Property of ACS USNCO – Not for use as USNCO National Exam after May 1, 2022
Distributed by the American Chemical Society, 1155 16
th
Street, N.W., Washington, DC 20036
All rights reserved. Printed in U.S.A.
2022 U.S. NATIONAL
CHEMISTRY OLYMPIAD
NATIONAL EXAM PART III
Prepared by the American Chemical Society Chemistry Olympiad Examinations Task Force
OLYMPIAD LABORATORY PRACTICAL TASK FORCE
Kelli Slunt, Chair, University of Mary Washington, Fredericksburg, VA
Payton Bailey, University of Mary Washington, Fredericksburg, VA
Jesse Bernstein, Miami Country Day School, Miami FL (retired)
Chloe Boyd, University of Mary Washington, Fredericksburg, VA
Stacia Brooks, University of Mary Washington, Fredericksburg, VA
Alexsandra DaSilva, SUNY, Binghamton, NY
Myra Halpin, NC School of Science & Mathematics, Durham, NC (retired)
Nicolas Hamel, Clackamas Community College, Oregon City, OR
Tiffany Pham, University of Mary Washington, Fredericksburg, VA
Innocent Pumure, University of Central Missouri, Warrensburg, MO
Lawrence Wilkinson, ExxonMobil, Baton Rouge, LA
DIRECTIONS TO THE EXAMINER
The laboratory practical part of the National Olympiad Examination is designed to test skills related to the laboratory. Because the
format of this part of the test is quite different from the first two parts, there is a separate, detailed set of instructions for the examiner.
This gives explicit directions for setting up and administering the laboratory practical.
There are three parts to the National Olympiad Examination. You have the option of administering the three parts in any order, and
you are free to schedule rest breaks between parts.
Part I 60 questions single-answer multiple-choice 1 hour, 30 minutes
Part II 8 questions problem-solving, explanations 1 hour, 45 minutes
Part III 2 lab questions laboratory practical 1 hour, 30 minutes
There are two laboratory tasks to be completed during the 90 minutes allotted to this part of the test. Students may carry out the two
tasks in any order they wish and move directly from one to the other within the allotted time. Each procedure must be approved for
safety by the examiner before the student begins that procedure.
A periodic table and other useful information are provided on page two for student reference.
Students should be permitted to use non-programmable calculators. The use of a programmable calculator, cell phone, watch,
or any other device that can access the internet or make copies or photographs during the exam is grounds for
disqualification.
Students are permitted to request one replacement or refill of a chemical during the laboratory period. Please indicate on the
exam sheet the item replaced or refilled.
DIRECTIONS TO THE EXAMINEE - DO NOT TURN THE PAGE UNTIL DIRECTED TO DO SO.
WHEN DIRECTED, TURN TO PAGE 3 AND READ THE INTRODUCTION AND SAFETY CONSIDERATIONS
CAREFULLY BEFORE YOU PROCEED. There are two laboratory-related tasks for you to complete during the next 90 minutes.
There is no need to stop between tasks or to do them in the given order. Simply proceed at your own pace from one to the other, using
your time productively. You are required to have a procedure for each problem approved for safety by an examiner before you carry
out any experimentation on that problem. You are permitted to use a non-programmable calculator. At the end of the 90 minutes, all
answer sheets should be turned in. Be sure that you have filled in all the required information at the top of each answer sheet.
Carefully follow all directions from your examiner for safety procedures and the proper disposal of chemicals at your examination
site.
Do not forget to turn in your U.S. citizenship/Green Card Holder statement before leaving the testing site today.
