Three Gas Laws in SCH3U
Presenter: Joy McCourt
Mentor: Nick Fox
Background
The unit on gases and atmospheric chemistry in SCH3U is strand F in the current curriculum for the course. While
the STSE expectations for the unit focus on air quality, the majority of the unit focuses on discovering and using
quantitative relationships that exist between the pressure, volume, temperature and amount of an ideal gas.
Connections to stoichiometry and mass also appear in the expectations for the unit. One of two units in the
course with a heavy mathematical component, many students find this unit challenging. It is the goal of this
concept presentation to suggest strategies for teaching three of the gas laws explored in the unit—Boyle’s Law,
Charles’ Law, and Gay-Lussac’s Law—in such a way as to help students better succeed in learning them.
Curriculum Expectations
Overall:
F2. investigate gas laws that explain the behaviour of gases, and solve related problems;
F3. demonstrate an understanding of the laws that explain the behaviour of gases.
Specific:
Inquiry:
F2.2 determine, through inquiry, the quantitative and graphical relationships between the pressure,
volume, and temperature of a gas [PR, AI]
F2.3 solve quantitative problems by performing calculations based on Boyle’s law, Charles’s law, GayLussac’s law, the combined gas law, Dalton’s law of partial pressures, and the ideal gas law [AI]
Knowledge and Understanding:
F3.4 describe, for an ideal gas, the quantitative relationships that exist between the variables of pressure,
volume, temperature, and amount of substance
F3.5 explain Dalton’s law of partial pressures, Boyle’s law, Charles’s law, Gay-Lussac’s law, the combined
gas law, and the ideal gas law
Position of Unit in Course
Rationale for starting the course with the gas laws unit:
- approach of doing so, using gases to introduce the mole, has been successfully used by others (e.g.,
presented at November 2006 STAO ScienceWorks workshop on SCH3U)
- helps students have a realistic picture of the course at the beginning—it’s not all math and logic, but they
are required (& helps us get a hard unit out of the way)
- students easily understand that increasing the amount of a gas causes the volume of a balloon to
increase—very natural introduction to the mole
- Avogadro’s hypothesis arose from studying gas-state reactions.
Position of Concepts in Unit (assuming this unit is taught first)
- Introductory information:
o Math issues: significant figures, rearranging equations
o Introduction to conversion factors: pressure unit conversions
- States of Matter (particle speed, types of motion, forces between particles, and how these affect the
state’s properties)
- How pressure affects volume (Boyle’s Law)
- How temperature affects volume and pressure (Charles’ Law, Gay-Lussac’s Law) (including using the
Kelvin scale)
- The combined gas law
-
-
Pressure when multiple gases are involved (Dalton’s Law--the hardest one for my students!), including
composition of the atmosphere (note: some texts do this law later)
How the amount of gas affects volume, pressure, and therefore temperature (the ideal gas law, including
an introduction to the concept of the mole; molar volume)
Connections to the mass of a gas (including molar mass and using “The Mole Highway” or “The Y
Diagram” to convert between mass and volume)—including “The SCH3U Lighter Lab”! (see posted Best
Practice)
Address the expectation dealing with stoichiometry within the unit on quantities in chemical reactions.
Hands-On Possibilities
Qualitative
Play Time! Give students some simple activities to work through in a guided way, and have them come up with
explanations / simple relationships between the variables involved.
These activities help students associate the concepts with qualitative, real-world visuals that can help them
understand other applications of the laws.
Examples:
- Using a film canister or balloon to explore Boyle’s Law (increasing pressure decreases volume, until the
container can no longer withstand the pressure)
- Rinsing a pop bottle with hot water, then sealing it and using it to discuss Charles’ Law
- Using the warning label of an appropriately-labeled can of some compressed product (shaving cream,
etc.) to discuss (not demonstrate!) Gay-Lussac’s Law (heating a sealed, rigid container of gas causes the
pressure inside to increase, until the container can no longer withstand the pressure)
Quantitative
- 2001 course text by McGraw-Hill Ryerson includes:
o using a C-clamp and a sealed plastic pipette to examine Boyles’ Law
o gradually heating a sealed plastic pipette to examine Charles’ Law; Rockley and Rockley (1995) give a
similar, but more advanced, method
- Vernier probeware: Boyle’s Law lab
- Purchase various sets of apparatus available on the market
o kits by John Eix and Irwin Talesnick (the latter of “Idea Bank” fame)
(http://www.s17science.com/)
o kit for overhead use available from Nova Scientific Online
(http://www.nova-so.ca/product/CGL-83404)
Societal Applications
- Gas cylinder safety (helium tanks, welders’ acetylene and oxygen tanks, etc.)
o Compressed Gas Cylinder Training Video - Missile Hazard
(http://www.youtube.com/watch?v=pe9gYRXQTTY)
o MythBusters (http://www.youtube.com/watch?v=ejEJGNLTo84)
- Occupations and situations that use compressed gases: anesthesia, welding, water treatment…
- Popcorn, and some aspects of rising dough
- Hot air ballooning
- “The bends” (diving)
Safety
The main safety concerns when studying this unit have to do with:
- Pressurized gases
- High temperatures
Electrical safety when using hot plates and
probes
-
Fire concerns when using Bunsen burners
(e.g., to seal plastic pipettes)
-
Fumes created while sealing plastic pipettes
Taking care not to break thermometers
Misconceptions and Student Difficulties
Difficulty: Gay-Lussac’s Law…or rather, getting past its name.
