Unit 3 Packet: The Mole
WPHS Chemistry
Name
Unit 3
The Mole
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
Chemistry: Unit 3 Outline: The Mole
Assignment
WB Page Number
Podcast 3.1 (CB 1-5)
Online
Lab: Pennies
pg 5-6
Worksheet A
pg 13
Podcast 3.2 (CB 7-9)
Online
Lab: Mole Lab
Worksheet B (long)
pg 14-17
Mole Video (Dr. Don)
pg 12
Demo: Measure out 1 mole of
In class
NaCl, H2O, NaHCO3 and show
to your teacher
Podcast 3.3 (CB 11-13)
Online
Worksheet C
Pg 17-18
Worksheet D
Pg 19-20
Technology Lab
Teacher Handout
Lab: Magnesium and Oxygen
Pr 8-11
Formula
Score
Out of

100


100






100
100
THL 2: amount of Oxygen in
Pg 4
100
Air—do at home for parents
Review
Pg 22-23
Unit 2 Exam (You must score
In Class
100
85/100 to move to the next unit)
(You must score 85/100 on all assignments with a number to move to the next unit. For
those assignments with a check, you need to do it to the satisfaction of your teacher)
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
Visualizing Chemistry Notebook Set-Up: Chapter 7: Chemical Quantities
7-1: The Mole: A Measurement of Matter?
What is the mole (pg 171-173)
1
 Why was the mole unit created?
 What is Avagadro’s number and why is it so big?
7-2: Mole Mass and Mole Volume Relationships
Molar Mass—The Mass of one Mole (page 176-183)
3
 Define molar mass
 Read the sections on the mass of one mole and fill in this chart
Name
Formula
Show Work
5
7
9
Iron II hydroxide
Aluminum sulfate
Sodium bicarbonate
Dinitrogen pentoxide
The Volume of a mole of gas
 Write out the conditions for standard temperature and pressure
Converting between moles-grams-particles-liters
Leave this page blank for teacher directed notes
Converting between moles-grams-particles-liters
Leave this page blank for teacher directed notes
7.3: Percent Composition and Chemical Formulas
11 Percent composition (Continued from previous page) (188-190)
 Define Percentage composition
 Use sample problem 7-10 on page 189 to complete the table below
Chemical
Molar Mass
Percent 1st Element Percent 2nd
Element
FeSO4
NaClO3
K3PO4
C6H12O6
13
15
Molar mass
(g/mol)
Percent 3rd
Element
Use sample 7-12 on page 191 to do practice problem 34 on page 192
Derive a compound’s empirical formula from its percentage composition (page 192-193)
 Define empirical formula
 Copy down the following rhyme:
o Percent to mass
o Mass to mole
o Divide by small
o Times ‘til whole
Calculate the molecular formula of a compound from its empirical formula and from its formula mass (pg 194195)
 Define molecular formula
 Finish the following statement: Molecular formulas are _______ of empirical formulas
 Copy down Table 7.2 on page 194
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
Take Home Lab
Parent/Student Experiment
Title: Amount of Oxygen in Air
Subject/Concept: Chemistry - Combustion and Percent Composition
Purpose: The purpose of this activity is to observe the amount of oxygen required for a candle to burn in a
closed environment and then to calculate the amount of oxygen originally present.
Materials:
• small candle (emergency candles work well)
• food coloring
• shallow pan filled two-thirds with water
• glass jar
Procedure:
1. Attach the candle to the bottom of the shallow pan. A few drops of hot wax work nicely.
2. Place a piece of masking tape on the side of the jar from the top to the bottom. This will be used to
mark water levels during the experiment.
3. Fill the dish two-thirds with water and color the water.
4. Place the jar over the UNLIT candle, and mark the starting height of the water.
5. Light the candle and cover it quickly with the jar. Observe.
6. Mark the ending height of the water on the masking tape, and repeat the experiment several more
times.
7. Measure the original height of the air column in the glass and the ending heights of the air column.
Average the ending heights.
8. Calculate the amount of air (oxygen) used by the candle. This will be the difference between your
starting and ending heights of air.
9. Calculate the percent of air that is oxygen. This will be the amount of oxygen used divided by the
amount of total air to start x 100.
Questions:
1. What was the height of air in the jar at the beginning of the experiment?
2. What was the average height of air in the jar after the burn?
3. What was the difference in heights?
4. What was the percent of oxygen that you obtained? Compare this to the actual value of 21%.
5. Why does the water rise in the jar?