STUDENT USNCO ID:
Page 2 Property of ACS USNCO – Not for use as USNCO National Exam after May 1, 2022
ABBREVIATIONS AND SYMBOLS
CONSTANTS
amount of substance n
ampere A
atmosphere atm
atomic mass unit u
Avogadro constant N
A
Celsius temperature °C
centi– prefix c
coulomb C
density d
electromotive force E
energy of activation E
a
enthalpy H
entropy S
equilibrium constant K
Faraday constant F
free energy G
frequency ν
gas constant R
gram g
hour h
joule J
kelvin K
kilo– prefix k
liter L
measure of pressure mm Hg
milli– prefix m
molal m
molar M
molar mass M
mole mol
Planck’s constant h
pressure P
rate constant k
reaction quotient Q
second s
speed of light c
temperature, K T
time t
vapor pressure VP
volt V
volume V
R = 8.314 J mol
–
1
K
–
1
R = 0.08314 L bar mol
–
1
K
–
1
F = 96,500 C mol
–
1
F = 96,500 J V
–1
mol
–
1
N
A
= 6.022 × 10
23
mol
–
1
h = 6.626 × 10
–34
J s
c = 2.998 × 10
8
m s
–
1
0 °C = 273.15 K
1 atm = 1.013 bar = 760 mm Hg
Specific heat capacity of H
2
O =
4.184 J g
–
1
K
–
1
EQUATIONS
o
ln
RT
EE Q
nF
= −
o
1
ln constant
H
K
RT
−∆
= +
2
1 12
11
ln
a
E
k
k RT T
= −
1
PERIODIC TABLE OF THE ELEMENTS 18
1A 8A
1
H
1.008
2 13 14 15 16 17
2A 3A 4A 5A 6A 7A
2
He
4.003
3
Li
6.941
4
Be
9.012
5
B
10.81
6
C
12.01
7
N
14.01
8
O
16.00
9
F
19.00
10
Ne
20.18
11
Na
22.99
12
Mg
24.31
3
3B
4
4B
5
5B
6
6B
7
7B
8
8B
9
8B
10
8B
11
1B
12
2B
13
Al
26.98
14
Si
28.09
15
P
30.97
16
S
32.07
17
Cl
35.45
18
Ar
39.95
19
K
39.10
20
Ca
40.08
21
Sc
44.96
22
Ti
47.88
23
V
50.94
24
Cr
52.00
25
Mn
54.94
26
Fe
55.85
27
Co
58.93
28
Ni
58.69
29
Cu
63.55
30
Zn
65.39
31
Ga
69.72
32
Ge
72.61
33
As
74.92
34
Se
78.97
35
Br
79.90
36
Kr
83.80
37
Rb
85.47
38
Sr
87.62
39
Y
88.91
40
Zr
91.22
41
Nb
92.91
42
Mo
95.95
43
Tc
(98)
44
Ru
101.1
45
Rh
102.9
46
Pd
106.4
47
Ag
107.9
48
Cd
112.4
49
In
114.8
50
Sn
118.7
51
Sb
121.8
52
Te
127.6
53
I
126.9
54
Xe
131.3
55
Cs
132.9
56
Ba
137.3
57
La
138.9
72
Hf
178.5
73
Ta
180.9
74
W
183.8
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.1
79
Au
197.0
80
Hg
200.6
81
Tl
204.4
82
Pb
207.2
83
Bi
209.0
84
Po
(209)
85
At
(210)
86
Rn
(222)
87
Fr
(223)
88
Ra
(226)
89
Ac
(227)
104
Rf
(261)
105
Db
(262)
106
Sg
(263)
107
Bh
(262)
108
Hs
(265)
109
Mt
(266)
110
Ds
(281)
111
Rg
(272)
112
Cn
(285)
113
Nh
(286)
114
Fl
(289)
115
Mc
(289)
116
Lv
(293)
117
Ts
(294)
118
Og
(294)
58
Ce
140.1
59
Pr
140.9
60
Nd
144.2
61
Pm
(145)
62
Sm
150.4
63
Eu
152.0
64
Gd
157.3
65
Tb
158.9
66
Dy
162.5
67
Ho
164.9
68
Er
167.3
69
Tm
168.9
70
Yb
173.0
71
Lu
175.0
90
Th
232.0
91
Pa
231.0
92
U
238.0
93
Np
(237)
94
Pu
(244)
95
Am
(243)
96
Cm
(247)
97
Bk
(247)
98
Cf
(251)
99
Es
(252)
100
Fm
(257)
101
Md
(258)
102
No
(259)
103
Lr
(262)
Property of ACS USNCO – Not for use as USNCO National Exam after May 1, 2022 Page 3
Student Instructions
Introduction
These problems test your ability to design and carry out laboratory experiments and to draw conclusions from your experimental
work. You will be graded on your experimental design, on your skills in data collection, and on the accuracy and precision of your
results. Clarity of thinking and communication are also components of successful solutions to these problems, so make your written
responses as clear and concise as possible.