Solutions:
- Model what it looks like to discuss the law without being tripped up by its name. If discomfort arises
among students, make sensitive use of this “teachable moment.”
- Are you using the 2002 Nelson textbook? It actually refers to the law as “the pressure-temperature law,”
using the rationale that “history of science references say that Charles, Dalton and Gay-Lussac were all
involved in investigating this relationship, with Charles and Dalton doing their work before Gay-Lussac” (p.
435). This approach could be considered for very immature classes (at the cost of some science history
and an opportunity for dialogue).
Difficulty: figuring out what law is at work / what kind of change is taking place
From Horton (2007): “For example, Herbert Beall (1994) lectured college freshmen on the second law of
thermodynamics and the ideal gas laws. After the lecture only 11% were able to correctly predict the
effect that opening a cylinder of compressed gas would have on the temperature of the gas.”
Solutions:
- Include qualitative hands-on examples to give the students “hooks” on which to hang the concepts and
relate to new situations.
- Teach students to examine units and descriptions provided for clues. Practice this as a class.
- Use the GRASP method mentioned in previous presentations: What are you given? What are you asked
to find? Which equation relates those quantities?
Difficulty: visualizing what’s going on at the molecular level
Solutions:
- put it in real-world terms. Jumpy, energetic dancers dancing to fast-paced music collide more often and
put a lot more pressure on the dance floor than dancers doing a slow dance. (They’re probably also
warmer!) The molecules of a gas move around more at a high temperature and collide with the container
more often, leading to higher pressure.
- use a simulator (either as a demo or as a worksheet-guided computer lab activity)
o http://www.chem.ufl.edu/~itl/2045/MH_sims/gas_sim.html is visually appealing and can be used to
illustrate the effect of changing n as well, but cannot be used for Charles’ Law
o http://intro.chem.okstate.edu/1314f00/laboratory/glp.htm is useful, but bare-bones
Difficulty: rearranging equations
-
May know how to rearrange in addition/subtraction examples (x + 5 = 7), but inappropriately try to
add/subtract when multiplying or dividing are required
May have always struggled with solving equations in their math courses, and can only solve for x in the
previous example by using guess-and-check.
Solution:
- Not quickly dealt with, so have patience.
- Help students understand what is going on in the equation as is…“PV” means the P is multiplying the V. If
I only want V, I must undo that multiplication by dividing both sides of the equation by P.
- Go back to easier mathematical examples: how can you solve for x if 3x = 12?
-
See if the student’s math teachers can offer insight.
Challenging/Supporting Different Levels of Classes
Ready for a Challenge
- Take them through the full work-up of each law, including the use of proportionality constants
- Embed less scaffolding / fewer supports in questions
- Expect more detailed explanations of the situation at the microscopic level
- Expect them to explain why all three variables are actually involved in a given situation
Need More Support
- Help them to see the connection between what we expect in the real world and the form of the relevant
equation; set up ratios as you rearrange the equations
- Embed more scaffolding and support into questions; teach students to work carefully through calculations
by using GRASP or a similar strategy
- Teach them to make a common-sense prediction first, then check their calculated answer against their
prediction
- Fewer questions / extra time.
Supporting Different Kinds of Learners
Visual style/Spatial intelligence:
 may find the microscopic picture easier to
grasp than other students
 again, check the reasonableness of answers
by considering the real-world picture
Linguistic intelligence:
 Reading style: assigned to consolidate inclass learning
 Writing style: summarizing (in writing) those
readings and their hands-on work and
writing notes/filling in blanks during lectures
 Auditory style: may prefer to spend more
time listening to and taking in the lecture
than on taking notes
 Verbal: may benefit from “talking through”
practice problems with a partner or the
teacher.
Interpersonal learners may also benefit from “talking
through” practice problems.
Kinesthetic learners will benefit the most from
hands-on learning approaches already mentioned.
Naturalistic learners may find concepts easier to
grasp by connecting them to everyday occurrences,
such as the popping of popcorn and breathing
Logical-mathematical students will likely find the
calculations easier than their classmates; if they lack
a Visual style, the simulations may help them until
they can make a logical connection to what’s going
on in the situation.
