D 28
What is the mass in grams of one mole of sulfur dioxide
(SO2)?
A 48.1 g
B 64.1 g
C 80.1 g
D 96.1 g
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


What is the molar mass of Al(NO3)3?
A 57 g/mol
B 103 g/mol
C 165 g/mol
D 213 g/mol
What is the percentage of aluminum in aluminum oxide
(Al2O3)?
A 47%
B 48%
C 53%
D 54%
A compound is composed of 85.64% carbon and
14.36% hydrogen. The compound has a formula mass of
42.08 grams. What is the molecular formula?
A CH2
B C3H6
C C2H4
D C2H18
Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
At Standard Temperature and Pressure (STP) 1 mole of gas = 22.4 L
You can use this to calculate the density of a gas in g/Liter at STP.
Example: What is the density of CO2 gas at STP?
The molar mass of CO2 = 12.0111 + 2(15.9994) = 44.0099 g
Density = mass/volume = 44.0099 g/22.4 L = 1.96 g/L
Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
At Standard Temperature and Pressure (STP) 1 mole of gas = 22.4 L
At Standard Temperature and Pressure (STP) 1 mole of gas = 22.4 L
You can use this to calculate the density of a gas in g/Liter at STP.
You can use this to calculate the density of a gas in g/Liter at STP.
Example: What is the density of CO2 gas at STP?
Example: What is the density of CO2 gas at STP?
The molar mass of CO2 = 12.0111 + 2(15.9994) = 44.0099 g
The molar mass of CO2 = 12.0111 + 2(15.9994) = 44.0099 g
Density = mass/volume = 44.0099 g/22.4 L = 1.96 g/L
Density = mass/volume = 44.0099 g/22.4 L = 1.96 g/L
What is the density of Cl2 gas at STP?
What is the density of Cl2 gas at STP?
Answer: molar mass = 2(35.453) = 70.906 g
70.906 g/22.4 L = 3.165 g/L

What is the density of carbon dioxide at
STP?
A 1.96 g/L
B 22.0 g/L
C 46.0 g/L
D 5.09 x 10-1 g/L
Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
One mole = 6.02 x 1023 representative particles
One mole = 22.4 Liters of gas at 0°C and one atmosphere
of pressure
One mole = the atomic mass listed on the periodic table.
For example: one mole of Helium contains 6.02 x 1023
atoms of Helium and it has a mass of 4.00260 grams. At
0°C and one atmosphere of pressure, it would occupy
22.4 Liters.
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Given
X
1
Unknown
Unknown
Known
Given
How many liters would 2.0 moles of Neon
occupy?
Sample problem: How many moles are in 15.2 grams of
Lithium?
Sample problem: How many liters would 2.0 moles of Neon
occupy?
Answer:
15.2 g Li x 1 mole Li = 2.19 mole Li
6.941 g Li
Answer:
2.0 moles Ne x 22.4 Liters Ne = 44.8 Liters Ne
1.0 moles Ne
Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
Chemistry SOL Review— Molar Relationships
The Mole and Mole Calculations
One mole = 6.02 x 1023 representative particles
One mole = 6.02 x 1023 representative particles
One mole = 22.4 Liters of gas at 0°C and one atmosphere of
pressure
One mole = 22.4 Liters of gas at 0°C and one atmosphere of
pressure
One mole = the atomic mass listed on the periodic table.
One mole = the atomic mass listed on the periodic table.
Sample problem: How many liters would 14 grams of Helium
occupy?
You try one:
Answer:
14 g He x
What is the mass of 9.0 Liters of Argon gas at 0°C and one atmosphere of
pressure?
22.4 L He = 78 Liters He
4.0026 g He
Chemistry SOL Review— Molar Relationships

The Mole and Mole Calculations
One mole = 6.02 x 1023 representative particles
One mole = 22.4 Liters of gas at 0°C and one atmosphere
of pressure

One mole = the atomic mass listed on the periodic table.
What is the mass of 9.0 Liters of Argon gas at 0°C and one
atmosphere of pressure?
9.0 L Ar x 39.948 g Ar = 16 g Ar
22.4 L Ar