Safety Considerations
You are required to wear approved eye protection at all times during this laboratory practical. You also must follow all
directions given by your examiner for dealing with spills and with disposal of wastes.
Lab Problem 1
Question: Antacids are a class of medications that neutralize acid in the stomach. Determine the moles of HCl, simulating stomach
acid that can be neutralized by a tablet of commercial antacid.
Lab Problem 2
Question: Design and carry out an experiment to determine the specific identity of the substance in each of six numbered vials. Each
vial contains one of these substances.
baking soda (sodium bicarbonate)
borax (sodium tetraborate)
cornstarch (polysaccharide of glucose)
Epsom salts (magnesium sulfate)
powdered sugar (sucrose and corn starch)
washing soda (sodium carbonate)
Using the materials provided (including distilled water, 10% HCl, 10% NaOH, 2% iodine solution, bromothymol blue, and
phenolphthalein), devise and carry out an experiment to correctly determine the contents of each vial.
Page 4 Property of ACS USNCO – Not for use as USNCO National Exam after May 1, 2022
Answer Sheet for Laboratory Practical Problem 1
Student's Name: ____________________________________________________________________________
Student's School:____________________________________________________________________________
Proctor's Name:_____________________________________________________________________________
ACS Local Section Name:_____________________________________________________________________
1. Give a brief description of your experimental plan.
2. Record your data/observations.
For safety reasons before beginning your experiment, you must get Examiner’s Initials:________
approval from the examiner.
STUDENT USNCO ID:
Property of ACS USNCO – Not for use as USNCO National Exam after May 1, 2022 Page 5
3. Show all calculations.
4. A typical Tums tablet weighs 1.3 g. The amount of stomach acid that can be neutralized by the tablet is:
________________.
Examiner please indicate the item replaced or refilled provided:
Page 6 Property of ACS USNCO – Not for use as USNCO National Exam after May 1, 2022
Answer Sheet for Laboratory Practical Problem 2
Student's Name: ____________________________________________________________________________
Student's School:____________________________________________________________________________
Proctor's Name:_____________________________________________________________________________
ACS Local Section Name:_____________________________________________________________________
1. Give a brief description of your experimental plan.
2. Record your data and other observations.
For safety reasons, before beginning your experiment, you must get Examiner’s Initials:_________
approval from the examiner
STUDENT USNCO ID:
Property of ACS USNCO – Not for use as USNCO National Exam after May 1, 2022 Page 7
