Sophomore Chemistry
Unit 08 – Moles
Unit 08 – Moles
Page 1
NAME: __________________________
You are undoubtedly familiar with the word dozen. A dozen is a grouping of twelve things. It can mean twelve donuts.
It can mean twelve eggs. It can mean twelve cars. The identity of the objects being counted is not as important as the
fact that there are twelve of them. In short, dozen is a word that means a number.
In chemistry, the items we count are much smaller than donuts, eggs or cars. Atoms, molecules, and ions, are
infinitesimal in size, and to measure out a significant amount of them, we need way more than twelve. Instead of a
dozen, we will be using the mole, which is a grouping of 602,000,000,000,000,000,000,000 or 6.02 × 1023 objects. We
can then convert between the number of molecules (or atoms), the number of moles, the mass of the molecules, and
the volume of the molecules. Typically, the chart found in most textbooks looks something like this.
When I was in high school, learning this for the first time, my teacher likened this conversion chart to a map, and called
it Mole Island. And you could travel from Mole Island to Volume Island, or Mass Island, and it was pretty lame and
stupid. And I thought to myself, “There’s got to be a better way to do this, or at least a way that isn’t so lame and
stupid.” And after fourteen years of teaching, and seeing other people doing it the same way, using the same analogy, I
can confidently tell you that there is no better way. The only option left is to embrace the lame and stupid, and try to
have a little fun with it. So without further ado…
Sophomore Chemistry
Unit 08 – Moles
Page 2
Welcome to
the Mole
Archipelago
!
Come for the fun!
Stay for the conversions!
Sophomore Chemistry
Unit 08 – Moles
Page 3
Welcome to the Mole Archipelago, the Bermuda Triangle’s
premier tourist destination since 1811. The Mole
Archipelago is a chain of islands located in the dangerous,
shark-infested waters of the Bermuda Triangle. It was
discovered by Italian explorer Amedeo Avogadro in 1811,
when he was searching for the Fountain of Youth.
Avogadro was sailing east of Miami when he discovered
Liter Island. While continuing to explore, he found a
narrow, shark-free channel that led directly to Mole Island. Further
exploration led to the discovery of other islands, including Particle Island,
Gram Island, Mystery Island, the Molarity Atoll, and Baboon Reef.
NAME: __________________________
READING ASSIGNMENT: Read and take notes on pages 115-116 in your textbook.
In the space provided, outline the important points made in the assigned text.
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Solve the following conversion problems. Show your work.
1 dozen apples = 2.0 kg apples = 0.20 bushel apples
I have 12.5 kg of apples. How many apples is that?
Sophomore Chemistry
Unit 08 – Moles
Page 4
What is the mass of 0.50 bushel of apples?
Assume that a variety of apples has 8 seeds in each apple. How many seeds are in 14 kg of apples?
The first stop you should make in the Mole Archipelago is scenic and lovely
Particle Island. Upon meeting the natives of Particle Island, you will
probably notice two things. First, they are all very friendly, and often greet
visitors with a smile and a hug. Second, they are strangely obsessed with
counting things.
Oddly enough, Particle Islanders often take breaks from whatever they are
doing in order to count whatever they see in front of them. They count
people, trees, and the birds in the sky. Local legend has it that the chief of
the Particle Island tribe once counted 602,000,000,000,000,000,000,000
grains of sand in one sitting. That’s a whole lot of sand!
Particle Island:
1 mole X = 6.02×1023 atoms/molecules X
READING ASSIGNMENT: Read and take notes on pages 116-119 in your textbook.
In the space provided, outline the important points made in the assigned text.
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Sophomore Chemistry
Unit 08 – Moles
Page 5
Solve the following conversion problems. Show your work.
How many moles is 2.80 × 1024 atoms of Silicon?
How many molecules is 0.360 moles of water?
How many total atoms are there in 1.14 moles of SO3?
NAME: __________________________
How many moles are there in 4.65 × 1024 molecules of NO2?
How many molecules are there in 45.6 moles of CH4?
How many total atoms are there in 1.03 moles of NH3?
How many moles are made from 7.83 × 1024 molecules Ethanol?
How many moles are made from 1 atom of hydrogen?
READING ASSIGNMENT: Read and take notes on pages 119-125 in your textbook.
Sophomore Chemistry
Unit 08 – Moles
Page 6
In the space provided, outline the important points made in the assigned text.
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___________________
Do you need to shed some unsightly pounds? Gram Island is home to one of the world’s premier
live-in fitness resorts. While on Gram Island, you will see the residents working out and eating
right. You might spot health enthusiasts periodically doing calculations while consulting a table
of allowed foods, in order to make sure they are not consuming too many calories.
Gram Island:
1 mole X = MM g X
Answer the following questions. Show work when necessary.