For Credit:
To receive credit, your parent or guardian must write a short note confirming that you performed
the experiment for them and explained the results to their satisfaction using the concept of combustion.
Attach your note to the back of this sheet.
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
PENNY COUNTING BY WEIGHING
PURPOSE: To make a model of counting by weighing.
MATERIALS: A handful of pennies, a balance
PROCEDURE:
1. Determine the average mass of a penny by weighing 25 pennies and dividing the total
mass by 25.
2. Repeat step 1 two more times with different pennies, and take the average of your
three results.
3. Weigh about three-fourths of you total number of pennies.
4. Calculate how many pennies you weighed.
5. Count the number of pennies in your sample and compare that to the number you
calculated in steps 3 & 4.
6. Repeat steps 3,4 and 5 with a different sample size.
DATA TABLE:
QUESTIONS:
1. Did the number of pennies you counted in the sample (step three) equal the number
you calculated by weighing (step two)? If there was not agreement, propose an
explanation.
2. Explain how you would use the balance to “count out” 185 pennies.
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
3. What is the advantage of using a larger sample size in step 1? What is a
disadvantage?
4. How are the pennies like atoms in this experiment?
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
Mole Lab: Making a precipitate of BaSO4
Background: The unit of measure for the amount of a substance is the mole. A mole is
6.02 x 1023 particles (such as atoms or molecules). The mass of one more of any
substance is found using the periodic table (calculate molar mass).
Purpose: The purpose of this lab is to measure chemical quantities.
Materials: small test tubes, balance, weigh boat, BaCl2, Na2SO4, H2O, centrifuge,
graduated cylinder
Calculations:
Convert moles of barium chloride to grams
Convert moles of sodium sulfate to grams
Procedure:
1. Weigh 0.0025 mole of barium chloride and place in one test tube
2. Weigh 0.0035 mole of sodium sulfate and place in another test tube
3. Add 3 mL of water to each test tube
4. Agitate (shake or tap) each mix until the chemical inside it dissolves
5. After both substances have completely dissolved combine them into one of the
test tubes (this will create a milky solution)
6. Place the test tube in the centrifuge, making sure that another group’s test tube is
directly across from your test tube and allow the centrifuge to run for 1 minute
7. Bring your test tube to your teacher to check the amount of precipitate and sign
your group’s papers
Questions:
1. What is the evidence that a chemical reaction has occurred?
2. When you mixed the two solutions, you created BaSO4. What is the name of this
chemical?
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
MAGNESIUM OXIDE PRODUCTION
Objectives: In this investigation, you will
 prepare magnesium oxide,
 calculate the percent composition of your product, and
 determine the product’s empirical and molecular formulas.
Equipment:
crucible and cover
Bunsen burner
ring stand
wash bottle
15 cm Mg ribbon
distilled water
tongs
clay triangle
iron ring
glass stirring rod
analytic balance
GOGGLES
Procedure:
1. Wash and dry your hands (moisture on your hands will react with the magnesium
ribbon).
2. Record the mass of a clean, dry crucible and cover.
3. Obtain a piece of magnesium ribbon approximately 15 cm long from your
instructor and scrape both sides of the magnesium with the scissor blade to
remove corrosion (when the corrosion is removed the Mg will appear shiny). Coil
the Mg loosely around a pencil. Remove the pencil, place the magnesium in the
crucible and record the mass of the magnesium, crucible and lid.
4. Place the crucible, cover and magnesium on a clay triangle as shown in the figure.
5. Adjust the crucible and cover on the clay triangle so that the lid is ajar. This
position will allow a steady flow of air into the crucible. Heat the crucible gently
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
for 3 minutes then strongly for 5 minutes. CAUTION: Do not look directly at
the burning magnesium. Allow the crucible to cool for 5 minutes.
6. Crush the contents of the crucible into powder using a glass stirring rod. Using
about 15 drops of water from a wash bottle, rinse powder from the the stirring rod
into the crucible. Note any odor as you add the water.