Which volume will be occupied by a gas containing 6.02 x 1023 atoms at
STP?
A
1.0 L
B
11.2 L
C
22.4 L
D 44.8 L
Which of these is about 2 moles?
A
2.0 liters (dm3) of H2
B
4.0 grams of H2
C
2.0 x 1023 molecules of H2
D 4.0 kilograms of H2
The gas with the largest volume at STP is —
A
10.0 g He
B
10.0 g Ne
C
10.0 g Ar
D 10.0 g Kr
How many moles of copper are equivalent to 3.44 x 1023 atoms of
copper?
A
0.571 moles
B
1.75 moles
C
5.41 x 1021 moles
D 5.71 x 1022 moles
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5/8/2012
Chemistry SOL Review— Molar Relationships
Stoichiometry
Chemistry SOL Review— Molar Relationships
Stoichiometry
For reaction calculations, the molar ratio is used.
For reaction calculations, the molar ratio is used.
Example:
How many moles of nitrogen will react with 9 moles of hydrogen to
produce ammonia according to this equation?
Example 2:
How many grams of nitrogen are needed to react with 2.0 grams of
hydrogen using this equation?
2N2(g) +3 H2(g) → 3NH3(g)
2N2(g) +3 H2(g) → 3NH3(g)
2 moles 3 moles
28.02 g 2.02 g
Given: 9 moles H2, Find moles N2
9 mol H2 x 2 mol N2 = 6 mol N2
3 mol H2
Given: 2.0 grams H2, Find grams N2
2.0 g H2
1
X
2 X 28.02
3 X 2.02
= 19 g N2
Mole ratio
Formaldehyde (H2CO) reacts with oxygen to form CO2 and H2O.
How many moles of CO2 will be produced from reacting 2 moles of
H2CO with oxygen?
A
1
B
2
C
4
D 8
 N2 + 3H2 → 2NH3
If 6 liters of hydrogen gas are used,how many liters of nitrogen gas will be
needed for the above reaction at STP?
A
2 liters
B
3 liters
C
4 liters
D 12 liters
 2KOH + H2SO4 → 2H2O + K2SO4
What mass of potassium hydroxide is required to react completely with
2.70 g of sulfuric acid to produce potassium sulfate and water?
A
4.73 g
B
3.09 g
C
2.36 g
D 1.54 g
Chemistry SOL Review— Molar Relationships

Solution Concentrations
Calculating molarity:
Memorize this equation: Molarity = moles/liters or M = mol
L
Memorize conversion factor: 1000 mL = 1 L
Some example of using this equation:
Example 1: the molarity of 2.0 moles of HCl in a 0.50 L solution of water is:
molarity = 2.0 mole HCl/0.50 L = 4.0 Molar or 4 M
Example 2: The molarity of 0.40 moles of HCl in a 300. mL L solution of
water is:
molarity = 0.40 moles HCl/0.300. L = = 1.3 M
Chemistry SOL Review— Molar Relationships
Solution Concentrations
Chemistry SOL Review— Molar Relationships
Solution Concentrations
Example 3:
You try one:
The molarity of 72.9 g of HCl in 5.0 liters of aqueous solution is:
What is the molarity of 1.2 grams LiF in a 50. mL aqeous solution?
Answer: first calculate the moles of HCl
72.9 g HCl
x 1 mol HCl
36.46 g HCl
Then calculate molarity of solution:
2.00 mol HCl/5.0 L = 0.40 M HCl
Answer: first calculate the moles of LiF
= 2.00 mol HCl
1.2 g LiF
x
1 mol LiF
= 0.046 mol LiF
25.94 g LiF
Then calculate molarity of solution (remember convert mL to Liters):
0.046 mol LiF/0.050 L = 0.95 M LiF
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Chemistry SOL Review— Molar Relationships
Solution Concentrations
Diluting concentrated solutions
Memorize: C1V1

Memorize: C1V1
= C2V2
•C1 and V1 are the beginning molarities and volumes
•C1 and V1 are the beginning molarities and volumes
•C2 and V2 are the ending molarities and volumes
•C2 and V2 are the ending molarities and volumes
•V1 and V2 can be in Liters or mLs, but must be the same units for both
•V1 and V2 can be in Liters or mLs, but must be the same units for both
Example:
You try one:
What is the molarity of a 10. mL sample of 2.0 M aqueous HCl diluted to
40. mL
How many milliliters of 6.0 Molar HCl are required to prepare 240 mL of
2.0 Molar HCl?
Answer:
Answer:
(2.0)(10.) = (M2)(40.) so M2 = 0.5 Molar HCl
(6.0)(V1) = (2.0)(240) so V1 = 80. mL HCl
How many milliliters of 2.00 M H2SO4 are needed to provide
0.250 mole of H2SO4?
A 125 mL
B 1.25 x 101 mL
C 8.00 x 103 mL
D 8.00 mL
What is the molarity of a solution prepared by dissolving 27.2 g
of sodium chloride in enough water to prepare 500.0 mL of
solution?
A 0.186 M
B 0.465 M
C 0.930 M
D 1.860 M
A solution contains 225 g of glucose, C6H12O6, dissolved in
enough water to make 0.825 L of solution. What is the molarity
of the solution?
A 0.66 M
B 0.97 M
C 1.03 M
D 1.52 M
Chemistry SOL Review--Molar Relationships
Chemical Equilibrium
Exothermic and Endothermic Reactions
Catalysts lower the Activation energy barrier, making reactions faster.
Exothermic reactions release heat
100
100
0
0
rxn progress >
A + B = AB + heat
rxn progress >
A + B + heat = AB
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Chemistry SOL Review--Molar Relationships
Chemical Equilibrium
Endothermic reactions absorb heat
Joules >