What has more mass, an egg or a car? ____________________
Why? What is mass? ________________________________________________________________________________
__________________________________________________________________________________________________
What has more mass, a dozen eggs, or a dozen cars? ____________________
Why? Explain your answer: ___________________________________________________________________________
__________________________________________________________________________________________________
__________________________________________________________________________________________________
Distinguish between gram atomic mass, gram molecular mass, and gram formula mass. Refer to your textbook if these
terms are still a bit confusing:
Gram Atomic Mass: ___________________________________________________________________________
Gram Molecular Mass: ________________________________________________________________________
Gram Formula Mass: __________________________________________________________________________
Sophomore Chemistry
Unit 08 – Moles
Page 7
Find the molar mass of each of the following compounds. You many round mass numbers from the periodic table to the
nearest whole number. Show your work.
CO2: 12 + 16 + 16 = 44 g/mol
H2:
Au:
HCl:
H2O:
H2SO4:
H2C2O4:
NaCl:
SCl6:
CaCl2:
N2O5:
Mg3N2:
P4O10:
Al2(SO4)3∙5H2O:
NaSO4:
Ca(OH)2:
Ba(C2H3O2)2:
Zn3(PO4)2:
O3:
Na3PO4:
VCl3:
NAME: __________________________
To further illustrate the concept of molar mass, your teacher will pass around some plastic bags that each contain one
mole of a substance. Different substances have different molar masses. Make sure to make some observations about
the molar mass bags in the space provided.
Perform the following conversions. Show all work.
56 grams of CO2 into moles
1060 g C6H6 into moles
1.24×103 g Au2(SO4)3 into moles
60 g O2 into moles
81.5 g NH3 into moles
Sophomore Chemistry
Unit 08 – Moles
Page 8
75 g Au into moles
0.014 moles of Mg3N2 into grams
80 moles of P4O10 into grams
READING ASSIGNMENT: Read and take notes on pages 126-127 in your textbook.
In the space provided, outline the important points made in the assigned text.
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The residents of Liter Island are hot-air balloon enthusiasts, and as
far as they are concerned, the bigger, the better! On Liter Island, you
can enjoy one of the daily balloon races as a spectator, or if you are
feeling particularly daring, as a participant.
Also while on the island, be sure to check out the birthplace of rock
and roll legend Scott Weiland. Tours run daily beginning at 9AM.
Liter Island:
1 mole X = 22.4 L X
Sophomore Chemistry
Unit 08 – Moles
Page 9
Answer the following questions. Show all work.
What is the volume at STP of 3.20 × 10-3 mol of CO2?
What is the volume at STP of 0.960 mol of CH4?
What is the volume at STP of 3.70 mol of N2?
NAME: __________________________
How many moles are in 67.2 L SO2 at STP?
How many moles are in 0.880 L He at STP?
How many moles are in 1.00 × 103 L C2H6 at STP?
Density = mass ÷ volume
Density of a gas = mass of 1 mole (molar mass from periodic table) ÷ volume of 1 mole (22.4 L)
A gaseous compound composed of sulfur and oxygen that is linked to the formation of acid rain has a density of 3.58
g/L at STP. What is the molar mass of this gas? What do you think the identity of the gas is? Explain.
Sophomore Chemistry
Unit 08 – Moles
What is the density of krypton gas at STP?
What is the density of xenon gas at STP? Is it more or less dense than helium?
What does STP mean? Why is it important to include it when talking about a sample of gas?
Page 10
Sophomore Chemistry
Unit 08 – Moles
Page 11
Molar Volume Laboratory Activity
Just as a “dozen” is a grouping of 12 objects, a “mole” is a grouping of 6.02×1023, or 602,000,000,000,000,000,000,000
objects. Normally, we only use the mole when dealing in incredibly small particles, like atoms or molecules, and one
mole of a chemical sample doesn’t usually take up that much space. Today, however… well, you’ll see.
A new element, Splitpeaium, was discovered on a recent trip to the grocery store. The element has the largest atoms
ever discovered, so large in fact, that they are about the size of split peas (and coincidentally, the same color). Your job
is to determine the volume that would be occupied by 1 mole of split peas, er, Splitpeaium atoms.
To perform this lab, you are to use only a sample of Splitpeaium atoms and a graduated cylinder. Any other
instruments, materials, and chemicals are absolutely prohibited. Minimal contact with water causes Splitpeaium to
become extremely volatile. DO NOT use water under any circumstances!!
You must write your own procedure for this laboratory exercise. If you have any doubts as to how to proceed, refer
back to the laboratory question:
“What is the volume of 6.02×1023 atoms of Splitpeaium?”
Students are required to perform at least five trials and put all data in a ruled table. Show all work in the space provided
below.
Use the internet or other research to find something that is the same size as one mole of Splitpeaium atoms. What did
you find?