Odor:___________________
7. Heat the crucible strongly, without the cover, for 5 minutes to dry the residue.
Cool the crucible and contents for 5 to 10 minutes. It should be cool enough to
NOT burn your hand. Record the mass of the crucible, cover, and contents.
ANALYSIS: Show all measurements and calculated numbers in the spaces provided in
the data table. (Show units and substance symbol or formula for each measurement taken
or number calculated.)
Measurement
mass of crucible, cover, and Mg before heating
mass of empty crucible and cover
mass of magnesium
mass of crucible, cover and residue after heating
mass of residue (magnesium oxide produced)
moles of oxygen in the magnesium oxide residue
moles of magnesium in the magnesium oxide residue
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
Calculations:
Calculate the percent composition of magnesium oxide (write the formula, balancing the
charges of the Mg ion and the O ion, then find the percent composition by mass).
From your measured value of the mass of residue in your data table, calculate the moles
of magnesium and of oxygen in your sample of residue.
Using the moles calculated above; calculate the empirical formula for your sample of
magnesium oxide.
Using the empirical formula found above, what is its molecular formula if the molar mass
is 40.3 g/mol?
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
Questions
1. Does the magnesium in your crucible gain or lose mass? Explain.
2. How would your final ratio change if not all of the magnesium had reacted?
3. How would your final ratio change if there were still some water in the
crucible after you stopped heating it?
4. Does your calculated formula for magnesium match the predicted formula
(questions #6)?
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
The World of Chemistry: Episode 11 - The Mole
1.
Why is it important to use the correct amount of materials in a chemical reaction?
2.
What names are given to the materials at the beginning and end of a chemical
reaction?
3.
Atoms and molecules are extremely small. How do chemists "count" them? Can
you think of an everyday application of this?
4.
a. What did early chemists discover about reactions involving the combination of
gases?
b. How did Avogadro explain this?
5.
How may a chemical equation such as H2 + Cl2  2 HCl be interpreted?
6.
What is true about the mass of a compound?
7.
What is the numerical value for Avogadro's Number?
8.
When the I V solutions were prepared, quality control was involved. What is quality
control?
9.
Why did using twice as much magnesium not produce twice as much hydrogen in
the demonstration?
10. What ratio of starting materials was found to produce the best epoxy resin?
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Unit 3 Packet: The Mole
WPHS Chemistry
Name
Mole Worksheet
Molar Relationships
Part A:
Find the molar mass of the following compounds: Show work and include units
1. CO2
11. Lead II sulfate
2. Fe2O3
12. Lead II Sulfite
3. AgCl
13. Lead II Sulfide
4. Ca3(PO4)2
5. W3(PO3)5
14. Copper I Sulfide
6. Fe(C2H3O2)2
15. Copper II Sulfite
7. Calcium Carbonate
8. Lead IV Sulfate
9. Lead IV Sulfite
10. Lead IV Sulfide
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Worksheet B:
Directions: Answer the following questions. Set-up all problems using the factor-label
method of dimensional analysis and show all your work and units.
1. What is the mass of 7.50 moles of sulfur dioxide (SO2)?
2. How many moles are there in 250.0 grams of sodium phosphate (Na3PO4)?
3. How many grams of potassium sulfate (K2SO4) are there in 25.3 moles?
4. How many atoms are in 1.5 moles of neon?
5. How many moles of SF6 are there in 4,595,000,000,000,000,000 molecules of
SF6?
6. What is the volume of 0.38 moles of any gas at STP?
7. Calculate the number of moles in 32.2-L of NH3
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
8. Calculate the number of moles in 5.45x1025 atoms of Zn
9. Calculate the number of grams in 3.25-mol of AgNO3
10. What is the mass of 51 liters of oxygen gas?
11. What volume would be occupied by 9.45 x 1024 molecules of CO2 gas at STP?
12. How many calcium atoms would be in a 100 gram sample of calcium metal?
13. How many grams are in 5.6 x 1023 atoms of Zinc?
14. Calculate the number of molecules in 4.56-g of Pb(NO3)2
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
15. Calculate the number of liters in 3.25-g of NH3