2. Record your data and other observations (continued).
3. Identify the substance in each unknown vial, giving a brief justification for that choice.
Unknown #
Contains
Justification
1
2
3
4
5
6
Examiner please indicate the item replaced or refilled provided:
a
Property of ACS USNCO – 2022 USNCO National Exam Part III Examiner’s Instructions Page 1
2022 U.S. NATIONAL
CHEMISTRY OLYMPIAD
NATIONAL EXAM PART III
EXAMINER’S INSTRUCTIONS
Prepared by the American Chemical Society Chemistry Olympiad Examinations Task Force
OLYMPIAD LABORATORY PRACTICAL TASK FORCE
Kelli Slunt, Chair, University of Mary Washington, Fredericksburg, VA
Payton Bailey, University of Mary Washington, Fredericksburg, VA
Jesse Bernstein, Miami Country Day School, Miami FL (retired)
Chloe Boyd, University of Mary Washington, Fredericksburg, VA
Stacia Brooks, University of Mary Washington, Fredericksburg, VA
Alexsandra DaSilva, SUNY, Binghamton, NY
Myra Halpin, NC School of Science & Mathematics, Durham, NC (retired)
Nicolas Hamel, Clackamas Community College, Oregon City, OR
Tiffany Pham, University of Mary Washington, Fredericksburg, VA
Innocent Pumure, University of Central Missouri, Warrensburg, MO
Lawrence Wilkinson, ExxonMobil, Baton Rouge, LA
Thank you for administering the 2020 USNCO laboratory practical on behalf of your Local Section. It is essential that you follow the
instructions provided in order to ensure consistency of results nationwide. There may be considerable temptation to assist the students
after they begin the lab exercise. It is extremely important that you do not lend any assistance or hints whatsoever to the students once
they begin work. As in international competition, the students are not allowed to speak to anyone until the activity is complete.
The equipment needed for each student for both lab exercises should be available at his/her lab station or table when the students enter
the room. The equipment should be initially placed and the materials separated for Lab Problem #1 and for Lab Problem #2.
Students are permitted to request one replacement or refill of a chemical during the laboratory period. Please i
ndicate on the
exam sheet the item replaced or refilled.
It is your responsibility to ensure that all students wear approved eye protection at all times, tie back long hair into a ponytail,
and wear close-toed shoes during this laboratory practical. A lab coat or apron for each student is desirable but not
mandatory. You will also need to give students explicit directions for handling spills and for disposing of waste materials,
following approved safety practices for your examination site. Please check and follow procedures appropriate for your site.
After the students have settled, read the following instructions to the students.
Hello, my name is ________. Welcome to the lab practical portion of the U.S. National Chemistry Olympiad Examination. In
this part of the exam, we will be assessing your lab skills and your ability to reason through a laboratory problem and
communicate its results. Do not touch any of the equipment in front of you until you are instructed to do so.
You will be asked to complete two laboratory problems. All the materials and equipment you may want to use to solve each
problem has been set out for you and is grouped by the number of the problem. You may use equipment from one problem to
work on the other problem, but the suggested ideal equipment and chemicals to be used for each problem has been grouped
for you. You will have one hour and thirty minutes to complete the two problems. You may choose to start with either
problem. You are required to have a procedure for each problem approved for safety by an examiner. (Remember that
approval does not mean that your procedure will be successful – it is a safety approval.) When you are ready for an examiner
to come to your station for each safety approval, please raise your hand.
Safety is an important consideration during the lab practical. You must wear safety goggles at all times. Please wash off any
chemicals spilled on your skin or clothing with large amounts of tap water.
The appropriate procedures for disposing of solutions at the end of this lab practical are:
____________________________________________________________________________________________________
____________________________________________________________________________________________________
a
Page 2 Property of ACS USNCO – 2022 USNCO National Exam Part III Examiner’s Instructions
We are about to begin the lab practical. Please do not turn the page until directed to do so, but read the directions on the
front page. Are they any questions before we begin?
Distribute Part III booklets and again remind students not to turn the page until the instruction is given. Part III contains student
instructions and answer sheets for both laboratory problems. There is a periodic table on page two of the booklet. Allow students
enough time to read the brief cover directions.
Do not turn to page three until directed to do so. When you start to work, be sure to fill out all of the information at the top of
the answer sheets. Are they any additional questions?
If there are no further questions, the students should be ready to start Part III.
You may begin.
After one hour and thirty minutes, give the following directions.
This is the end of the lab practical. Please stop and bring me your answer sheets. Thank you for your cooperation during this
portion of the exam.