Sophomore Chemistry
Unit 08 – Moles
Page 12
NAME: __________________________
READING ASSIGNMENT: Read and take notes on pages 128-130 in your textbook.
In the space provided, outline the important points made in the assigned text.
___________________________________________________________________________________________
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Perform the following multiple-step conversions. Show work.
Convert 56.2 g CO2 into liters of CO2 gas at STP.
Convert 7.62 × 1023 molecules of N2O5 into grams of N2O5.
Convert 65.3 L P4O10 into molecules of P4O10.
Convert 124 g Au(ClO4)3 into molecules of Au(ClO4)3.
Convert 45.2 L (NH4)3PO4 into grams of (NH4)3PO4.
Sophomore Chemistry
Unit 08 – Moles
Page 13
As mentioned on page 1 of this packet, a conversion chart like the one that follows can be useful for solving multiple
step conversions. Use this chart to help you solve the problems on this and the preceding page.
Convert 112.7 g H2O2 into L H2O2 at STP.
Convert 46.8 L SO3 gas into molecules SO3.
OVERTIME CREDIT OPPORTUNITY: Mole Conversion Concentration Card Game – ask your teacher for details.
Sophomore Chemistry
Unit 08 – Moles
Page 14
NAME: __________________________
Mystery Island is home to Mole Archipelago’s world famous automobile factory. The residents who work there have an
intense fascination with the construction of cars, and will often be overheard repeating the relationships of parts that go
into a Molemobile.
“Four wheels equals one molemobile.”
“One molemobile equals two side-view mirrors.”
“One engine equals one molemobile.”
“One molemobile equals two axles.”
Upon visiting Mystery Island, many visitors find that the experience changes them in a permanent way.
Mystery Island:
1 mole X = ? mole Y
The Mystery Island concept is not found in your textbook. In the space provided, outline the important points made in
the lecture regarding Mystery Island.
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You will probably find the following chart useful as you approach problems in which the formula of the compound you
are looking at changes. Use it as you solve the problems on the next page. Show all work.
6.02 × 1023
atoms or
molecules X
22.4 L X
MM g X
from
Periodic
Table
6.02 × 1023
atoms or
molecules Y
1 mole X
1 mole Y
22.4 L Y
MM g Y
from
Periodic
Table
Sophomore Chemistry
150 g H2SO4 into molecules of H2SO4.
42 L NH3 gas into molecules of NH3.
82.5 g P4O10 into molecules of P4O10.
47.3 g P2O5 into atoms of O.
1.23×1024 molecules of H2O into g H.
78 L O2 into g O.
1000 atoms of Au into g Au.
53.2 g H3PO4 into atoms of O.
63 g Na2SO4 into atoms of Na.
Unit 08 – Moles
Page 15
Sophomore Chemistry
Unit 08 – Moles
Page 16
NAME: __________________________
Laboratory Activity – Counting Atoms
Chalk is a soft, white, porous form of limestone composed of the mineral calcite. It is also a sedimentary rock. It is
relatively resistant to erosion compared to clay and dirt, causing it to form steep cliffs where chalk ridges meet the sea.
Chalk is formed in shallow waters by the gradual accumulation of the calcite mineral remains of micro-organisms over
millions of years. It has been mined from quarries since before recorded history, and has been used as building
materials and in agriculture.
Chalk is also used for drawing on rough surfaces, as it readily crumbles, leaving particles that stick loosely to these
surfaces. Blackboard chalk is currently made from the mineral gypsum (calcium sulfate, CaSO4).
In this laboratory investigation, you will use your knowledge of molar conversions to determine the number of oxygen
atoms that are transferred to the chalkboard in an ordinary classroom situation. In short:
“Find the number of atoms of oxygen that are stuck to the board when you write your name in chalk.”
Procedure:
1. Obtain a piece of chalk from the instructor.
2. Use the analytical balance to find the mass of the piece of chalk before writing your name.
3. Use the chalk to write your name on the board.
4. Use the analytical balance to find the mass of the piece of chalk after writing your name.
5. Subtract the “after” mass from the “before” mass to determine the mass of the chalk that was stuck to the board.
6. Use molar conversions to convert grams of chalk (CaSO4) to atoms of oxygen. Show your work in the space below.
mass of chalk before
writing your name
g
mass of chalk after
writing your name
g
mass of chalk used in
writing your name
g
Sophomore Chemistry
Unit 08 – Moles
Page 17
Perform the following multi-step conversions. Show all work.
6.150 g H2S into atoms of H.
1.42×1031 molecules P4O10 into grams of P.
0.44 g O3 into atoms of O.
943.38 L O2 into g O.
0.55 g H3PO3 into atoms of H.
READING ASSIGNMENT: Read and take notes on pages 131-133 in your textbook.