16. Calculate the number of liters in 5.43x1025 molecules of H2
17. Calculate the number of grams in 3.54-L of CO2
18. Calculate the number of grams in 9.7x1022 molecules of CH3CH2OH
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Part C: Percentage Composition
1. Calculate the % composition of Li2O.
2. What is the percentage composition of a carbon-oxygen compound, given that a 95.2 g
sample of the compound contains 40.8 g of carbon and 54.4 g of oxygen?
3. What is the percentage composition of N2O4?
4. What is the percentage composition of a compound made from 28 grams of nitrogen
and 32 grams of oxygen?
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
5. What is the percentage composition of a carbon-hydrogen-fluorine compound which
contains 7.2 grams of carbon, 11.4 grams of fluorine, and 1.8 grams of hydrogen?
6. Find the percentage composition of Na2SO4?
7. If a compound is formed from 60.0 liters of nitrogen gas, N2, (at STP) and 180 liters
of hydrogen gas, H2, (at STP), what is its percentage composition?
8. Find the percentage composition of a compound formed when 0.4 moles of potassium
are reacted with 8.96 liters of O2 gas and 2.41 x 1022 atoms of S.
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Part D: Empirical and Molecular Formulas
1. Determine the empirical formula of a compound with 72.4% Fe and 27.6%
Oxygen.
2.
Determine the empirical formula of a compound with 65.2% Sc and 34.8%
O
3. Determine the empirical formula of a compound with 52.8% Sn, 12.4% Fe,
16% C and 18.8% N.
4. Determine the empirical formula of a compound that contains 2.61-g of
carbon, 0.65-g of hydrogen, and 1.74-g of oxygen
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
5. Determine the molecular formula for a compound that contains 12.2-g
Nitrogen, 27.8-g Oxygen, and a molecular mass of 92.0 g/mol.
6. Determine the molecular formula for a compound that contains 94.1%
oxygen and 5.9% hydrogen and a molecular mass of 34 g/mol.
7. Determine the molecular formula for a compound that contains 22.5% Na,
30.4% P and 47.1% O and a molar mass of 306 g/mol
8. Determine the molecular formula of a compound that contains 76% iodine
and 24% oxygen and has a molar mass of 334g/mol.
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
9. Determine the molecular formula of a compound that contains 48.6%
carbon, 8.1% hydrogen, and 43.2% oxygen and has a molar mass of 296g/mol.
10. Determine the molecular formula of a compound that contains 0.993-g
nitrogen, 1.27-g carbon, 0.213-g hydrogen, 2.52-g chlorine and has a molar
mass of 423-g/mol.
11. A sample of TNT, a common explosive is analyzed and found to contain 1.03g of nitrogen, 0.220-g hydrogen, and 1.76-g of carbon. The molar mass is 123
g/mol. What is the molecular formula?
12. Azobenzene is an important intermediate in the manufacture of dyes. It
contains 79.1% carbon, 5.55% hydrogen, and 15.4% nitrogen. It has a molar
mass of 182-g/mol. What is the molecular formula?
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Unit 3 Review
Be sure to show all of your work. Make sure that you box your answer and that you have
units!
1) Determine the molar mass of the following compounds.
a) Nitrogen dioxide
b) NH4NO3
2) Convert the following:
a) 4.53 moles of carbon monoxide to grams
b) 0.0067 L of chlorine gas (Cl2) at STP to moles
c) 2.41  1024 molecules of (NH4)SO3 to moles
3) Convert the following:
a) 20.6 L of SO2 to grams
b) 4.44 g of iron (II) oxide molecules
c) 8.322 x 1024 molecules of N2 to L
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
4) Determine the percent composition of CuSO4
5) Determine the empirical formula of a sample that has: 21.6% sodium (Na), 33.3%
chlorine (Cl), and 45.1% oxygen (O)
Empirical Formula
6) Determine the molecular formula of the following compound:
Nitrogen = 30.4%
Oxygen=69.6%
Molecular weight = 92 g/mol
Empirical Formula
Molecular Formula
- 23 -
WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Mole Worksheet
KEY
Name____________________
Molar Relationships
Period____
Directions: Answer the following questions on a separate sheet of paper. Set-up all
problems using the factor-label method of dimensional analysis and show all your work
and units.
1. What is the mass of 7.50 moles of sulfur dioxide (SO2)?480g
7.5mol 64g
x
 480g
1
1mol
2. How many moles are there in 21.4 grams of nitrogen gas (N2)? 0.764mol
21.4g 1mol
x
 0.764mol
1
28g

