Chemistry
Name:
Period:
Chemical Quantities
Practice
#1
Practice
#2
Practice
#3
Practice
#4
Practice
#5
Practice
#6
Practice
#7
Practice
#8
Practice
#9
Practice
#10
5 points x _____ stamps = _____/ 50
There are many ways to measure matter. You can count it, measure its mass, or measure its volume. For
example, you can go to the grocery store and buy 5 oranges by counting them. You could also buy 3 pounds of
oranges by weighing it mass. Or lastly, you can buy oranges by seeing how many oranges can fit in the volume
of your plastic bag. Sometimes, we use words to describe a certain amount of objects. For example, we use the
word dozen to describe the number 12. Below is a list of a few other words that describe an exact number.
Word
Pair of Shoes
Dozen of Eggs
Score
(“4 scores and 7 years ago”)
Gross of Pencils
Ream of Paper
Mole of an Element
Exact Number
2
12
20
144
500
6.02 x 1023
WHAT IS A MOLE?
Counting objects like oranges is relatively simple because the size of the object is relatively large. But imaging
counting grains of sand on a beach, or the amount of atoms it takes to make up a human body. These would be
tireless and endless tasks. In chemistry, scientists have come up with a word to represent a large amount of
particles. A mole is a measurement that represents 6.02 x 1023 particles. It also equals 6.02 x 1023 molecules.
PRACTICE #1: Converting Moles ↔ Particles
1. How many moles are in 2.17 x 1023 particles of Br2?
2. How many moles are in 34.9 x 1026 particles of HCl?
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3. How many particles are in 0.034 moles of NaOH?
4. How many particles are in 53.9 moles of PCl3?
5. How many moles are in 4.8 x 1022 particles of Silver?
6. How many particles are in 0.000300 mole of AuCl3?
7. How many particles are in 0.300 mole of H3PO4?
8. How many moles are in 7.8 x 1021 particles of Cadmium?
9. How many particles are in 0.00550 mole of CH4?
10. How many moles are in 5.0x 1022 particles of NH4OH?
0.360
2.0x1022
5.80x102
ANSWERS TO PRACTICE #1
0.80
3.31x1021
3.24x1025
1.81x1023
PRACTICE #2: Converting Moles ↔ Molecules
1. How many moles are in 4.65 x 1024 molecules of NO2?
2. How many moles are in 9.21 x 1025 molecules of O3?
3. How many molecules are in 0.76 moles of C2H4?
2
0.013
0.083
20
1.81x10
4. How many molecules are in 5.21 moles of SiO2?
5. How many moles are in 8.5 x 1022 molecules of Gold?
6. How many moles are in 2.00 x 1026 molecules of Na2SO4?
7. How many molecules are in 1.95 mole of HNO3?
8. How many molecules are in 3.2 moles of O2?
9. How many moles are in 7.20 x 1025 molecules of H2O?
10. How many molecules are in 0.09 moles of CH4?
5x1022
1.17x1024
4.6x1023
ANSWERS TO PRACTICE #2
332
0.14
2
1.20x10
3.14x1024
PRACTICE #3: Converting Moles ↔ Atoms
1. How many moles of Mg are in 1.25 x 1023 atoms of Mg?
2. How many moles of Silicon are in 2.80 x 1024 atoms of Silicon?
3. How many atoms are in 2.12 mol of propane (C3H8)?
4. How many atoms are in 1.14 mol of SO3?
3
153
7.72
24
1.9x10
5. How many moles of Iron are in 4.3 x 1022 atoms of H2O?
6. How many atoms are in 2.00 mole of HC2H3O2?
7. How many atoms are in 5.00 mole of Ag2O?
8. Calculate the number of atoms in 2.23 mole of N2.
9. How many atoms are in 71 moles of O3?
10. How many moles are in 6.28 x 1028atoms of Tungsten?
ANSWERS TO PRACTICE #3
9.03X1024
1.3X1026
0.208
2.75X1024
4.65
1.04X105
2.68X1024
1.40X1025
0.024
9.63X1024
MOLAR MASS
If you look on the periodic table, you can find the atomic masses of different elements. The atomic mass of an
element is expressed in grams per mole (g/mol). To find the molar mass of a compound, add the masses of the
elements in the compound.
Practice #4: Find the molar mass of the following elements or compounds
1. Li
8. (NH4)2CO3
2. Al
9. AlCl3
3. PCl3
10. KMnO4
4. CO2
11. TeF4
5. H2O2
12. ZnO
6. NaHCO3
13. CaSO4
7. Al2(SO4)3
14. Ba(SCN)2
4
15. H2CO3
18. NH3
16. Cu2O
19. NH4Cl
17. K2S
20. LiOH
137.32
6.94
53.5
ANSWERS TO PRACTICE #4
158.04
203.6
62.03
23.95
17.04
143.1
26.98
133.33
342.01
84.01
44.01
136.15
110.27
253.51
81.39
86.11
34.02
MASS ↔ MOLE CONVERSION
o You can use molar mass to convert between mass and mole of an element or compound.
o To convert from mass to mole, divide by molar mass.
o To convert from mole to mass, multiply by molar mass.