Diluting concentrated solutions
Joules >

= C2V2
Chemistry SOL Review— Molar Relationships
Solution Concentrations
Chemistry SOL Review--Molar Relationships
Chemical Equilibrium
Reversible Reactions
Reversible Reactions
Some reactions are REVERSIBLE, which means that they can go
backwards (from product to reactant)
Le Chatelier’s Principle: If a system at equilibrium is stressed, the
equilibrium will shift in a direction that relieves that stress.
Example: The reaction between nitrogen and hydrogen, where a “”
indicates a reversible reaction
Equilibrium will shift AWAY from what is added. Here, N 2 is added.
N2(g) + 3H2(g)  2 NH3(g) + heat
The forward reaction takes place at the same rate as the reverse
reaction. The equilibrium position of products and reactants depends on
the conditions of the reaction. If we change the reaction conditions, the
equilibrium changes.
N2
More “product” made
N2(g) + 3H2(g)  2 NH3(g) + heat
“UP UP AND AWAY!”
“UP UP AND AWAY!”
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5/8/2012
Chemistry SOL Review--Molar Relationships
Chemical Equilibrium
Chemistry SOL Review--Molar Relationships
Chemical Equilibrium
Reversible Reactions
Reversible Reactions
Le Chatelier’s Principle: If a system at equilibrium is stressed, the
equilibrium will shift in a direction that relieves that stress.
Le Chatelier’s Principle: If a system at equilibrium is stressed, the
equilibrium will shift in a direction that relieves that stress.
Equilibrium will shift AWAY from what is added. Here, NH 3 is added.
Equilibrium will shift TOWARDS what is removed. Here H 2 is removed.
More “reactants” made
NH3
H2
N2(g) + 3H2(g)  2 NH3(g) + heat
N2(g) + 3H2(g)  2 NH3(g) + heat
More “reactants”
made
“UP UP AND AWAY!”
Chemistry SOL Review--Molar Relationships
Chemistry SOL Review--Molar Relationships
Chemical Equilibrium
Chemical Equilibrium
Reversible Reactions
Le Chatelier’s Principle: If a system at equilibrium is stressed, the
equilibrium will shift in a direction that relieves that stress.
Methods to Speed up Reactions:
Equilibrium will shift TOWARDS what is removed. Here heat is
removed.
•Reduce the particle size
heat
•Use a catalyst
•Increase the heat
•Increase reactant concentration
N2(g) + 3H2(g)  2 NH3(g) + heat
More “product” made
In the reaction 2SO2 (g) + O2 (g)  2SO3 (g), which
change would cause the greatest increase in the
concentration of SO3?
A Decrease the concentration of SO2
B Decrease the concentration of O2
C Increase the concentration of SO2
D Increase the concentration of O2
 Which condition will cause a shift in
the equilibrium of the above reaction?
A Double the concentration of reactants and products
B Increase the reaction temperature
C Reduce the concentration of products and reactants by
10%
D Keep the reaction temperature constant

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Chemistry SOL Review--Molar Relationships
Acid/Base Theory
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Acids and Bases
Generic formula for acids = HX (HCl, HNO3, H2SO4)
Generic formula for bases = MOH where M is any metal (NaOH, KOH,
Ca(OH)2 Ammonia, NH3, is also a base.
Acid solutions have a pH less than 7
Basic solutions have a pH more than 7
Arrhenius acids:
sour
Taste _______
turn litmus paper red.
SAFETY NOTES
Arrhenius bases
bitter
Taste _______
slippery
Feel __________
Turn litmus paper blue.
If you spill acid or base on
yourself, rinse with lots of water.
Always add acid to water when
diluting (AAA)
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5/8/2012
Chemistry SOL Review--Molar Relationships
Acid/Base Theory

A
B
C
D
What is pH?
pH indicates the hydrogen ion molarity [H+] in a solution
pH = -log[H+]

What is represented by the pH of a solution?
A
Partial pressure of hydrogen ions in the solution
B
Electronegativity of dissociated hydrogen ions in the solution
C
Concentration of hydrogen ions in the solution
D Temperature of hydrogen ions in the solution

The hydrogen ion concentration is 1 x 10-7. What is the pH of this solution?
A
1
B
7
C
10
D 14
pOH indicates the hydroxide ion molarity [OH -] in a solution.
pOH = -log[OH-]
Example: A 1.0 x 10-3 molar solution of HCl would have a pH of ___
3
4
Example: A 1.0 x 10-4 molar solution of KOH would have a pOH of ___
Memorize: pH + pOH = 14.
6
Example: A solution with a pH of 8 will have a pOH of: ____.

Ulcers are often caused by an excess of stomach
acid. Milk of magnesia is often used to soothe the
irritation. Milk of magnesia is probably —
A an acid
B a base
C an indicator
D a colloid

The pH of a 0.1 molar aqueous solution of HCl
would equal —
A -1
B 1
C 11
D 13
Which pair of solutions would be acidic if mixed in equal quantities?
A and B
Solution A
B
C
D
B and C
B and D
pH
2
6
9
12
C and D
7