3. How many moles are there in 250.0 grams of sodium phosphate (Na3PO4)? 1.52mol
250g 1mol
x
 1.52mol
1
164g

4. How many grams of potassium sulfate (K2SO4) are there in 25.3 moles? 4402g
25.3mol 176g
x
 4402g
1
1mol
5. How many atoms are in 1.5 moles of neon? 9.0x1023atoms


1.5mol 6.02x10 23 atoms
x
 9.0x10 23 atoms
1
1mol
6. How many moles of SF6 are there in 4,595,000,000,000,000,000 molecules of SF6?
7.633x10-6mol
4.595x1018 molec
1mol
6
x

7.633x10
mol
1
6.02x10 23 molec
7. How many molecules are there in 7.50 moles of sulfur dioxide (SO2)?
4.52x1024molec

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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
7.5mol 6.02x10 23 atoms
x
 4.52x10 24 atoms
1
1mol
8. What volume is occupied by 7.50 moles of sulfur dioxide gas (SO2) at STP? 168L

7.50mol 22.4L
x
168L
1
1mol
9. 49.28 L of oxygen gas is how many moles of gas?2.20mol




49.28L 1mol
x
 2.20mol
1
22.4L
10. What is the volume of 0.38 moles of any gas at STP? 8.5L
0.38mol 22.4L
x
 8.5L
1
1mol
11. What is the mass of 51 liters of oxygen gas? 73g
51L 1mol 32g
x
x
 73g
1 22.4L 1mol
12. What volume would be occupied by 9.45 x 1024 molecules of CO2 gas at STP? 351L
9.45x10 24 molec
1mol
22.4L
x
x
 351L
23
1
6.02x10 molec 1mol
13. How many calcium atoms would be in a 100 gram sample of calcium metal?
1.5x1024atoms

100g 1mol 6.02x10 23 atoms
x
x
 1.5x10 24 atoms
1
40g
1mol
14. How many grams are in 5.6 x 1023 atoms of Zinc? 60.g

- 25 -
WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
4.595.6x10 23 molec
1mol
65g
x
x
 60.g
23
1
6.02x10 molec 1mol

- 26 -
WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Mole WS 2
Two Step Problems
1. Calculate the number of moles in 45.5-g of NH4Cl
MM  14  4  35.5 
53.5g
1mol
45.4g 1mol
x
 0.849mol
1
53.5g
2. Calculate the number of moles in 32.2-L of NH3

32.3L 1mol
x
1.44mol
1
22.4L
3. Calculate the number of moles in 5.45x1025 atoms of Zn
5.45x10 25 atoms
1mol
x
 90.5mol
1
6.02x10 23 atoms
4. Calculate the number of grams in 3.25-mol of AgNO3