In the space provided, outline the important points made in the assigned text.
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Sophomore Chemistry
Unit 08 – Moles
Page 18
NAME: __________________________
The relative amounts of each element in a compound are expressed as the percent composition, or the percent by mass
of each element in a compound. The percent composition of a compound has as many percent values as there are
different elements in a compound. The percents must total 100%
The percent by mass of an element in a compound is the number of grams of the element divided by the number of
grams in the compound, multiplied by 100%.
% mass of element A
=
grams of element A
----------------------------grams of compound
× 100%
To calculate the percent composition of a known compound, use the chemical formula to calculate the molar mass. This
gives the mass of one mole of the compound. Then, for each element, calculate the percent by mass in one mole of the
compound. This is done by dividing the mass of each element in one mole of the compound by the molar mass and
multiplying the result by 100%. Remember that the subscripts in the formula of the compound are used to calculate the
grams of each particular element in a mole of that compound.
% mass
=
grams of element in 1 mole of compound
-------------------------------------------------molar mass of compound
× 100%
Consider the compound potassium permanganate, KMnO4. It is composed of three elements, K, Mn, and O. One mole
of KMnO4 contains one mole of K (atomic mass = 39), one mole of Mn (atomic mass = 55), and four moles of O (atomic
mass = 16 × 4 = 64). By adding the masses of each of these elements, we find that the molar mass of KMnO4 is 158
grams per mole. To find the percent composition of the compound, we just use the equation from above, with specific
numbers for each element.
% mass K
% mass Mn
% mass O
=
39 grams K
-----------------------158 grams KMnO4
× 100%
=
24.7% K
=
55 grams Mn
-----------------------158 grams KMnO4
× 100%
=
34.8% Mn
=
64 grams O
-----------------------158 grams KMnO4
× 100%
=
40.5% O
We can double check this result by making sure that all of the percentages add to 100%.
24.7 + 34.8 + 40.5 = 100%
Sophomore Chemistry
Unit 08 – Moles
Page 19
Answer the following questions. Show all work.
Find the percent composition of each of the following compounds.
a. NaHSO4
b. (NH4)2SO4
c. C12H22O11
d. K2Cr2O7
In the laboratory, 9.03 g Mg combines completely with 3.48 g N to form a compound. What is the percent composition
of this compound?
When a 14.2 g sample of mercury (II) oxide is decomposed into its elements by heating, 13.2 g Hg is obtained. What is
the percent composition of this compound?
Calculate the percent oxygen in iron (III) sulfate.
Sophomore Chemistry
Unit 08 – Moles
Page 20
NAME: __________________________
Laboratory Experiment – Water Marbles
Water Marbles™ are little beads made of a super-absorbant polymer. The tiny plastic beads absorb an incredible
amount of water, and grow to form large spheres that have the same index of refraction as water (they are invisible
when immersed in water). They are used for gardening, and are often found in table decorations. We are going to find
out how much water they absorb, and in doing so, the percent composition of the water marbles.
1.
2.
3.
4.
5.
6.
7.
Obtain a water marble from your instructor.
Find the mass of the water marble. This is the mass of the super-absorbant polymer, and will not change.
Obtain a small, labeled cup, and fill it with water.
Immerse the water marble in the water.
After one day has passed, remove the water marble from the cup, and find the mass of the marble.
Return the water marble to your instructor.
Find the Percent Composition of polymer and water in the saturated water marble.
Mass of polymer
Mass of polymer + water
Mass of water
Find the percent composition of each of the following compounds. Show all work.
Fe3(PO4)2
H2CO3
C6H14
% Composition Breakdown
Sophomore Chemistry
Unit 08 – Moles
Page 21
READING ASSIGNMENT: Read and take notes on pages 133-136 in your textbook.
In the space provided, outline the important points made in the assigned text.
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The empirical formula is the lowest whole-number ratio of elements in a compound. The molecular formula is also a
ratio of elements in a compound, but is not necessarily the simplest whole-number ratio. Use the following steps to find
the empirical or molecular formula of a compound:
1.
2.
3.
4.
5.
6.
Find the percentages of all elements in the compound.
Convert percentages to grams.
Convert grams of each element to moles of each element.
Divide all numbers of moles by the smallest number.
Multiply or round to get the empirical formula.
Use the molecular mass to find the molecular formula.
EXAMPLE: A compound composed of carbon, hydrogen, nitrogen, and oxygen has a molecular mass of 174 g/mole.
27.59% of the compound by mass is carbon. 1.15% is hydrogen. 16.09% is nitrogen. The rest of the
compound is oxygen. Find the molecular formula of the compound.
ANSWER: We will follow the steps above. The resolution of each step is typed in bold faced print.
