Coyle/Tang-Johnson Chemistry Study Guide
TEST: Thursday 1/27/11
10.1 The Mole: Measurement of Matter
Define the following terms:
- mole
- Avogadro’s number
- representative particle
- molar mass
1. What kind of representative particles can one calculate using Avogadro’s number?
Converting Moles to # of Particles
 
Converting # of Particles to Moles
1 Mole = 6.02 x 10 23 particles therefore
1 mol
6.02 x 10 23 particles or
(particles particles.

moles)
If you are given
particles and want to find the moles you
divide by 6.02 x 10 23
6.02 x 10 23 particles
1 mol
(moles

particles)
If you are given
moles and you want to find particles then you multiply by 6.02 x 10 23 particles.
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Coyle/Tang-Johnson Chemistry Study Guide
If you want to find the # of atoms you first find the # of particles or molecules and then multiply by the # of atoms per molecule . (mol

particles

atoms)
Example: How many oxygen atoms are there in 5 moles of NO
3
?
1) Because NO
3
is a molecule, first find the number of particles of NO
3
in 5 moles.
5 mol NO
3
x 6.02 x 10 23 molecules NO
3
= 3.01 x 10 24 molecules NO
3
1 mol NO
3
2) Next, figure out how many oxygen atoms there are in NO
3
. There are 3 oxygen atoms in every molecule of NO
3
3) Now set up your equation:
3.01 x 10 24 molecules NO
3 x 3 oxygen atoms = 9.03 x 10 24 oxygen atoms
1 molecule NO
3
If you want, you can set it up as one big conversion rather than in 2 steps:
5 mol NO
3
x 6.02 x 10 23 molecules NO
3
x 3 atoms O = 9.03 x 10 24 atoms O
1 mol NO
3
1 molecule NO
3
PRACTICE:
2. How many molecules are there in 2.0 moles of FeSO
4
? _________
3. How many moles are in 7.5 x 10 19 molecules of ZnSO
4
? ________
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Coyle/Tang-Johnson Chemistry Study Guide
4. How many oxygen atoms are there 0.75 moles of CO
2
? _________
5. How many moles is 1.50 x 10 23 molecules of NH
3
?
6. How many atoms are in 1.75 mol CHCl
3
?
7. What is molar mass and from where do you find the information needed for this?
Find the molar mass of the following elements: a) K = ________ b) Ag = ________ c) Cl = _________
6. How would you find the molar mass of a compound like NaCl?
Find the molar mass of the following compounds: a) KCl = ________ b) H
2
CO
3
= ________ c) CaSO
4
= __________ d) Ca(NO
3
)
2
= ________
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Coyle/Tang-Johnson Chemistry Study Guide
10.2 Mole-Mass and Mole-Volume Relationships
Define the following terms:
- STP
- molar volume
Converting Moles to Mass
 
Converting Mass to Moles
1 Mole = molar mass of element or compound (in grams) therefore
1 mol
molar mass (g)
(mass

moles)
If you are given
mass and want to find the moles you
divide by the molar mass of the element or compound. or molar mass (g)
1 mol
(moles

mass)
If you are given moles and you want to find
mass then you
multiply by the molar mass of the element or compound.
Example 1: How many moles are in 53.2g of oxygen (O
2
)?
1) Find the molar mass of oxygen using the periodic table. Since there are 2 atoms of oxygen in O
2
, you must multiply 16 g oxygen by 2: 1 mol = 32 g oxygen
2) Use the conversion factor to set up your problem.
State the given first and multiply by the conversion factor so that the units cancel out on the bottom, and the unit you want it on top:
53.2g O x 1 mol O = 1.66 moles oxygen
32 g O
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Coyle/Tang-Johnson Chemistry Study Guide
Example 2: What is the mass of 12.3 moles of Al
2
O
3
?
1) Find the molar mass of Al
2
O
3
using the periodic table:
Al
2
= 27g x 2 = 54g
O
3
= 16g x 3 = 48g
Mass Al
2
O
3
= 102g so 1 mol = 102g Al
2
O
3
2) Use the conversion factor to set up your problem.
12.3 mol Al
2
O
3 x 102g Al
2
O
3
= 1,254.6g Al
2
O
3
1 mol Al
2
O
3
PRACTICE:
1. How many moles are there in 25.0g of NaCl? __________
2. How many moles are there in 100.0g of KMnO
4
? __________
3. How many grams are in 0.25 moles of KCl? __________
4. How many grams are in 0.50 moles of H
2
SO
4
? _________
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Coyle/Tang-Johnson Chemistry Study Guide
Converting Moles to Volume
 