PRACTICE #5: Convert between the mass and mole of an element or compound
1. What is the mass of 3.00 moles of NaCl?
2. What is the mass of 9.45 mol of Al2O3?
3. How many grams are in 2.5 mol of Fe(OH)2?
4. What is the mass of 4.52 x 10-3 moles of C20H42?
5. How many moles are in 10.0 grams of Na2SO4?
6. How many moles are in 92.2 grams of Fe2O3.
7. Find the number of moles in 3.70 x 10-1 grams of Boron.
8. Calculate the number of moles in 75.0 grams of N2O3.
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9. Calculate the mass of 1.000 mole of CaCl2.
10. Calculate grams in 3.0000 moles of CO2.
11. Calculate number of moles in 32.0 g of CH4.
12. Determine mass in grams of 40.0 moles of Na2CO3.
13. Calculate the mass of 2.23 mol of N2 molecule.
14. Calculate moles in 510.0 g of Al2S3.
15. How many moles are in 27.00 g of H2O.
16. Determine mass in grams of 1.0000 mole of C12H22O11.
17. Find mass in grams of 9.03 moles of H2S.
18. Determine grams in 1.204 mole of NH3.
19. You need 0.0100 mole of PbCrO4. How much should you weigh on the scale?
20. How many moles are in 6.40 g of HBr?
ANSWERS TO PRACTICE #5
0.0791
20.52
4240
111.0
220
0.0704
0.0342
1.99
3.396
3.23
6
1.498
132.03
0.987
0.577
175
308
1.29
964
342.34
62.6
MOLE ↔ VOLUME CONVERSION
o The volume of gas is usually measured at a STP, which is 0ºC and 1 atmosphere (atm)
o At STP, 1 mole or 6.02 x 1023 particles of gas occupies a volume of 22.4 L/mol
PRACTICE #6: Convert between mole and volume of a gas at STP
1. What is the volume of 0.375 mole of oxygen gas at STP?
2. What is the volume of 0.60 mol of SO2 gas at STP?
3. How many moles are in 4.2L of gas at STP?
4. What is the volume of 3.20 x 10-3 mol of CO2 gas at STP?
5. What is the volume of 3.7 mol of N2 gas at STP?
6. How many moles are in 0.223L of gas at STP?
7. What is the volume of 1.25 mol of He gas at STP?
8. What is the volume of 0.335 mol of C2H6 gas at STP?
9. What is the volume of 6.78 moles of He gas at STP?
10. What is the volume of 89.1 moles of CO gas at STP?
11. What is the volume of 3.4 x 104 moles of O3 gas at STP
12. What is the volume of 2.4 moles of F2 gas at STP?
54
152
7.6x105
ANSWERS TO PRACTICE #6
83
0.19 7
13
28.0
0.00996
7.50
0.0717
2.00x103
8.40
MOLAR MASS ↔ DENISTY CONVERSION
o You can use molar mass to convert to density, or density to convert to molar mass
PRACTICE #7: Convert between molar mass and density
1. What is the molar mass of a gas that has a density of 1.964g/L at STP?
2. What is the molar mass of a gas at STP with a density of 3.58g/L?
3. What is the density of Krypton gas at STP rounded to 3 significant figures?
4. What is the density of Sulfur gas at STP rounded to 3 significant figures?
5. The density of a gas at STP is 45.2g/L. What is its molar mass?
6. What is the density of Phosphorus gas at STP rounded to 3 significant figures?
7. What is the molar mass of a gas that has a density of 7.8g/L at STP?
8. What is the density of Argon gas at STP rounded to 3 significant figures?
9. What is the density of Xenon gas at STP rounded to 3 significant figures?
10. What is the molar mass of a gas that has a density of 3.84 x 106g/L at STP?
1010
1.43
1.38
ANSWERS TO PRACTICE #7
8.60x107
1.78
3.74
80.2
8
5.86
43.99
170
PERCENT COMPOSITION
o Percent composition is the relative amounts of the elements in a compound
o It consists of a percent value for each element in the compound with the total values adding up to 100%
PRACTICE #8: Calculate the percent composition for each of the following
1. When a 13.60-gram sample of a compound containing only Mg and O decomposes, 5.40g of O is
obtained. What is the % composition of this compound?
2. A compound is formed when 9.03 grams of Mg combines with 3.48 grams of Nitrogen. What is the
percent composition of this compound?
3. When a 14.2-gram sample of HgO is decomposed into its elements by heating, 13.2g of Hg is obtained.
What is the % composition of the compound?
4. What is the percent composition of the compound formed when 2.70 grams of aluminum combine with
oxygen to form 5.10 grams of aluminum oxide?