MM  107  14  3x16 

169g
1mol
3.25mol 169g
x
 549g
1
1mol
5. Calculate the number of liters in 0.0045-mol of N2




0.0045mol 22.4L
x
 0.101L
1
1mol
6. Calculate the number of molecules in 0.00325-mol of O2
0.00325mol 6.02x10 23 molec
x
 1.96x10 21 molec
1
1mol
Three Step Problems
7. Calculate the number of molecules in 4.56-g of Pb(NO3)2
331g
1mol
23
4.56g 1mol 6.02x10 molec
x
x
 8.29x10 21 molec
1
331g
1mol
MM  207  14 x2  16x6 
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
8. Calculate the number of liters in 3.25-g of NH3
17g
1mol
3.26g 1mol 22.4L
x
x
 4.30L
1
17g 1mol
MM  14  3 
9. Calculate the number of liters in 5.43x1025 molecules of H2

5.43x10 25 molec
1mol
22.4L
x
x
 2020L
1
6.02x10 23 molec 1mol
10. Calculate the number of grams in 3.54-L of CO2
44g
1mol
3.54L 1mol 44g
x
x
 6.95g
1
22.4L 1mol
MM  12  16x2 

11.
Calculate the number of grams in 9.7x1022 molecules of CH3CH2OH
46g
1mol
9.72x10 22 molec
1mol
46g
x
x
 7.4g
23
1
6.02x10 molec 1mol
MM  12x2  6  16 

12.

Calculate the number of molecules in 5.42-L of O2
5.42L 1mol 6.02x10 23 molec
x
x
 1.46x10 23 molec
1
22.4L
1mol

- 28 -
WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Part II
1. Calculate the % composition of Li2O.
Li2O :: MM  7x2  16  30g /mol
14
Li 
x100  46.7%
30
16
O
x100  53.3%
30
2. What is the percentage composition of a carbon-oxygen compound, given that a 95.2 g
sample
of the compound contains 40.8 g of carbon and 54.4 g of oxygen?

40.8
C
x100  42.9%
95.2
54.4
O
x100  57.1%
95.2
3. What is the percentage composition of N2O4?
N 2O4 :: MM  14 x2  16x2  60
28
N
x100  46.7%
60
O  100  46.7  53.3%

4. What is the percentage composition of a compound made from 28 grams of nitrogen
and 32 grams of oxygen?

28
28

x100  46.7%  Nitrogen
(28  32) 60
Oxygen  100  46.7  53.3%

- 29 -

WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
5. What is the percentage composition of a carbon-hydrogen-fluorine compound which
contains7.2 grams of carbon, 11.4 grams of fluorine, and 1.8 grams of hydrogen?
7.2  11.4  1.8  20.4
7.2
x100  35.3%
20.4
1.8
H
x100  8.9%
20.4
11.4
F
x100  55.9%
20.4
C
6. Find the percentage composition of Na2SO4?

142g
MM  23x2  32  16x4 
1mol
23x2
Na 
 x100  32.3%
142
32
S
x100  22.5%
142
16x4
O
x100  45.1%
142
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
BONUS PROBLEMS:
7. If a compound is formed from 60.0 liters of nitrogen gas, N2, (at STP) and 180 liters
of hydrogen gas, H2, (at STP), what is its percentage composition?
Convert  to  grams
60.0LN 2 1mol 28g
x
x
 75gN 2
1
22.4L 1mol
180LH 2 1mol
2g
x
x
 16.1gH 2
1
22.4L 1mol
Total  mass  75  16.1  91.1g
75
N
x100  82.4%  H  100  82.4  17.6%
91