Collect all the lab materials. Make sure that the student has filled in his or her name and other required information on the answer
sheets. At this point, you might wish to take a few minutes to discuss the lab practical with the students. They can learn about possible
observations and interpretations and you can acquire feedback as to what they actually did and how they reacted to the problems. After
this discussion, please take a few minutes to complete the Post-Exam Questionnaire that was sent by e-mail through Formsite; this
information will be extremely useful to the USNCO subcommittee as they prepare for next year’s exam.
Please remember to return the answer sheets from Part III, the Scantron sheets from Part I, and the ‘Blue Books” from Part
II in the UPS Next Day return envelope you were provided to this address:
American Chemical Society
U.S. National Chemistry Olympiad
1155 16th Street, NW – Room 834
Washington, DC 20036
The label on the UPS Express Pak envelope should have this address and your return address already. The cost of the shipping is
billed to ACS USNCO. You can keep a copy of the tracking number to allow you to track your shipment.
May 9, 2022 is the absolute deadline for receipt of the exam material. Materials received after this deadline CANNOT be graded.
Be sure to have your envelope sent no later than May 7, 2022 for it to arrive on time.
THERE WIL BE NO EXCEPTIONS TO THIS DEADLINE DUE TO THE TIGHT SCHEDULE FOR GRADING THIS
EXAMINATION.
NOTE THAT THE EXAMINER WILL NEED TO INITIAL EACH STUDENT’S EXPERIMENTAL PLAN. PLEASE DO
NOT COMMENT ON THE PLAN OTHER THAN LOOKING FOR ANY POTENTIAL UNSAFE PRACTICES.
a
Property of ACS USNCO – 2022 USNCO National Exam Part III Examiner’s Instructions Page 3
Laboratory Problem #1
Materials needed for problem #1:
• One (1) graduated cylinder, 25 mL – can substitute with 10 and/or 100 mL
• Two (2) Beral pipets, with 0.25 mL graduations
o Suggested Beral pipets are:
Fisher brand catalog# 13-711-9AM
Samco Scientific – Thermo Fisher catalog number 212
• One (1) glass stirring rod – for both problems #1 and 2
• One (1) spatula – for both problems #1 and 2
• One (1) hot plate – stirring is not needed and should not be used
• Three (3) beakers, 100 or 150 mL
• pH indicator strips range 1.0-12.0, 12 per student
o Suggested indicator strips
Fluka Analytical Mat # 10184429
Fisher brand catalog #13-640-508
• Two (2) pieces of wax paper or glassine weigh paper – used to crush tablets
• Distilled or deionized water, at least 500 mL, in a wash bottle labeled appropriately – for both problems #1 and 2
• Access to paper towels and a sink with running water – for both problems #1 and 2
Chemicals needed for problem #1:
• Phenolphthalein indicator, 0.5% (wt in 1:1 ethanol/water), 0.5 mL in a labelled Beral pipet or a vial with a dropper – for both
problems #1 and 2
• Three (3), TUMS peppermint antacid tablets – PLEASE remove from original packaging and place in a labelled plastic bag.
These will be provided to you by ACS. DO NOT provide packaging information to the students.
• Standardized HCl, 0.5 M reported to three significant figures, 100 mL per student
• Standardized NaOH, 0.40-0.45 M reported to three significant figures, 50 mL per student
Standardization instructions for NaOH, to be standardized by the coordinator:
1. Dissolve 20 grams of solid NaOH in enough distilled or deoionized water to create one liter solution.
2. Weigh out approximately 0.8 grams of potassium hydrogen phthalate (KHP, molecular weight 204.23 g/mol) to at least 3
decimal places and dissolve in 50-75 mL of water in an Erlenmeyer flask. Record the amount of KHP used.
3. Add 2-3 drops of phenolphthalein indicator to the KHP solution.
4. Titrate the solution with prepared NaOH solution until a faint pink endpoint. Record volume of NaOH solution used in the
titration.