Step 1 – Find the percentages of all elements in the compound. The percentage of oxygen is unknown. Because all
percentages should add up to 100%, the percentage of oxygen can be found by subtracting the other percentages from
100%. The percentage of oxygen is 100 − 27.59 − 1.15 − 16.09 = 55.17% oxygen.
Step 2 – Convert percentages to grams. The problem does not specify the size of the sample in question. Therefore, we
can assume that a 100 gram sample is being used. Because 27.59% of the sample is carbon, and we are assuming that
we have 100 grams of the sample, 27.59 grams of the sample is carbon. If we have a 100 gram sample, we have 27.59 g
C, 1.15 g H, 16.09 g N, and 55.17 g O.
Sophomore Chemistry
Unit 08 – Moles
Page 22
NAME: __________________________
Step 3 – Convert grams to moles. To accomplish this, we use the mole conversions learned earlier in this unit. The
molar mass of each element can be found in the periodic table.
27.59 g C
-----------1
×
1 mole C
-----------12 g C
= 2.299166667 moles C
Repeating this calculation for each of the elements, we find that we have
2.299166667 moles C, 1.15 moles H, 1.149285714 moles N, and
3.448125 moles O.
Don’t round any numbers off just yet.
Step 4 – Divide all numbers by the smallest number. Of these four values, the smallest is 1.149285714. Therefore:
For Carbon:
For Hydrogen:
For Nitrogen:
For Oxygen:
2.299166667
---------------- = 2.0005
1.149285714
1.15
---------------- = 1.0006
1.149285714
1.149285714
---------------- = 1.0000
1.149285714
3.448125
---------------- = 3.0002
1.149285714
Step 5 – Multiply or round to get the empirical formula. All four of these numbers are close enough to whole numbers
to be rounded off. Rather than C2.0005H1.0006N1.0000O3.0002, we can write the empirical formula as C2HNO3.
Step 6 – Use the molecular mass to find the molecular formula. The problem states that the molecular mass of the
compound is 174 g/mole. The empirical formula C2HNO3 has a mass of 87 g/mole. 174 g/mole is exactly twice as large
as 87 g/mole. Therefore, to get the molecular formula, we double the empirical formula, getting C4H2N2O6.
Use the method described above to find empirical formulas for compounds with the following compositions:
25.9% nitrogen, 74.1% oxygen
94.1% oxygen, 5.9% hydrogen
Sophomore Chemistry
79.8% C, 20.2% H
67.6% Hg, 10.8% S, 21.6% O
27.59% C, 1.15% H, 16.09% N, 55.17% O
62.1% C, 13.8% H, remainder is N
81.8% C, 18.2% H
Unit 08 – Moles
Page 23
Sophomore Chemistry
Unit 08 – Moles
Page 24
NAME: __________________________
Laboratory Activity – Formula of a Hydrate
Many salts that have been crystallized from a water solution appear to be dry, but when they are heated, large amounts
of water are given off. The crystals often change color when the water is released. This suggests that water is a part of
their crystal structure. These compounds are called hydrates, meaning that they contain water. When these
compounds are heated strongly in a crucible, the water is driven off, leaving an anhydrous compound (without water).
Usually, the amount of water present in a compound is a whole-number mole ratio. The formula of a hydrate is written
with a dot between the formula of the salt and water, as in the example: MgSO4∙2H2O. In this example, the formula of
the anhydrous salt is simply MgSO4. The formula of this hydrate indicates that two moles of water are combined with
one mole of the magnesium sulfate.
In this experiment, you will be given a sample of copper (II) sulfate hydrate and asked to find the percent of water in the
hydrate. The formula is CuSO4∙XH2O. Using logic and some calculations, you should be able to find the value of X.
Remember, this formula is a ratio of moles, and not grams. Show your work in the blank space below. Find the formula
and box your answer.
1.
2.
3.
4.
5.
6.
7.
Put on goggles.
Obtain a crucible and cover.
Using the balance, find the mass of the empty crucible.
Fill the crucible halfway with the hydrate (blue).
Find the mass of the crucible and hydrate.
Using subtraction, find the mass of the hydrate.
Place the crucible in a pipestem triangle on an iron ring above a Bunsen burner. Place the cover on top of the
crucible so that a small opening exists, allowing any water that is driven off to escape into the air.
FROM THIS POINT ON, YOU MUST NOT TOUCH THE CRUCIBLE WITH YOUR BARE HANDS!!
8. Use the burner to heat the crucible for five minutes, driving off the water from the hydrate, leaving only the
anhydrous salt (white).
9. Turn the burner off and place the crucible on the iron ring stand for cooling. Do not set the crucible on the
countertop.