8. Find the percentage composition of a compound formed when 0.4 moles of
potassium are reacted with 8.96 liters of O2 gas and 2.41 x 1022 atoms of S.
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Convert  to  grams
0.4molK 39
x
 15.6gK
1
1mol
8.96LO2 1mol 32g
x
x
 12.8gO2
1
22.4L 1mol
2.41x10 22 molecS
1mol
32g
x
x
 1.28gS
1
6.02x10 23 molec 1mol
Total  Mass  1.28  12.8  15.6  29.7g
39
K
x100  52.5%
29.7
12.8
O
x100  43.1%
29.7
1.28
S
x100  4.4%
29.7

- 32 -
WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Part E: Empirical and Molecular Formulas
1. Determine the empirical formula of a compound with 72.4% Fe and 27.6%
Oxygen.
72.4gFe 1molFe
x
 1.29molFe
1
56gFe
27.6gO 1molO
O:
x
 1.725molO
1
16gO
1.29molFe
 1x3  3
1.29mol
1.725molO
 1.33x3  4
1.29mol
Fe3O4
Fe :
+6
2. Determine the empirical formula of a compound with 65.2% Sc and 34.8% O

65.2gSc 1molSc
x
 1.45molSc
1
45gSc
34.8gO 1molO
O:
x
 2.175molO
1
16gO
1.45molSc
 1x2  2
1.45mol
2.175molO
 1.5x2  3
1.45mol
Sc 2O3
Sc :
+6
3. Determine the empirical formula of a compound with 52.8% Sn, 12.4% Fe, 16%
C and 18.8% N.

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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
52.8gSc 1molSc 0.444molSn
x

2
1
119gSc
0.221
12.4gFe 1molFe 0.221molFe
Fe :
x

1
1
56gFe
0.221
16gC 1molC 1.33molC
C:
x

6
1
12gC
0.221
18.8gC 1molN 1.34molN
N:
x

6
1
14gN
0.221
Sn :
+8
Sn 2 FeC6 N 6
4. Determine the molecular formula for a compound that contains 12.2-g Nitrogen,
27.8-g Oxygen, and a molecular mass of 92.0 g/mol.

12.2gN 1molN
0.87molN
x
 0.87molN ::
1
1
14gN
0.87mol
27.8gO 1molO
1.74molO
O:
x
 1.74molO ::
2
1
16gO
0.87mol
EF  NO2 :: EM  46 :: MM  92
Factor  2
N:
+
NO2 x2  N 2O4
8

5. Determine the molecular formula for a compound that contains 94.1% oxygen
and 5.9% hydrogen and a molecular mass of 34 g/mol.
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
5.9gH 1molH
5.9molN
x
 5.9molH ::
1
1
1gH
5.9mol
94.1O 1molO
5.9molO
O:
x
 5.9molO ::
1
1
16gO
5.9mol
EF  HO :: EM  17 :: MM  34
Factor  2
H:
+8
HOx 2  H 2O2
6. Determine the molecular formula for a compound that contains 22.5% Na, 30.4%
P and 47.1% O and a molar mass of 306 g/mol

22.5gNa 1molNa
0.978molNa
x
 0.978molNa ::
1
1
23gNa
0.98mol
30.4gP 1molP
0.98molP
P:
x
 0.98molP ::
1
1
31gP
0.98mol
47.1O 1molO
2.94molO
O:
x
 2.94molO ::
3
1
16gO
0.98mol
EF  NaPO3 :: EM  102 :: MM  306
Factor  3
NaPO3 x3  Na3 P3O9
Na :
+8

Total=44
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
8. Determine the molecular formula of a compound that contains 76% iodine
and 24% oxygen and has a molar mass of 334g/mol.
76 g 1mol


x
 0.598mol / 0.598mol  1
I 
1 127 g

 x2


24 g 1mol
x
 1.5mol / 0.598mol  2.5 
 O 
1
16 g


I 2O5
MM  334 : EM  334
MF  I 2O5
9. Determine the molecular formula of a compound that contains 48.6%
carbon, 8.1% hydrogen, and 43.2% oxygen and has a molar mass of 296g/mol.


