Unit 4 Packet - Page 1 of 16
Honors Chemistry - Unit 4
Chapters 3 & 7 – The Mole – Math with Chemical Formulas
Voc. Assignment Due:
Quiz Date(s): TBA
Problem Set Due:
Test Date:
**VOCABULARY Assignment**
(Use the Study Skills Section of your textbook (in the appendix) to assist you in making a Concept
Map from these vocabulary items/concepts):
molecular mass
formula mass
percent composition
empirical formula
formula unit
ionic compound
Avogadro’s number (constant)
hydrate
molecular formula
molecular compound
molarity
mole
FORMULA/CONSTANTS to be memorized
Molar mass conversion; *Avogadro’s number; *Molarity;
Steps for empirical formula/ molecular formula problems
OBJECTIVES:
 Be able to perform math functions with and without your calculator using correct scientific notation.
 Be able to find molecular/formula mass using the periodic table.
 Be able to calculate Molarity.
 Be able to calculate percent composition.
 Be able to determine empirical and molecular formulas using lab data.
Percent to mass; mass to mole; divide by small; multiply to whole!
 Understand the mole and Avogadro’s number.
 Be able to convert to/from atoms, ions, molecules, moles and grams.
Guided Note-Taking for THE MOLE!
What is a mole?
 “Official Definition”
 the amount of a substance that contains as many particles as there are atoms in exactly 12g
of carbon-12
 A mole is a counting unit
 just like a dozen
 other examples…..
Avogadro’s Number
 Constant
 the number of particles in exactly one mole of a pure substance
6.02 X 1023
Memorize this Number
1 mol = 6.02 X1023 of anything
But most often the mole is used with atoms, ions, formula units or molecules
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Examples of Conversion Factors:
1 mol
6.02 X 1023 atoms
1 mol
6.02 X 1023
ions or formula units
1 mol
6.02 X 1023
molecules
Molar Mass
 Mass in g of 1 mole of anything
 For

, the
is equal to the
1 mol
atomic wt. (g)
Molar Mass Examples:
1 mol C
12.0 g C
and
.
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You try:
1 mol Ca
g Ca
1 mol Fe
g Fe
Now, you have Two conversion Factors for a mole…..
Avogadro’s number
1 mol
and
6.02 X 1023 atoms, ions, formula units, or molecules
Example 1
How many g in 2.0 mol of He?
Example 2
How many moles in 3.01 X 1023 atoms Ag?
Example 3
What is the mass of 1.20 X 108 atoms of Cu??
You try:
Convert 11.5 g B to moles B
Convert 8.0 X 1019 atoms of Ag to g
Formula Mass/Molecular Mass/Molar Mass
 Sum of masses in a compound
Example: Molar Mass of sodium chloride NaCl
Example: Molar Mass of Ca(NO3)2
You try: Calculate the molar mass of sodium phosphate Na3PO4
Molar mass
1 mol
?g
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Calculate the molar mass for the following:
Molar mass can be used as conversion factors!
1 mol NaCl
58.44g NaCl
1 mol MgCl2
95.21g MgCl2
Example: How many mol in 127g barium chloride?
1 mol Ca(NO3)2
164.1g Ca(NO3)2
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Guided Note-Taking on Percent Composition
 Percent composition is the percent by mass of each element in a compound.
 Percent composition is the same, regardless of the size of the sample.
Percent Composition Calculations
% comp = mass of element
X 100% = % element in the compound
molar mass of cpd
Example: Find the % composition of Cu2S
 First, find the molar mass:
 Next, find the % of each element
 Next, check your work – do the %s add up to 100?
You try:
1) barium chloride
Answer: barium 65.90%; chloride 34.10%
2) sodium phosphate
Answer: sodium 42.07%; phosphorus 18.89%; oxygen
39.04%
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Guided Note-Taking on Empirical Formulas
 Empirical Formula = Simplest Formula
To find the empirical formula from data:
1. Assume 100% sample; change % to grams for each element (% to mass)
2. Find moles from the grams of each element (mass to moles)
3. Find the smallest whole # ratio by dividing by the smallest number of moles
(divide by small)
4. If necessary, multiply to get rid of fractions. (multiply to whole!)
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Example 1: A compound is 78% B and 22% H. What is the empirical formula?
First, change % to grams and find moles:
Next, divide all mole numbers by the smallest number of moles:
Finally, use these whole numbers as the number of each individual element. They are
the subscripts.
Example 2:
 Analysis shows a compound to contain 26.56% K, 35.41% Cr, and 38.03% O.
Find the empirical formula of this compound:
 First (always!) assume 100g sample, convert % to g and then find moles of each element.
Next, Conversion to moles:
Next, divide all numbers by the smallest whole number to find the smallest whole number
ratios:
 So, if you have:
multiply all by:
.25 or .75
4
.33 or .66
3
.50
2
 For our example:
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You Try:
What is the empirical formula if we have a sample containing 66.0% Ca and 34.0% P?
Answer: Ca3P2
You Try:
Find the empirical formula of a compound with 32.38% Na; 22.65% S; and 44.99% O.
Answer: Na2SO4
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Molecular Formula
Molecular Formula = Actual Formula
Example:
C2H6
molecular
MF = (EF)x
CH3
empirical
where X =
Molecular mass
Empirical mass
Example:
The empirical formula of a compound was found to be P2O5. Experimentation shows that the molar mass
of this compound is 283.89 g/mol. What is the compound’s molecular formula?
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Guided Note-Taking on Moles in Solution (Molarity)
 Molarity is the term used for moles dissolved in solution
 Symbol for Molarity = M
 Definition – moles of solute per liter of solution
 Formula
M=
moles solute (mol)
liter solution (L)
Example 1: What is the molarity of a 0.5L solution containing 2 moles of NaCl?