10. Let the crucible cool for five minutes.
11. Find the mass of the crucible and anhydrous salt.
12. Using subtraction, find the mass of the anhydrous salt.
13. Add a few drops of water to the anhydrous salt. Observe what happens.
14. Clean up your station, and return all supplies to where they belong.
Sophomore Chemistry
Unit 08 – Moles
Page 25
Answer the following. Show work whenever appropriate.
Calculate the percent composition of the compounds that are formed when 222.6 g N combines completely with
77.4 g O.
The compound methyl butanoate smells like apples. Its percent composition is 58.8% C, 9.8% H, and 31.4% O.
Methyl butanoate’s molar mass is 102 g/mol. What is its molecular formula?
Calculate the percent composition of calcium acetate, Ca(C2H3O2)2.
Using the results of the previous problem, calculate the amount of hydrogen in 124 g calcium acetate.
Which of the following molecular formulas are also empirical formulas? Circle any that apply.
a.
b.
c.
d.
C5H10O5
C6H12O2
C55H72MgN4O5
C12H17ON
Sophomore Chemistry
Unit 08 – Moles
Page 26
NAME: __________________________
Answer the following. Show work whenever necessary.
A compound contains 44% Phosphorus and 56% Oxygen by mass, and a molecular mass of 284 g/mol. Find the
molecular formula of the compound.
An organic compound contains 88.89% Carbon and 11.11% Hydrogen by mass. The molecular mass of the organic
compound is 54 g/mol. Find the molecular formula of the compound.
A compound containing only Calcium, Carbon, and Oxygen, was mined in the Rocky Mountains. 39.95% of the
compound is Calcium. By mass, there is four times as much Oxygen as there is Carbon. Find the empirical formula.
Iron forms an ionic compound with hydroxide (OH-1). 52% of the compound by mass is Iron. Find the charge on the
iron ion by finding the empirical formula.
Sophomore Chemistry
Unit 08 – Moles
Page 27
Answer the following. Show work as appropriate.
Analysis of a compound shows that it contains 10.88 g of calcium and 19.07 g of chlorine. Determine the empirical
formula of this compound.
Determine the empirical formula of a compound that contains 69.5% oxygen and 30.5% nitrogen.
READING ASSIGNMENT: Read and take notes on pages 377-380 in your textbook.
In the space provided, outline the important points made in the assigned text.
___________________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
___________________________________________________________________________________________
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Sophomore Chemistry
Unit 08 – Moles
Page 28
NAME: __________________________
The natives who live on the Molarity Atoll are world-famous for their sense
of taste, especially when it comes to their primary export, the powdered
drink-mix known as Mole-Aid.
Residents of the Molarity Atoll have taste buds that are so sensitive, they
can detect slight differences between any two samples of Mole-Aid. They
are experts, of course, at diluting the Mole-Aid to their liking.
Visit the Mole-Aid factory on weekdays between 9AM and 5PM. There is a
tour, a complimentary tasting of new Mole-Aid flavors, and children can get
their picture taken with the official mascot of the tasty beverage, Mole-Aid
Man.
Molarity Atoll:
Molarity = Moles of solute ÷ Liters of solution
Dilution Equation:
M1 × V1 = M2 × V2
A solution is made when solute dissolves into solvent. The solute is the
substance (usually a solid) that is poured, mixed, or stirred into the solvent
(usually a liquid).
The concentration of a solution is a measure of the amount of solute that is
dissolved in a given quantity of solvent. A dilute solution is one that
contains only a low concentration of solute. By contrast, a concentrated
solution contains a high concentration of solute.
The most important unit of concentration in chemistry is molarity.
Molarity (M) is the number of moles of solute dissolved per liter of
solution. Molarity is also known as molar concentration and when
accompanying a numerical value is read as “molar.” Note that the volume
involved is the total volume of the resulting solution, and not the volume of the solvent alone.
To determine the molarity of any solution, calculate the number of moles in 1 L
of the solution, using the following equation:
Molarity (M)
=
moles of solute
--------------------liters of solution
Solutions of certain standard molarities are usually available in the laboratory.
However, you may need a dilute solution of a different concentration. You can
make a solution less concentrated by diluting it with solvent.
Sophomore Chemistry
Unit 08 – Moles
Page 29
The dilution reduces the moles of solute per unit volume; however, the total moles of solute in solution does not
change. Thus:
Moles of solute before dilution = moles of solute after dilution
Rearranging the definition of molarity gives an expression for moles of solute in terms of molarity and volume:
Moles of solute = Molarity (M) × liters of solution (V)
The total number of moles of solute remains unchanged upon dilution, so you can write:
Moles of solute
=
M1 × V1
=
M2 × V2
where M1 and V1 are the initial solution’s molarity and volume, and M2 and V2 are the final solution’s molarity and
volume. Volumes can be in liters or milliliters, as long as the same units are used for both V1 and V2.
Through the application of a bit of logic, we can determine that the quantity (V2 − V1) is equal to the volume of solvent
added to make the dilution.