5. Repeat.
6. Convert grams of KHP to mol NaOH noting a 1:1 mole ratio of KHP to NaOH.
7. Divide moles of NaOH by the volume of NaOH used to determine molarity.
8. Report the average molarity on the labels for the students.
Standardization instructions for HCl, to be standardized by the coordinator:
1. Dilute 83.3 mL of 6M HCl with enough distilled or deoionized water to create 1 L of 0.5 M HCl.
2. Pipet or use a buret to transfer 20.0 mL of HCl to an Erlenmeyer flask. Record the volume of HCl used.
3. Add 2-3 drops of phenolphalein.
4. Titrate the solution with the previously standardized NaOH solution, recording the volume of NaOH used in the titration.
Repeat trials.
5. Convert the volume of standardized NaOH added to solution to moles of HCl (1:1 stoichiometry) using the molarity of
NaOH.
6. Divide the number of moles of HCl by the volume of HCl used in the titration to determine molarity.
7. Report the average molarity to three significant figures on the label for the students.
Phenolphthalein indicator, 0.5% (wt in 1:1 ethanol/water), 0
.5 mL in a labelled Beral pipet
Either purchase prepared indicator or prepare by dissolving 1.0 g of phenolphthalein in 100 mL of a mixture of ethanol and water (50
mL ethanol and 50 mL water).
a
Page 4 Property of ACS USNCO – 2022 USNCO National Exam Part III Examiner’s Instructions
Dispense approximately 0.5 mL in a Beral pipet or a vial with a dropper and place a label on the pipet/vial. For the pipet, store with
the bulb end of the pipet down.
Laboratory Problem #2
Materials needed for problem #2:
• Four (4) Beral pipets – these do not need to be graduated but can have graduations
• One (1) glass stirring rod – for both problems #1 and 2
• Twelve (12) test tubes
• One (1) test tube rack or two (2) test tube racks depending on number of slots in the racks
• One (1) spatula -– for both problems #1 and 2
• One (1) plastic or ceramic well plate, 6 or 12 wells per plate
• One (1) distilled or deionized water, at least 500 mL, in a wash bottle labeled appropriately – for both problems #1 and 2
• Access to paper towels and a sink with running water – for both problems #1 and 2
Chemicals needed for problem #2:
• Phenolphthalein indicator, 0.5% (wt in 1:1 ethanol/water), 1.0 mL in a labelled Beral pipet or a vial with a dropper (same one
for problem #1)
• Bromothymol blue indicator, 0.04% (wt in water), 0.5 mL in a labelled Beral pipet or a vial with a dropper
• Iodine–Potassium Iodide Solution, 5 mL per student
• HCl, 10%, 10 mL of solution (does not need to be standardized)
• NaOH, 10%, 10 mL of solution (does not need to be standardized)
• Unknowns – please label each of these samples with unknown number and not the identity of the substance
o unknown #1: cornstarch, 2 g per student
o unknown #2: baking soda (sodium bicarbonate), 2 g per student
o unknown #3: epsom salts (magnesium sulfate), 2 g per student – can use anhydrous MgSO
4
or an available hydrated
forms
o unknown#4: powdered sugar, 2 g per student
o unknown #5: washing soda (sodium carbonate), 2 g per student
o unknown #6: borax (sodium tetraborate), 2 g per student – ca
n use commercially available borax from a grocery
store or pure sodium tetraborate
Bromothymol blue indicator, 0.
04%, 0.5 mL in a labelled Beral pipet
• Either purchase prepared indicator or prepare by dissolving 0.04 g of bromothymol blue in 50 mL of distilled or deoinized
water and then dilute to 100 mL with water.
• Dispense approximately 0.5 mL in a Beral pipet or a vial with a dropper and place a label on the pipet or vial. For the pipet,
store with the bulb end of the pipet down.
Iodine–Po
tassium Iodide Solution
Dissolve 15 g of potassium iodide in 125 mL of distilled or deoionize water; add 3 g of iodine; stir to
dissolve, then dilute to 1 L. Store in a dark bottle.
Waste disposal:
The solutions should not be disposed of down the drain. Place any waste in a designated waste container.
