Name ____________________________ Period _____
CRHS Academic Chemistry
Unit 7 - Chemical Quantities
Practice Problems
Due Date
Assignment
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7.1
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7.2
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7.3
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7.4
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7.5
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7.6
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7.7
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Warm-Up
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EC
On-Time (100)
Late (70)
Notes, Homework, Exam Reviews and Their KEYS located on CRHS
Academic Chemistry Website: https://cincochem.pbworks.com
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Unit 7 HW
Day 1
Day 7
Day 2
Day 8
Day 3
Day 9
Day 4
Day 10
Day 5
Day 11
Day 6
Day 12
Unit 7 HW
Page 16
HW 7.1 INTRODUCTION TO THE “MOLE”
Find the molar mass of the compound. Round average atomic mass to the hundredths place. Show units.
1. NaCl
2.
Ca(OH)2
Na =
__________
Ca = __________
Cl =
___________
O = __________
NaCl = __________
H = __________
Ca(OH)2 = ___________
3. Fe2O3
4. Ammonium phosphate
5. Al2(SO4)3
6. Dinitrogen trioxide
7. An alien visits earth. He brings with him an unknown substance. He says, “I believe this substance is like
an Earthly compound; it is either like nitrogen dioxide or nitrogen trioxide. I’m not sure which. All I know
is that its molar mass is 62.01 g.” Which compound did the alien bring with him? Show your work to
receive credit.
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Unit 7 HW
HW 7.2 MOLE TO MASS AND MASS TO MOLE CONVERSIONS
Complete the following conversions using dimensional analysis. Show work!
1. Convert 0.780 mol of calcium cyanide, Ca(CN)2, to mass.
2. How many grams are in 0.50 mol of copper (II) sulfate?
3. Convert 30 g of silicon dihydride to moles.
4. How many moles are in 100 grams of potassium sulfide?
5. Your grandfather has to take 5 grams of aspirin (C 8H8O4) daily for his arthritis. How many moles of aspirin
should he take?
Unit 7 HW
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6. You go to the pawn shop to buy your girlfriend some jewelry. The clerk offers to sell you a necklace that
has 5 grams of gold in it for $300. How many moles of gold are in the necklace?
7. You are conducting a lab experiment to evaluate the reaction between calcium hydroxide and hydrochloric
acid. Your teacher has told you how much of each reactant to use (in moles). You must convert to mass
before you can start. Complete the table and show work below the table.
Name of
Compound
Formula of
Compound
Molar Mass
Moles Needed
calcium hydroxide
2.0 mol
hydrochloric acid
4.0 mol
Mass Needed
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Unit 7 HW
HW 7.3 REPRESENTATIVE PARTICLES
Complete the following conversions using dimensional analysis. Show work!
1. How many moles are in 1.50 x 1023 molecules of nitrogen trihydride?
2. Convert 4.8 moles of calcium carbonate to formula units.
3. How many molecules are in 4.80 x 10 –3 mol bromine gas?
4. There are ___ moles in 3.73 x 1022 formula units of barium chloride.
5. Your doctor prescribes you lithium carbonate for your bipolar disorder. Examine the prescription below.
How many formula units of lithium carbonate will you ingest each day?
Dr. Emilio Avogadro
Date Oct
23, 2012
Kim Estudiante
Patient:
℞: Take 5 mol Lithium
Carbonate
Once daily at bedtime
Signature
E. Avogadro
Unit 7 HW
Page 16
6. The same pawn shop clerk from HW 6.2 says, “Okay, you don’t like that necklace? How about these
earrings? They have 1.00 x 1025 atoms of gold in them!” How many moles of gold is this?
7. A cold pack uses an endothermic reaction to cool its surroundings. Inside a cold pack are 5.33 x 1024 formula
units of ammonium nitrate. How many moles of ammonium nitrate are in a cold pack?
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Unit 7 HW
HW 7.4 MIXED MOLE CONVERSIONS
Complete the following conversions using dimensional analysis. Show work!
1. Convert 3.33 x 1024 atoms of sodium to grams.
2. There are ____ moles in 187 g aluminum.
3. How many grams are in 40 moles of ammonium chloride?
4. How many moles are in 333 g tin (II) fluoride?
5. Convert 5.00 x 1025 molecules hydrogen (H2) to grams.
Unit 7 HW
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6. In 1970, Nobel Prize winning scientist Linus Pauling recommended taking “megadoses” of vitamin C to ward off the
common cold. He suggested taking up to 2.5 grams per day. How many molecules of vitamin C (C 6H8O6) did he
recommend that you should take per day?