Solve the following problems. Show all work.
6.150 g CaCl2 is used to make 1.2 L of solution. Calculate the molarity of the solution.
3.13 g NaNO3 is used to make a 1.05 M solution. How many milliliters of solution were made?
A 3.1 L of a 10.65 M solution of N2O5 is used in an experiment. How many grams of N2O5 is that?
50 mL of a 1.42 M solution of H3PO4 is diluted to 175 mL total volume. What is the concentration of the dilute
solution?
Sophomore Chemistry
Unit 08 – Moles
Page 30
NAME: __________________________
How much water must be added to 50 mL of a 1.30 M solution in order to make a 0.23 M solution?
30.44 mL of water is added to 70.15 mL of a 2.5 M solution of an acid. What is the concentration of the dilute
solution?
How many mL of a 2 M solution of Acid is needed to make 750 mL of a 0.5 M solution?
How many grams of Na2SO4 must be added to 3.04 L of water to make a 1.25 M solution?
If 65.3 grams of Au(NO3)3 is used to make 57 mL of solution, find the molarity?
How many milliliters of water are required to dilute 45 mL of 1.3 M HCl to 0.75 M?
What is the molarity of a solution if 403.4 grams of K3PO4 are needed to make 1.35 L?
Sophomore Chemistry
Unit 08 – Moles
Page 31
Design a Laboratory Activity – Find the Number of Atoms in a Drop
There are many ways to approach a scientific problem in the laboratory. Throughout this school year, you have used
several different laboratory techniques to uncover or support the truths that you have learned about in class and in the
textbook. You have entered data in many different tables, and manipulated numbers with many different algebraic
equations. The time has come for you to use what you have learned to design and execute your own investigation of a
scientific principle. The time has come for you to do your first design lab.
A design lab is an experiment in which the teacher does not provide you with specific instructions or an easily-filled-in
data table. You will have to create your own procedure and select your own data collection and analysis techniques.
Sometimes, you will be told what equipment is available; oftentimes, you will not. You will have to choose what you are
studying, how you will study it, and how you will present your findings.
Performing your first design lab can seem like a daunting task. Here are some tips that will help you organize a
successful design lab:
1. Select only one variable to study at a time. In conducting a planning lab, you should essentially be performing the
same experiment over and over, changing a single variable at a time. Every other variable except the one you are
observing must be isolated and controlled, if possible (or at least recorded if not possible). This might make your
experiment a little bit tedious, but it will insure more useful results.
2. Use an experimental setup that you are familiar with. When performing a planning lab, most of your time should
be spent collecting data, not fussing with a new apparatus that you don’t know how to use. If possible, you should
try to do the lab with an experimental setup that you have already used before. Refer back to old experiments for
help in putting together your procedure and apparatus. Consider how a very user friendly experiment you did
months ago can be reworked into answering a more advanced laboratory question now.
3. If possible, know what the outcome should be before the experiment begins. A little bit of research in the
textbook or on the internet should help you to craft a better hypothesis and create a more usable procedure. You
should not be afraid of any surprises that occur during data collection, but you should still try to avoid them
whenever possible.
4. Know your equipment before writing the procedure. Spend a little extra time to come in and investigate the types
of glassware and equipment that is at your disposal for a planning lab. You should select the right tool for the right
job. If you are reacting 5 mL of acid with a small amount of metal, a small test tube is a more appropriate container
than a 1000 mL beaker. You will get better results if you use the right equipment.
Students are working on this experiment in groups of two. As you and your partner plan the experimental approach,
make sure to consider the following questions:
What is the identity of the liquid chemical that will be used?
What delivery system will be used for measuring out a drop?
Are all drops the same size? If not, how can this variable be accounted for?
Fill in the blanks on the next four pages to complete your laboratory report.
Sophomore Chemistry
Unit 08 – Moles
Laboratory Report
Page 32
NAME: __________________________
WRITE YOUR NAME ON THIS LINE.
Date: ______________
WRITE THE DATE
Title:
________________________________________________________________________________
THE TITLE OF A LABORATORY EXPERIMENT IS AS SPECIFIC AS POSSIBLE. IT SHOULD DESCRIBE THE REACTION
TAKING PLACE, OR THE PRINCIPLE BEING STUDIED. SOMETIMES, A GENERAL TITLE IS PROVIDED AND YOU WILL
HAVE TO MAKE IT SPECIFIC. IN THIS CASE, YOU WILL HAVE TO CRAFT THE TITLE FROM SCRATCH.