5. Calculate % composition when 13.3g of Fe combines with 5.7g of O.
6. Calculate the percent composition of C3H8.
7. Calculate the percent composition of C2H6.
8. Calculate the percent composition of NaHSO4.
9. Calculate the percent composition of NH3.
10. Find the percent compositions of all of the elements in the following compound: Al2(SO4)3
ANSWERS TO PRACTICE #8
(52.9% Al, 47.1% O)
(60.3% Mg, 39.7% O)
(19.2% Na, 0.83% H, 26.7% S, 53.3% O)
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(72.2% Mg, 27.8% N)
(7.0% O, 93.0% Hg)
(81.8% C, 18.2% H)
(70% Fe, 30% O)
(80.0% C, 20.0% H)
(82.4% N, 17.6% H)
(15.8%Al, 28.1%S, 56.1%O)
EMPIRICAL FORMULA
o Empirical Formula shows the smallest whole-number ratio of the atoms in the compound
o Change each % into grams, then convert from grams to mole. Divide each of the numbers by the
smallest mole value. If necessary, multiple by a number to get a whole number.
PRACTICE #9: Calculate the empirical formula of the following
1. A compound is analyzed and found to contain 25.9% nitrogen and 74.1% oxygen. What is the empirical
formula of the compound?
2. Calculate the empirical formula of a compound that contains 94.1% O and 5.9% H.
3. Calculate the empirical formula of a compound that contains 67.6% Hg, 10.8% S, and 21.6% O.
4. What is the empirical formula of a compound that contains 62.1%C, 13.8% H, and 24.1% N?
5. What is the empirical formula of a compound that is 56.6% K, 8.7% C, and 34.7% O?
6. Write the empirical formula for a compound composed of: 72% iron and 27.6% oxygen
7. Write the empirical formula for a compound composed of: 0.0130 mol C, 0.0390 mol H, 0.0065 mol O
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8. Write the empirical formula for a compound composed of: 0.556g carbon and 0.0933g hydrogen
9. Write the empirical formula for a compound composed of: 11.66 g iron, 5.01 g oxygen
10. Write the empirical formula for a compound composed of: 40.0% C, 6.7% H, and 53.3% O
11. Write the empirical formula for a compound composed of: 15.8% carbon and 84.2% sulfur
12. Write the empirical formula for a compound composed of: 43.6% phosphorus and 56.4% oxygen
13. Write the empirical formula for a compound composed of: 28.7% K, 1.5% H, 22.8% P and 47.0% O
N2O5
C3H8N
ANSWERS TO PRACTICE #9
HgSO4
OH
P2O5
K2CO3
Fe2O4
CH2O
KH2PO4
CS2
Fe2O3
CH2
C2H6O
MOLECULAR FORMULA
o Molecular Formula tells the actual number of each atom in a molecule of the compound
o Calculate the empirical formula mass (EFM), then divide the molar mass by the EFM, then multiply the
formula subscripts by the value.
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PRACTICE #10: Calculate the molecular formula of the following
1. Calculate the molecular formula of a compound whose molar mass is 60.0 g/mol and has an empirical
formula of CH4N.
2. Find the molecular formula of antifreeze with a mm of 62 g/mol and an empirical formula of CH3O.
3. What is the molecular formula of a compound with empirical formula CClN and a mm of 184.5g/mol?
4. The empirical formula of a compound is CH2O, and its mm is 90g/mol. What is its molecular formula?
5. The empirical formula of a compound is HgCl with a mm of 472.2g/mol. What’s the molecular formula?
6. What is the molecular formula of a compound that is 94.1% O and 5.9% H, with a molar mass of 34g.
7. What is the molecular formula of a compound that is 50.7% C, 4.2% H, 45.1% O with a mm of 142g?
8. Write the molecular formula for a compound: mm of 70.0g/mol and empirical formula of CH2.
9. Write the molecular formula for a compound: mm of 46.g/mol and empirical formula of NO2.
10. Write the molecular formula for the following compound: empirical formula CH, molar mass = 78 g/mol
11. Write the molecular formula for the following: empirical formula NO2, molar mass = 92.02 g/mol
12. Write the molecular formula for caffeine: 49.5% C, 5.15% H, 28.9% N, 16.5% O, molar mass=195g/mol
C6H6O4
Hg2Cl2
H2O2
ANSWERS TO PRACTICE #10
C3H6O3
C2H12
C2H8N2
6O2
C8H10N4O2
N2O4
C6H6
NO2
C3Cl3N3
C5H10
Chapter 10 Review Sheet
1. How many grams are in 5.66 mol of CaCO3? (566 g)
2. Find the number of moles in 508 grams of C2H6O. (11.0 mol)
3. Calculate the volume in liters of 1.50 mole of Cl2 at STP. (33.6 L)
4. What is the molar mass of an elemental gas at STP with a density of 1.7824 g/L. (39.9 g/mol)
5. How many molecules are in 5.02 moles of a substance?
6. How many atoms are in 3.09 moles of C2H4?
7. Which of the following pure iron samples contains the largest number of atoms?
a. 6.70 g
b. 0.110 mole
c. 7.83 x 1022 atoms
8. Arrange the following in order of increasing mass. Hint: convert each one to mass
a. 10.4 g of sulfur
b. 0.179 moles of iron
c. 6.33 x 1025 atoms of hydrogen
d. 0.77 moles of N2
9. Can the molecular formula of a compound ever be the same as the empirical formula for the
compound? Explain you answer.
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