Musical:
 Later in the unit: for 99 cents, you can
download Professor Boggs’ “Hey, Avogadro”
about the ideal gas law:
http://www.songsforteaching.com/science/
professorboggs/avogadrosnumber.htm
 Challenge all students to use what works for
them when trying to remember the laws,
such as by making up a song (but they can
only sing it in their heads during quizzes ).
At least one teacher makes this an
assignment: see one example of student
product at
http://www.youtube.com/watch?v=Hbb9dG
mU0r0
Intrapersonal intelligence…how can these learners
best be supported, other than by allowing them to
work independently (a strategy that doesn’t actually
connect to self-knowledge)?
Suggested Lesson Sequence:
Description of Activity
Day 1 – Exploring Qualitative Relationships
 “Play Time”: Groups work on activities leading
to qualitative development of pressurevolume-temperature relationships
 Consolidation: groups report findings back to
class
 Chalk-and-talk with use of simulations, pictures
and real-world analogies: what is going on at
the microscopic level?
 Use Boyle’s Law apparatus to draw out
quantitative patterns in the relationship
between pressure and volume
Day 2 – Using Boyle’s Law
 Chalk-and-talk: Boyle’s Law, and using PredictGRASP-Check to solve Boyle’s Law problems
 Students work on a few practice problems
alone or in pairs
 Demonstrate procedure for Charles’ Law lab
students will perform next day
Day 3 – Charles’ Law lab
 Students complete a lab in pairs introducing
them to Charles’ law, absolute zero and the
importance of the Kelvin scale
 If desired and time permits, schedule time in a
computer lab for analysis and graphing of data
in Excel
Teaching/Learning
Strategies
Expectations
Addressed
Learning Styles
and Intelligences
Assessment
Guided inquiry
F3.5
F3.4
Student as instructor
Direct instruction
Technology
Demonstration
Direct instruction
Collaborative problemsolving
Demonstration
Guided inquiry
Technology (option)
Interpersonal
Kinesthetic
Visual
Verbal
Auditory
Logicalmathematical
F2.3
F3.4
F3.5
F2.2
F3.4
Logicalmathematical
Auditory
Writing (fill in
handout)
Interpersonal
Intrapersonal
Kinesthetic
Interpersonal
Visual
Logicalmathematical
Verbal reports from each
group
Exit pass: “Will the _____
increase or decrease?” for
2 different situations
(qualitative only!)
During examples,
diagnose students’ ability
to rearrange equations
Clarifications sought by
students; common errors
/ wrong answers
Collect lab sheets for
assessment of data
analysis and discussion
questions
Day 4 –Charles’ & Gay-Lussac’s Laws; Putting it All
Together
 Consolidate students’ lab results
 Chalk-and-talk: Charles’ Law (and, after
demonstration, Gay-Lussac’s Law), the Kelvin
scale, and using Predict-GRASP-Check to solve
 If available, use apparatus designed to
demonstrate Gay-Lussac’s Law
 Groups work on problems which can be solved
using the three gas laws studied, using GRASP
to identify the appropriate law and solve;
groups then present their solution process
Day 5
Evaluate understanding of and ability to use gas
laws studied to date
Socratic discussion
Direct instruction
F3.4
F2.3
F3.5
Demonstration
Collaborative problemsolving
F2
F3
Verbal
Auditory
Logicalmathematical
Writing (fill in
handout)
Visual
Students’ ability to
verbalize relationship
discovered
Students’ ability to
rearrange these equations
(more difficult than
Boyle’s Law)
Students’ ability to
identify an appropriate
law to solve a problem
Evaluation: quiz on
Boyle’s, Charles’ and GayLussac’s laws
Continue with strategies to teach the combined gas
law and other concepts in the course.
References (also see above for links to apparatus suppliers, videos, and online simulations)
- Ontario Science curriculum (2008 revision) (The guideline for all we do)
- Horton, C. (2004). Student Misconceptions and Preconceptions in Chemistry. California Journal of Science Education, 7 (2), 1531-2488.
(Used in research of student misconceptions)
- Jenkins, Frank, et al. (2002). Chemistry 11. Toronto: Nelson. (Course text for previous curriculum)
- Mustoe, Frank, et al. (2001). Chemistry 11. Toronto: McGraw-Hill Ryerson. (Course text for previous curriculum)
- Rockley, Natalie L. (1995). A Charles’ Law Experiment for Beginning Students. Journal of Chemical Education, 72 (2), 179-181 (As noted
above, this article outlines a way of performing a Charles’ Law experiment with more sophisticated equipment, including a discussion of a
reasonable error range to expect)
- STAO ScienceWorks SCH3U workshop (November 2006) (Presenter suggested approach of teaching the gas laws unit as the first unit in
the course)