Converting Volume to Moles
1 Mole = 22.4L of gas at STP therefore
1 mol
22.4 L gas at STP
(volume

moles)
If you are given
volume and want to find the moles you
divide by the 22.4 L. or 22.4 L gas at STP
(moles

volume)
If you are given moles and you want to find
volume then you
multiply by 22.4 L.
PRACTICE:
5. What is the volume of 0.60 moles of SO
2
gas at STP?
1 mol
6. What is the volume of 3.20 x 10 3 mol CO
2 at STP?
7. How many moles are in of 13.70 L of N
2 at STP?
8. At STP, how many moles are in of 1.25 L of He?
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Coyle/Tang-Johnson Chemistry Study Guide
Density = mass therefore Density of gas at STP = molar mass (g)
volume 22.4 L
Example: What is the mass of a compound found to be 1.964g/L at STP?
1) Plug in your given into the formula:
Density = molar mass (g)
22.4 L
1.964g/L = molar mass (g)
22.4 L
2) Solve for the mass by multiplying both sides by 22.4L
(1.964g/L) (22.4L) = 44.0g
PRACTICE:
9. What is the mass of a gas found to be 3.58g/L at STP?
10. What is the density of krypton gas at STP?
11. What is the mass of a gas found to be 62.3g/L at STP?
12. What is the density of CO2 gas at STP?
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Coyle/Tang-Johnson Chemistry Study Guide
STEPS FOR SOLVING MOLE PROBLEMS (always go to the MOLE first)
1) What is given?
2) What is the unknown?
3) Is it a 1-step or 2-step problem? a.
1-step = mol

molar mass
mol

particles
mol

volume b.
2-step = molar mass

particles
molar mass

volume
particles

volume
4)
If it’s a 1-step problem, write the given and solve using the conversion factor.
5) If it’s a 2-step problem, write the given, solve for the mol, then solve for the unknown.
Use the following MOLE ROAD MAP to help you solve mole problems:
*** PRACTICE THE PROBLEMS ON CLASS HANDOUTS ***
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Coyle/Tang-Johnson Chemistry Study Guide
10.3 Percent Composition and Chemical Formulas
Define the following terms:
- percent composition
- empirical formula
1. What formula can you use to find the percent composition from mass data?
2. What formula can you use to find the percent composition from a chemical formula?
PRACTICE:
3. A 13.60g sample of a compound made up of magnesium and oxygen has 5.40g of oxygen. What is the percent composition of this compound?
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Coyle/Tang-Johnson Chemistry Study Guide
4. A compound is formed when 9.03g Mg combines completely with 3.48g N.
What is the percent composition of the compound?
5. A 14.2g sample of mercury (II) oxide has 13.2g of Hg. What is the percent composition of this compound?
HYDRATES: To find the percent of water in a hydrate use the following equation:
% water = mass of water x 100
mass of the entire hydrate
(including the water)
6. What percentage of water is found in CuSO
4

5H
2
O?
7. A 2.5g sample of a hydrate of Ca(NO
3
)
2
was heated, and 1.7g of the anhydrous salt remained. What percentage of water was in the hydrate?
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Coyle/Tang-Johnson Chemistry Study Guide
EMPIRICAL FORMULAS
To find an empirical formula given percentage s:
1) Change each percentage into grams (notice all percentages add up to 100)
2) Convert grams to moles for each element
3) Divide each number of moles by the smaller number of moles to get the smallest whole-number ratio
4) If the ratio is not in whole-number form, multiply by the smallest number possible to get a whole-number ratio. These are the subscripts for the formula
Ex: A compound has 25.9% nitrogen and 74.1% oxygen. What is the empirical formula of the compound?
25.9% N

25.9g N x 1 mol N = 1.85 mol N
14 g N
74.1% O

74.1g O x 1mol O = 4.63 mol O
1.85
16 g O
1.85 mol N = 1 mol N ; 4.63 mol O = 2.5 mol O
1.85
To find an empirical formula given mas s:
Since 1:2.5 is not a whole-number ratio, multiply by 2 to get whole numbers:
1 mol N x 2 = 2 mol N
2.5 mol O x 2 = 5 mol O
Empirical formula = N
2
O
5
1) Follow steps 2-4 in procedure to find the empirical formula given percentage
PRACTICE:
8. When iron oxide Fe
2
O
3
reacts with 18.94g of aluminum metal, iron is produced along with 35.74g of aluminum oxide. What is the empirical formula for aluminum oxide?
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Coyle/Tang-Johnson Chemistry Study Guide
9. Find the empirical formula for the following for a compound that is 75% carbon and 25% hydrogen
10. When 20.16g of magnesium oxide reacts with carbon, carbon monoxide and
12.16g of magnesium are produced. What is the empirical formula of magnesium oxide?
11. Calculate the empirical formula for a compound that is 94.1% oxygen and
5.9% hydrogen.
12. Calculate the empirical formula for a compound that is 67.6% mercury, 10.8% sulfur, and 21.6% oxygen.
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Coyle/Tang-Johnson Chemistry Study Guide
MOLECULAR FORMULAS
13. What is a molecular formula?
To find a molecular formula :
1) You will be given the molar mass of the compound
2) Find the empirical formula if it is not given
3) Find the empirical formula mass (efm) of the compound
4) Divide the given molar mass by the efm to get a whole number (n)
5) Multiply this whole number (n) by each formula subscript to get the molecular formula.
Ex: What is the molecular formula for a compound whose molar mass is 34g and whose empirical formula is HO?
Empirical formula mass = 17g (molar mass H = 1g + molar mass O = 16g)
molar mass = 34g = 2 (

this is n , so multiply it by the subscripts) empirical formula mass 17g
(HO)
2
= H
2
O
2
PRACTICE:
14. Find the molecular formula of a compound that is 62g/mol and whose empirical formula is CH
3
O.
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