Unit 3 Packet: The Mole
WPHS Chemistry
Name
Unit 3
The Mole
-1-
Unit 3 Packet: The Mole
WPHS Chemistry
Name
Chemistry: Unit 3 Outline: The Mole
Assignment
Can only be done in class?
Podcast 3.1 - The Mole
Worksheet 3.1
Lab: Pennies
Yes
Podcast 3.2 – Molar Mass
Worksheet 3.2
Podcast 3.3 – Mole Conversion
(One Step)
Worksheet 3.3
Podcast 3.4 – Mole Conversion
(Two Steps)
Worksheet 3.4
Lab: Mole Lab
Yes
Mole Video (Dr. Don)
Demo: Measure out 1 mole of
Yes
NaCl, H2O, NaHCO3 and show
to your teacher
Podcast 3.5 % - Composition
Worksheet 3.5
Podcast 3.6 - Empirical Formula
Worksheet 3.6
Podcast 3.7 – Molecular Formula
Worksheet 3.7
Lab: Magnesium and Oxygen
Yes
Empirical Formula
Review
Unit 3 Exam (You must score
Yes
75/100 to move to the next unit)
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
Unit 3 Packet: The Mole
WPHS Chemistry
Name
Unit 3 Vocabulary
Mole
Avogadro’s Number
Representative Particle
Atomic Mass/Gram Atomic Mass)
Molecular Mass/Gram Molar Mass
Gram Formula Mass
Molar Mass
STP
Molar Volume
Percent Composition
Empirical Formula
Molecular Formula
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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 five) equal the number you
calculated by weighing (step four)? 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?
-5-
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, CaCl2, Na2SO4, H2O, centrifuge, graduated
cylinder
Calculations:
Convert moles of calcium chloride to grams
Convert moles of sodium sulfate to grams
Procedure:
1. Weigh 0.0025 mole of calcium chloride and place in one test tube
2. Weigh 0.0035 mole of sodium sulfate and place in another test tube
3. Add water to the test tube such that it is 1/3 full.
4. Agitate (shake or tap) each mix until the chemical inside it dissolves. You may want to
have your teacher show you an easy way to do this.
5. After both substances have completely dissolved pour the sodium sulfate solution into
the barium chloride solution.
6. Place the test tube in the centrifuge, making sure that another group’s (Or another test
tube with roughly equal weight) test tube is directly across from your test tube and allow
the centrifuge to run for 1 minute SAFETY: Take care with the centrifuge: It spins at
a very high speed—keep fingers away from the spinning centrifuge—it can take
your finger OFF!!
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. CAUTION 2:
Do not add cold water to a hot crucible: It will crack!!
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)
Mass of oxygen
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: Video can we watched at
http://learner.org Search for the series World of Chemistry and look for episode 11.
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
WS 3.1 The Mole
1. Describe/relate the size of the mole to an everyday object.
2. What is Avogadro’s Number?
3. How many marbles are in a mole of marbles?
4. How many mosquitoes are in a mole of mosquitoes?
WS 3.2 Molar Mass
Find the molar mass of the following compounds: Show work and include units
1. CO2
9. Lead IV Sulfite
2. Fe2O3
10. Lead IV Sulfide
3. AgCl
11. Lead II sulfate
4. Ca3(PO4)2
12. Lead II Sulfite
5. W3(PO3)5
13. Lead II Sulfide
6. Fe(C2H3O2)2
14. Copper I Sulfide
7. Calcium Carbonate
15. Copper II Sulfite
8. Lead IV Sulfate
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
WS 3.3: Mole Conversions (one step)
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. How many atoms are in 1.5 moles of neon?
2. How many moles of SF6 are there in 4,595,000,000,000,000,000 molecules of
SF6?
3. Calculate the number of moles in 5.45x1025 atoms of Zn
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. Calculate the number of grams in 3.25-mol of AgNO3
5. What is the volume of 0.38 moles of any gas at STP?
6. Calculate the number of moles in 32.2-L of NH3
7. What is the mass of 51 liters of oxygen gas?
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
WS 3.4: Mole Conversions (two steps)
Directions: Answer the following questions. Set-up all problems using the factor-label
method of dimensional analysis and show all your work and units.
8. What volume would be occupied by 9.45 x 1024 molecules of CO2 gas at STP?
9. How many calcium atoms would be in a 100 gram sample of calcium metal?
10. How many grams are in 5.6 x 1023 atoms of Zinc?
11. Calculate the number of molecules in 4.56-g of Pb(NO3)2
12. Calculate the number of liters in 3.25-g of NH3
13. Calculate the number of liters in 5.43x1025 molecules of H2
14. Calculate the number of grams in 3.54-L of CO2
15. Calculate the number of grams in 9.7x1022 molecules of CH3CH2OH
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WPHS Chemistry: Unit 3 Packet: The Mole
Name________________
WS 3.5 %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________________
WS 3.6: Empirical 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________________
WS 3.7 Molecular Formula
1. 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.
2. Determine the molecular formula for a compound that contains 94.1%
oxygen and 5.9% hydrogen and a molecular mass of 34 g/mol.
3. 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
4. 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________________
5. 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.
6. 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.
7. 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?
8. 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
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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
24
9.45x10 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
23
24
100g 1mol 6.02x10 atoms
x
x
 1.5x10 atoms
1
40g
1mol
14. How many grams are in 5.6 x 1023 atoms of Zinc? 60.g


4.595.6x10 23 molec
1mol
65g
x
x
 60.g
23
1
6.02x10 molec 1mol
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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

- 25 -
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%

- 26 -

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
- 27 -
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.
- 28 -
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

- 29 -
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.

- 30 -
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
- 32 -
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
- 33 -
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
- 34 -
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
- 35 -
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
- 36 -
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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- 37 -