7. Have you ever tried the energy drink Crunk!!!? It’smade by Lil’ Jon (the rapper) and it is so yummy! It even has 62
grams of amazing sugar (C12H22O11) per can! That’s like _________ molecules of sugar!
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Unit 7 HW
HW 7.5 PERCENT COMPOSITION
1. Write the formula for percent composition below. Use the formula and the information given in
subsequent questions to complete this assignment.
% composition =
x 100%
2. Find the percent composition of hydrogen in each compound:
a) Ca(OH)2
% of H = __________
b) C2H6
% of H = __________
c) Al (C2H3O2)3
% of H = __________
3. Find the percent composition of each element in these compounds:
a) NaCl
molar mass = __________
% of Na = __________
% of Cl = ___________
b) (NH4)2S
% of N = __________
% of H = __________
% of S = __________
molar mass = __________
Unit 7 HW
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4. A sample of liquid with a mass of 8.657 grams was decomposed into its elements and gave 5.217 grams of
carbon, 0.9620 grams of hydrogen, and 2.478 grams of oxygen. What is the percent composition of this
oxygen in this compound? (hint: you don’t need to calculate molar mass to solve this problem, just use the
formula from question #1)
5. A quantitative analysis of 0.4620 grams of an unknown solid found 0.1945 grams of carbon, 0.02977 grams
of hydrogen and 0.2377 grams of oxygen. Calculate the percent composition of carbon in this compound.
(hint: you don’t need to calculate molar mass to solve this problem, just use the formula from question #1)
6. What is the percentage of Fe in FeCO3 ?
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Unit 7 HW
HW 7.6 EMPIRICAL FORMULA
Answer the following questions concerning empirical formulae. Use the steps outlined in your notes.
1. Determine the empirical formula for a compound containing 19.55 grams potassium and 4.00 grams
oxygen.
Step 1 –
Step 2 –
Step 3 -
2. A compound contains 174.86 grams of iron and 74.14 grams of oxygen. Construct the empirical formula.
3. Sodium sulfite is a meat preservative and sodium sulfate is a laxative. Your grandmother gives you a side
of beef for your birthday and you’d like to keep it from rotting. You’ve found a sample of a compound of
sodium that contains 36.5 grams of sodium, 25.4 grams of sulfur, and 38.1 grams of oxygen. Do you have a
laxative or the meat preservative you so desperately need?
Unit 7 HW
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4. As lead arson investigator with the Houston Fire Department you find a small sample of the accelerant
(fuel) that caused a fire that took the lives of 11 people in an urban apartment complex. You run the
sample through a mass spectrometer and find that it contains 37.5% carbon, 12.5% hydrogen, and 50.0%
oxygen, by mass. Determine the empirical formula of this substance.
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Unit 7 HW
HW 7.7 MOLECULAR FORMULA
Answer the following questions concerning molecular formulae. Use the steps outlined in your notes.
1. Find the molecular formula for a compound with a molar mass of 90.04 g/mol and an empirical formula of
CHO2.
Step 1:
Step 2:
Step 3:
2. Find the molecular formula for a compound with 46.68% nitrogen and 53.32% oxygen and a molar mass of
60.01 g/mol.
3. Elaidic acid is the primary trans fatty acid present in partially hydrogenated oils used in food production.
Calculate the molecular formula for elaidic acid given that it has an empirical formula of C 9H17O1 and a
mass of 282 g/mol.
4. Strychnine, a deadly poison, has a mass of 334 amu and a percentage composition of 75.42% carbon,
6.63% hydrogen, 8.38% nitrogen, and 9.57% oxygen. What is the molecular formula of strychnine?
Unit 7 HW
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Common Polyatomic Ions List
20
Common Polyatomic Ions
Name
acetate
ammonium
carbonate
chlorate
chlorite
chromate
cyanide
dichromate
hydrogen carbonate
hydroxide
Name
hypochlorite
nitrate
nitrite
perchlorate
permanganate
phosphate
phosphite
silicate
sulfate
sulfite
Ion
C2H3O2– or CH3COO–
NH4+
CO32–
ClO3–
ClO2–
CrO42–
CN–
Cr2O72–
HCO3–
OH–
How to key scientific notation into a TI calculator:
Type in 6.02 x 1023:
Should display:
How to key molar mass into a TI calculator in ONE STEP!:
Example: Na2SO4
Roman Numerals for Transition Metals 1-6
1 = I
2 = II
3 = III
4 = IV
5 = V
6 = VI
Ion
ClO–
NO3–
NO2–
ClO4–
MnO4–
PO43–
PO33–
SiO32–
SO42–
SO32–
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Unit 7 HW