Example 2:
What is the molarity of a 250 mL solution containing 12.7 g of lithium bromide?
Example 3: How would you make 500mL of a 0.32M solution of LiBr and water?
You try:
1) Calculate the M of a 700. mL solution of 23.2g calcium chloride
2) How would you make a 0.2 L solution of 0.50 M CaCl2 solution?
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CONVERSION WORKSHEET
NAME:____________________________
A. Convert the following:
1. 1.20 x 1025 atoms of N to moles
2. 11.5 g of carbon to moles
3. 1.00 x 1026 atoms of Tl to grams
4. 0.400 moles of Cd(IO3)2 to formula units
5. 76.0 g of Ca to moles
6. 46.0 g of potassium nitride to formula units
7. 1.00 x 1023 formula units of CsBr to grams
8. 3.00 moles of Cl to grams
9. 9.30 moles of carbon dioxide to molecules
10. 8.00 x 1019 formula units of copper (II) sulfate to grams
11. 34.2 g of trisulfur dioxide to moles
12. 3.01 x 10 23 atoms of Mg to moles
13. 2.1 g of Ni to atoms
B. Molarity Practice
14. What is the molarity of the following?
a. 5.23 g Fe(NO3)2 in 100 ml of solution.
b. 8.55 g of ammonium iodide in 0.5 L of solution.
c. 3.2 kg of cobalt (II) sulfate in 4.3 L of solution.
15. Describe the preparation of the following:
a. 200 ml of 3.0 M NiCl2
b. 1 L of 1.5 M AgF
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Chapter Seven– Practice Sheet
CONVERSIONS
1. How many moles is 23.8 g of dinitrogen pentoxide?
2. How many formula units in 27 moles of iron (II) acetate?
3. How many g in 2.5 x 10 21 formula units of Calcium chloride?
4. How many molecules in 32.5 g of water?
PERCENT COMPOSITION
Find the percent composition of the following:
5. KNO3
6. Mg(NO3)2
7. The % of O in CuSO4
Empirical, Molecular, and Molarity
8. Analysis of a sample of sulfuric acid shows it to contain 0.17 g of hydrogen, 2.82 g of sulfur,
and 5.67 g of oxygen. What is the empirical formula for this compound?
9. Analysis of a salt results in the following composition: 3.47 g of Na, 2.12 g of N and 7.27 g of
oxygen. What is the simplest formula of this salt?
10. A barium salt is found to contain 21.93 g of barium, 5.12 g of sulfur and 10.24 g of O. What is
the empirical formula?
11. A compound contains: 26.7 % C, 2.2 % H and 71.1 % O. The molecular weight of the
compound is 90. What is the compound’s molecular formula?
12. A certain compound contains only C, H, and O. If 54.6 % is C and 9.0 % is H and the
molecular weight is 176, what are the compounds empirical and molecular formulas?
13. The percentage composition of ethane gas is 80.0 % C and 20.0 % H. The molecular weight
for ethane is 30. What is the molecular formula for this compound?
14. What is the M of 32.3 g of calcium chloride in 750 ml of solution?
15. How do you prepare 600 ml of 1.25 M CuO ?
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REVIEW – Chemistry Unit Four
1. How many moles are present in 114.95 g of nitrogen dioxide?
2. How many moles of nitrate are present in one mole of magnesium nitrate?
3. How many formula units in 64.3 g of lithium sulfate?
4. What is the molarity of 9.94 g of cobalt (II) sulfate in 250. ml of solution?
5. How would you prepare 250. ml of a 0.002 0 M solution of Cd(IO3)2?
6. What is the percentage of nitrogen in urea, CO(NH2)2?
7. A compound contains 27.3 g of C and 72.7 g of O. What is the empirical formula for this
compound?
8. Benzoic acid is a compound used as a food preservative. The compound contains 68.8 % C,
4.95 % H and 26.2 % O by mass. What is the compound’s empirical formula?
9. Ascorbic acid, also known as Vitamin C, has a percentage composition of 40.9 % carbon, 4.58
% hydrogen, and 54.5 % oxygen. Its molecular mass is 176.1 u. What is its molecular formula?
ANSWERS:
1. 2.5 mol NO2
2. 2 moles
3. 3.52 x 1023 formula units Li2SO4
4. 0.257 M CoSO4
5. Add 0.231 g of Cd(IO3)2to enough water to make 250. ml of solution.
6. 46.7 % N
7. CO2
8. C7H6O2
9. C6H8O6
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Unit 4 Problem Set –Review
Name:
Pd:___
First and last name please!
You must show work for credit – put final answer on the blank provided include units!
1. Name the following compounds:
a. Fe(C2H3O2)2
b. Mg(NO2)2
c. P3S2
d. CrPO4
e. H2SO4
f. SO3
g. BaCl2
h. H2CO3
i. H3PO4
j. N2O5
2. Write formulas for the following:
a. cobalt (II) nitrate
b. carbon tetrabromide
c. strontium chloride
d. iron (III) sulfate
e. nitric acid
f. calcium sulfide
g. chromium (III) nitride
h. hydrochloric acid
i. dinitrogen trioxide
j. acetic acid
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3. Fill in the following table:
Element/ion
Atomic
Number
Atomic
Mass
Mass
Number
# of
protons
# of
neutrons
# of
electrons
Fe
K+
27
25
O2Strontium-89
4. According to Guinness Book of World Records the fastest time for circling the bases is 13.3
seconds, set by Evar Swanson in 1932. Assuming the distance he traveled around the bases was
exactly 360 ft. perform the following calculations:
A. Calculate the velocity of the runner in meters per second and km per hour.
B. At this speed, how long would it take this runner to run 2 miles. (Assume this person can
maintain this speed for this distance!)