Suggested Laboratory Setup Photos
Note – phenolphalein and bromothymol blue could be provided in a labelled dispensing bottle rather than the pipet as shown.
PLEASE remove TUMS tablets from original packa
ging and place in a labelled plastic bag. DO NOT provide TUMS
packaging information to the students.
a
Property of ACS USNCO – 2022 USNCO National Exam Part III Examiner’s Instructions Page 5
DO NOT provide names of the unknowns on the bottles of white solids.
See photos for suggested set-up on the next page.
a
Page 6 Property of ACS USNCO – 2022 USNCO National Exam Part III Examiner’s Instructions
a
Property of ACS USNCO – 2022 USNCO National Exam Part III Examiner’s Instructions Page 7
2022 UNITED STATES NATIONAL CHEMISTRY OLYMPIAD
National Exam Part III RUBRIC
Prepared by the American Chemical Society Chemistry Olympiad Laboratory Practical Task Force
Lab Problem 1
Question: Antacids are a class of medications that neutralize acid in the stomach. Determine
the moles of HCl, simulating stomach acid, that can be neutralized by a tablet of commercial
antacid.
Answer Sheet Questions
1. Give a brief description of your experimental plan (5 points)
One suggested approach – back titration
• Indication that a back titration with excess HCl will be used to solve the problem
• Students may plan to test titration (observation of endpoint) with the HCl, NaOH,
and indicator
• Experimental details on the titration
o Mix tablet, HCl, and indicator and heat the solution to near boiling to
release excess CO
2
. Remove from heat, allow to cool and test with pH
indicator paper to ensure excess acid is present. Titrate with NaOH until
the color turns from colorless (or white due to presence of the tablet) to
pink.
• Students may attempt to titrate by dissolving the tablet in water and titrating
with HCl, but this is an inaccurate method.
o Care should be taken to prevent overheating as the fillers present in the
tablet may burn when heating on the hot plate or the water can
evaporate.
• Determine the volume of a drop of liquid from a Beral pipette
• Replicate Measurements
Another approach – determine amount of carbon dioxide lost after neutralization
• Indication that measurement of loss of carbon dioxide will be determined by
decrease in mass
• Experimental details
o Mass of all items before mixing – making sure to include the glassware
for the reaction
o Mass of items after mixing
o Allow time for the reaction to occur – stirring, heating, and waiting until
no visible gas remains in the solution and the reaction between the
antacid and HCl concluded. Remove from heat, allow to cool, and
determine mass after reaction.
o Ensure an excess of HCl was added to the tablet – using pH strips to check
the pH.
o Care should be taken to prevent overheating as the fillers present in the
tablet may burn when heating on the hot plate or the water can
evaporate.
• Replicate Measurements
2. Record your data/observations (6 points)
Back titration
• Recorded mass of antacid tablet used
• Recorded volume of a drop of liquid from a Beral pipette
• Clear data table indicating starting volume of HCl and volume of NaOH used to
neutralize the solution
• Observations- color changes observed in titrations
• Clear indication of how number of drops are converted to volume or how the
volume of solutions used was determined
Quantification of carbon dioxide lost after neutralization
• Clear data table including starting and ending masses of antacid, solutions, and
glassware and volumes of HCl used
• Observations- could include the expulsion of gas, the final masses were recorded
after all visible gas was removed, pH of the solution after excess HCl was added
• Clear indication of how number of drops are converted to volume or how the
volume of solutions used was determined
3. Show all calculations (7 points)
Back titration
• Calculate the number of moles needed to dissolve the total amount of calcium
carbonate in the tablet
• Calculate the total moles of HCl that was used to completely dissolve the antacid
tablet and still have excess in solution.