Purpose:
_____________________________________________________________________________________
_____________________________________________________________________________________
THE PURPOSE SHOULD EXPLAIN THE POINT OF THE EXPERIMENT. IN THIS SECTION, YOU SHOULD RESTATE, IN YOUR OWN
WORDS, THE POINT OF THIS EXPERIMENT. YOU SHOULD INCLUDE MENTION OF ANY CONCEPTS THAT ARE BEING
DEMONSTRATED, AS WELL AS ANY TECHNIQUES THAT ARE BEING USED.
Hypothesis:
_____________________________________________________________________________________
_____________________________________________________________________________________
THE HYPOTHESIS IS AN EDUCATED GUESS AS TO WHAT IS GOING TO HAPPEN IN THE EXPERIMENT. IF POSSIBLE,
IT SHOULD BE A QUANTITATIVE ESTIMATE OF THE EXPECTED RESULTS.
Equation:
_____________________________________________________________________________________
WRITE A BALANCED CHEMICAL EQUATION FOR ANY REACTIONS THAT YOU ARE GOING TO CONDUCT IN THE EXPERIMENT.
Materials:
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
________________________________
THE MATERIALS SECTION IS A LIST OF ALL OF THE EQUIPMENT THAT YOU USE IN THE EXPERIMENT, AS WELL AS ANY
CHEMICALS YOU USE. IF POSSIBLE, THE SIZES AND QUANTITIES OF THE EQUIPMENT SHOULD BE LISTED.
Apparatus:
AN APPARATUS DRAWING IS A
VISUAL EXPLANATION OF HOW THE
EQUIPMENT FITS TOGETHER. MAKE
SURE TO INCLUDE LABELS FOR EACH
OF THE PARTS OF THE APPARATUS.
Sophomore Chemistry
Unit 08 – Moles
Page 33
Procedure:
1. _________________________________________________________________________________________
2. _________________________________________________________________________________________
3. _________________________________________________________________________________________
4. _________________________________________________________________________________________
5. _________________________________________________________________________________________
6. _________________________________________________________________________________________
7. _________________________________________________________________________________________
8. _________________________________________________________________________________________
9. _________________________________________________________________________________________
10. ________________________________________________________________________________________
11. ________________________________________________________________________________________
12. ________________________________________________________________________________________
13. ________________________________________________________________________________________
14. ________________________________________________________________________________________
15. ________________________________________________________________________________________
16. ________________________________________________________________________________________
17. ________________________________________________________________________________________
THE PROCEDURE IS A LIST OF SIMPLE, ONE-STEP COMMANDS THAT HAVE TO BE FOLLOWED TO COMPLETE THE EXPERIMENT.
Data Table:
THE DATA TABLE(S) SHOULD BE FORMATTED FOR EASY READING. BOTH QUANTITATIVE
AND QUALITATIVE DATA SHOULD ALWAYS BE RECORDED IN A LABORATORY REPORT
Sophomore Chemistry
Unit 08 – Moles
Page 34
NAME: __________________________
Calculations:
THE CALCULATIONS SHOULD INCLUDE ANY AND ALL DATA PROCESSING AND NUMBER CRUNCHING NECESSARY
TO COMPLETE THE LAB, NO MATTER WHEN IT OCCURRED IN THE LAB. SOME OF THE CALCULATIONS ABOVE
HAVE BEEN WRITTEN OUT FOR YOU. FOR THE PURPOSES OF A TYPED REPORT, TABLE FUNCTIONS IN MICROSOFT
WORD ARE RECOMMENDED. IF YOU DO NOT KNOW HOW TO USE TABLE FUNCTIONS, CONSULT YOUR TEACHER.
Conclusion:
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
THE CONCLUSION SHOULD STATE ANYTHING THAT WAS DISCOVERED DURING THE EXPERIMENT. IF POSSIBLE, DISCOVERIES
SHOULD BE BACKED UP WITH QUANTITATIVE AND QUALITATIVE EVIDENCE FROM THE DATA AND CALCULATIONS SECTIONS.
Sophomore Chemistry
Evaluation:
Unit 08 – Moles
Page 35
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
THE EVALUATION FOLLOWS THE CONCLUSION AND IDENTIFIES ANY FLAWS WITH THE PROCEDURE. THE CONDITIONS
OF THE LAB, LACK OF PERTINENT EQUIPMENT, FLAWS IN THE ACTUAL PROCEDURE SHOULD BE ANALYZED.
Suggestions:
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
THE SUGGESTIONS SECTION IS YOUR CHANCE TO DESCRIBE HOW THE EXPERIMENT MIGHT BE DONE DIFFERENTLY IN A
PERFECT WORLD. THINK ABOUT WHAT PROBLEMS YOU IDENTIFIED IN YOUR EVALUATIONS SECTION, AND COMMENT ON
THAT. A QUICK INTERNET SEARCH MIGHT FIND YOU A PROCEDURE OR APPARATUS THAT WASN’T READILY AVAILABLE IN
OUR LABORATORY SETTING.