UCLA, GK-12 Science & Mathematics in Los Angeles Urban Schools
http://www.nslc.ucla.edu/STEP/GK12/index.html
What is the Value of R?
Developed by: S Gould and H. Kang
Teacher Material
California State Standards
Chemistry (Gases and Their Properties)
 4c: Students know how to apply the gas laws to relations between the
pressure, temperature and volume of any amount of an ideal gas or any
mixture of ideal gases.
 4h*: Students know how to solve problems by using the ideal gas law in
the form PV=nRT.
Investigation and Experimentation (Grades 9 to 12)
 1a: Select and use appropriate tools and technology to perform tests,
collect data, analyze relationships and display data.
 1b: Identify and communicate sources of unavoidable experimental
error.
 1c: Identify possible reasons for inconsistent results, such as sources of
error or uncontrolled conditions.
Synopsis
The purpose of this inquiry-based lesson is to guide students to
conduct an experiment in which they will determine the value of the
ideal gas law constant. Students will design their own experiments
based on the materials provided to determine a value for R. After
collecting data, students will compare their values to the literature
values and suggest reasonable sources of error.
Background This lesson should be implemented near the end of a unit on the
Ideal Gas Law (Standard 4). Students will need to have strong
background before attempting this lesson. Students will need to
know what the nature of the an ideal gas is, the relationship between
pressure, volume, amount and temperature (PV=nRT) of an ideal
gas, how to make observations, and determine sources of error.
One of the essential components of this lab is that each group of
students designs their own procedure. The students will be limited
based on the available materials, but each group will have the
opportunity to perform a different procedure.
The basic reaction will be that of vinegar and baking soda. The
chemical reaction is:
Immediately after forming, the carbonic acid decomposes to water
and carbon dioxide as described by this chemical equation:
Page 1 of 8
UCLA, GK-12 Science & Mathematics in Los Angeles Urban Schools
http://www.nslc.ucla.edu/STEP/GK12/index.html
Objectives
1. Students will conduct design an experiment to determine R
2. Students will develop math skills by calculating R.
3. Students will evaluate their design and test changes to improve their
procedure.
4. Students will learn to identify sources or error.
Suggested Timeline
Day one. Initial design and trial run of procedure. 50 min.
Day two. Data collection and analysis. 50 min.
Materials (for each group, cost)
 Vinegar (of known concentration)
 Baking Soda
 Erlenmeyer Flasks, 2 or 3 if possible (50 mL)
 Beakers, 2 or 3 if possible (50 mL)
 Small plastic bottle (small water bottles make a good option, ~250m mL)
 Balloons (2)
 Plastic Sandwich bags (3)
 Small paper bag
 String, rubber bands and twisty ties (several)
 Calculators
Teacher’s Tips
This lesson requires students to come up with their own procedure. If this is
the first time students have undertaken an experiment like this, additional time and
instruction may be necessary for students to get started.
Classroom Activities
1. Warm up – Review of PV=nRT and the properties of an ideal gas.
2. Students break up into groups of 4-6 (depending on size of the class and
how many groups are manageable)
3. Students will need to read the introduction of their worksheet. It may be
best if the introduction and instructions are read aloud by students so that
everyone has the opportunity to ask questions
4. Students are told to design an experiment based on the information they
have just been presented with.
5. Students are instructed to show their procedure to the teacher BEFORE
trying the experiment. Below are some things to look for
a. Students are using no more than 0.5 g of baking soda
b. Students are using at least 15 mL of Vinegar (they can use more)
Page 2 of 8
UCLA, GK-12 Science & Mathematics in Los Angeles Urban Schools
http://www.nslc.ucla.edu/STEP/GK12/index.html
c. Students are measuring the Temperature, Volume, Pressure, and
Weight/Volume of reagents (in the proper units)
d. NOTE: If no barometer is available for pressure to be measured, the
pressure can be found on-line. Please look at the resources section
for more information.
6. Remind students they will need to test their procedure once and make
changes. The final procedure needs to be repeated 3 times!
7. Students may pour their waste down the drain (as long as commercially
available vinegar and baking soda are used as reagents).
8. Provide time at the end of the class period or the next day have time to
calculate the value of R (more information on how to calculate R is provided
on the student handout).
9. Have students write their average value of R on the board
10. Lead a discussion on why the values may be different (What are the most
likely sources of error).
Resources
Local pressure values can be found on the National Oceanic and Atmospheric
Administration (NOAA)’s website: http://www.noaa.gov/
Page 3 of 8
UCLA, GK-12 Science & Mathematics in Los Angeles Urban Schools
http://www.nslc.ucla.edu/STEP/GK12/index.html
(STUDENT HANDOUT BEGINS)
What is the Value of R??
PART I
DATA COLLECTION
Introduction Today’s lab will focus on the ideal gas law constant. You have already
learned about ideal gases. Now using your knowledge you will design an
experiment to determine the value of R.
Normally you write the ideal gas law equation as PV=nRT, but the
equation can be algebraically re-arranged to: R = PV/nT. R can be
calculated by determining values for P (pressure), V (volume), n (number
of moles) and T (temperature).
When baking soda and vinegar are combine a chemical reaction occurs.
The chemical reaction is described by the following equation:
Carbonic Acid (H2CO3) spontaneously decomposes according to the
following equation:
Carbon dioxide (CO2) is an ideal gas.
Using the above information and the materials provided design a
procedure to determine the value of R. Get your teacher to initial the
design BEFORE you try it!
Materials
 Vinegar (of known concentration)
 Baking Soda
 Erlenmeyer Flasks, 2 or 3 if possible (50 mL)
 Beakers, 2 or 3 if possible (50 mL)
 Small plastic bottle (small water bottles make a good option, ~250m mL)
 Balloons (2)
 Plastic Sandwich bags (3)
 Small paper bag
 String, rubber bands and twisty ties (several)
 Calculators
Page 4 of 8
UCLA, GK-12 Science & Mathematics in Los Angeles Urban Schools
http://www.nslc.ucla.edu/STEP/GK12/index.html
Questions & Data Collection
1. Write out each step of your initial experimental procedure.
Teacher’s Initials _______
2. After testing your procedure once, what improvements can be made?
3. Write out each step of your final procedure.
Teacher’s Initials _______
Page 5 of 8
UCLA, GK-12 Science & Mathematics in Los Angeles Urban Schools
http://www.nslc.ucla.edu/STEP/GK12/index.html
4. What is the limiting reagent? How many moles of the limiting regent are you
using?
5. How many moles (n) of gas are produced during your reaction?
6. Test your procedure at least 3 times. Fill out the following chart with your data.
Pressure (P)
Volume (V)
# of Moles (n)
Temperature (T)
Trial
1
Trial
2
Trial
3
Page 6 of 8
UCLA, GK-12 Science & Mathematics in Los Angeles Urban Schools
http://www.nslc.ucla.edu/STEP/GK12/index.html
Discussion Questions & Data Collection
1. Calculate R for each trial (Remember R = PV/nT), Circle your answers
2. What is your average value for R?
3. Is your value more or less than the known value (given to you by your teacher)
Page 7 of 8
UCLA, GK-12 Science & Mathematics in Los Angeles Urban Schools
http://www.nslc.ucla.edu/STEP/GK12/index.html
4. What are some sources of error in your experimental design?
5. What changes would you make to your procedure to reduce the error?
(STUDENT HANDOUT ENDS)
Page 8 of 8