• Calculate the moles of NaOH added to reach the endpoint = moles of excess HCl
• Calculate the moles of HCl that reacted with the calcium carbonate in the antacid
tablet
• Average value – from duplicate trials
Quantification of carbon dioxide lost after neutralization
• Mass of carbon dioxide lost
• Mass of calcium carbonate in the antacid tablet
• Calculate the moles of HCl that reacted with the calcium carbonate in the antacid
tablet
• Average value – from duplicate trials
4. A typical Tums tablet weighs 1.3 g. The amount of stomach acid that can be neutralized
by the tablet is: _____________. (7 points)
• Experimental range: 0.00986 mol – 0.0106 mol HCl per 1.3 g tablet
• Accuracy of value
0.00980 – 0.0106 moles full credit
0.00882- 0.00979 or 0.0105 – 0.0116 moles 5 points
0.00784-0.00881 or 0.0117-0.0127 moles 3 point
any other answers (in moles) 0 points
Answers in units other than moles of HCl were converted to moles and then graded
using the scale above.
Lab Problem 2
Question: Design and carry out an experiment to determine the specific identity of the
substance in each of six numbered vials. Each vial contains one of these substances.
• baking soda (sodium bicarbonate)
• borax (sodium tetraborate)
• cornstarch (polysaccharide of glucose)
• Epsom salts (magnesium sulfate)
• powdered sugar (sucrose and corn starch)
• washing soda (sodium carbonate)
Using the materials provided (including distilled water, 10% HCl, 10% NaOH, 2% iodine solution,
bromothymol blue, and phenolphthalein), devise and carry out an experiment to correctly
determine the contents of each vial.
Answer Sheet Questions
1. Give a brief description of your experimental plan (5 points)
• use equal amounts of substances (i.e. end of a spatula, small amount in the
bottom of test tube or well)
• add a set volume of reagent (i.e. 0.25 mL) or add the reagents dropwise
• stir samples and observe color changes, formation of gas, formation of
precipitate
2. Record your data/observations (8 points)
• Clear data table or flow chart indicating substances combined and the results of
the tests performed
• observations (color changes, production of gas, solubility, formation of
precipitate) – see table at end with sample results
3. Identify the substance in each unknown vial, giving a brief justification for that choice. (12
points)
Unknown
#
Contains
Justification
1
Cornstarch
Insoluble in water, interacts with starch and turn
blue-black
2
Baking Soda (sodium
bicarbonate)
Produces a gas in the presence of an acid (HCl or
vinegar),
3
Epsom salts
(magnesium sulfate)
Forms a white precipitate in the presence of
hydroxide
4
Powdered sugar
Soluble in water, interacts with starch and turns
blue-black (smaller color change than cornstarch –
indicating less starch present in the sample)
5
Washington soda
(sodium carbonate)
Produces a gas in the presence of an acid, basic in
the presence of phenolphalein (darker pink than
sodium bicarbonate)
6
Borax (sodium
tetraborate)
Soluble in water and aqueous acids but no gas
produced in the presence of acid, basic in the
presence of phenolphalein
Data from White Powder Trials – Data compiled from three students at the University of Mary
Washington
Cornstarch
(unknown1)
Baking
soda
(unknown
2)
Epsom
salts
(unknown
3)
Powdered
sugar
(unknown
4)
Sodium
carbonate
(unknown
5)
Borax
(unknown
6)
Water solubility
Insoluble
Soluble
Soluble
Soluble
Soluble
Sparingly
soluble
10% HCl
solubility
Insoluble
Soluble
and gas
produced
Soluble
Soluble
(Note:
one
student
listed as
insoluble)
Soluble
and gas
produced
Soluble
and no
gas
produced
10% NaOH
reaction
No change
No
change
White ppt
formed
No
change
No
change
No
change
Vinegar
solubility
Insoluble
Soluble
and gas
produced
Soluble
Soluble
(Note:
one
student
listed as
insoluble)
Soluble
and gas
produced
Soluble
and no
gas
produced
Iodine
Dark
blue/black
No
change
No
change
Faint
blue/
black
No
change
No
change
Phenolphthalein
No change
Pale pink
No
change
No
change
Dark pink
pink
Bromothymol
blue
Yellow-blue
green
blue
Yellow
blue
blue
blue