48.6 g 1mol
C 
x
 4.05mol / 2.7 mol  1.5 
1
12 g




8.1g 1mol
H 
 x2
x
 8.1mol / 2.7 mol  3
1
1
g




43.2 g 1mol
 O 
x
 2.7 mol / 2.7 mol  1 
1
16
g


C3 H 6O2
MM  296 : EM  74(multiple 4)
MF  C12 H 24O8
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
10. Determine the molecular formula of a compound that contains 0.993-g
nitrogen, 1.27-g carbon, 0.213-g hydrogen, 2.52-g chlorine and has a molar
mass of 423-g/mol.
0.993g 1mol


x
 0.0709 / 0.0709mol  1
N 

1
14 g




1.27 g 1mol
C

x

0
.
105
mol
/
0
.
0709
mol

1
.
49


1
12 g

 x2


0.213g 1mol
x
 0.213mol / 0.0709mol  3 
H 
1
1g




2.52 g 1mol
x
 0.0709mol / 0.0709mol  1
 Cl 
1
35.5 g


N 2C3 H 6Cl2
MM  423 : EM  141(multiple3)
MF  N 4C6 H12Cl4
11. A sample of TNT, a common explosive is analyzed and found to contain 1.03g of nitrogen, 0.220-g hydrogen, and 1.76-g of carbon. The molar mass is 123
g/mol. What is the molecular formula?


1.03 g 1mol
N 

x
 0.0736mol / 0.0736mol  1
1
14 g




0.220 g 1mol
H 
x
 0.220mol / 0.0736mol  2.99 
1
1g




1.76 g 1mol
 C 

x
 0.147mol / 0.0736mol  2
1
12
g


NH 3C 2
MM  123 : EM  41(multiple3)
MF  N 3 H 9C6
- 37 -
WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
12. Azobenzene is an important intermediate in the manufacture of dyes. It
contains 79.1% carbon, 5.95% hydrogen, and 15.4% nitrogen. It has a molar
mass of 182-g/mol. What is the molecular formula?


79.1g 1mol
C 
x
 6.59mol / 1.1mol  6 
1
12 g




5.95 g 1mol
H 
x
 5.95mol / 1.1mol  5 
1
1g




15.4 g 1mol
 N 
x
 1.1mol / 1.1mol  1 
1
14
g


C6 H 5 N
MM  182 : EM  91(multiple 2)
MF  C12 H 10 N 2
- 38 -
WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
Answer Key
1.
Why is it important to use the correct amount of materials in a chemical reaction?
If too little is used the reaction may not proceed very far. The use of too much chemical
may result in waste.
2.
What names are given to the materials at the beginning and end of a chemical
reaction?
Reactants andproducts.
3.
Atoms and molecules are extremely small. How do chemists "count" them? Can
you think of an everyday application of this?
They weigh them. If you know the number of nails or screws in a given mass, it is
quic*er to weigh them instead of counting them individualy.
4.
a. What did early chemists discover about reactions involving the combination of
gases?
They combined in small whole number ratios.
b. How did Avogadro explain this?
Equal volumes of gases funder the same conditions) contain equal numbers of particles.
5.
How may a chemical equation such as H2 + Cl2 2 HCl be interpreted?
It may be interpreted at the molecular basis or in terms of moles.
6.
What is true about the mass of a compound?
It is equal to the sum of the masses of the individual atoms in the compound.
7.
What is the numerical value for Avogadro's Number?
6.02 X 1023
8. When the I V solutions were prepared, quality control was involved. What is quality
control?
The testing of a manufactured product to determine if it contains what it is supposed to
contain.
9.
Why did using twice as much magnesium not produce twice as much hydrogen in
- 39 -
WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
the demonstration?
The hydrochloric acid was used up. The magnesium will be totally consumed only if
twice as many moles of acid are present. The hydrochloric acid became the limiting
reagent.
10. What ratio of starting materials was found to produce the best epoxy resin?
A one - to - one ratio.
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- 40 -