Critical Thinking in Chemistry
Summary:
Eat candles, prevent water pouring out of holes, stump your students with the
mystery tube. This introductory unit gets students thinking. Then uses student
designed labs to keep them thinking all year long.
Introduction:
As pressures rise to meet test scores, can you still help students become critical
thinkers? Absolutely. At the start of the year, take time to teach the scientific method
with labs that raise questions. Practice being the source of questions, not the fount
of knowledge. By not giving the answer, you encourage your students to think, ask
questions, collaborate and learn to solve problems scientifically. Follow this up with
authentic assessment labs through out the year, and you can build critical thinking
skills.
This introductory unit covers science principals, lab techniques, and class structure.
It also sets the stage for a class that asks questions and students who can use the
scientific method to solve problems. The demonstrations are not original, but the
organization and the fostering of questions is what makes this work. To continue
thinking through out the year, I provide examples of authentic assessment lab
questions for chemistry that can be used through out the year.
Content Standards Covered: Investigation and Experimentation: 1a,d,f,g, and k.
Unit Outline:
Activity
Observing a Candle
Skills
Topics
Make detailed observations,
Senses used in observing,
make a data table, using lab
qualitative vs quantitative
equipment, writing
observation, inference
Three Holed Bottle
Write hypotheses, make
Scientific Method
detailed observations, make a
data table, ask questions
Make a PB&J sandwich Writing a procedure
Clear communication
Mystery Tube
Write hypotheses, write
Scientific Method
conclusions, ask questions,
suggest follow up
experiments, make a model
Student Designed
Ask question, hypothesis,
Scientific Method
bottle Experiment
write procedure, data table,
conclusion
If students need help measuring use mini metric Olympics between PBJ and Mystry
Tube.
Observing a Candle (Standard 1a)
First day of school, have students make observations of a candle. A minimum of 15.
5 before lighting, 5 while lit, and 5 after blown out. Be a detailed as possible, use as
many of your senses as possible (not taste), use any or all of the tools provided
(ruler, electronic balance, graduated cylinder).
Day 2 Analyzing observations (Standard 1a)
Have students look at observations.
Every time they find the word “it”, cross it out and write to what it refers.
How are are the observations organized? In a table? Labeled as to when observed?
What would make the data more clear? Do that. (As a teacher model a table or what
ever structure you think best)
Introduce the idea of qualitative vs quantitative observations. Use student examples.
Also use student’s examples to talk about inference or interpretation: examples
might be: the candle was used before, or the candle is made of wax, or I can smell
burned candle.
Start with a new candle (jicama with ½ peanut). Go around the class and have
students make observations, light the candle at some point, then eat the candle at
some point. Do not act as if anything is unusual. Do not tell the students what you
ate! When they ask, you can say, what did you think it was? Or say it was a candle (it
was, of sorts). This is important! Part of science is becoming comfortable with the
unknown. Also, students need to find answers to questions, not just ask you. You are
setting the tone for the whole year.
Suggested homework: Observing nothing. Go to a place where nothing happens and
make 20 observations. Be as detailed as possible and use as many senses as possible.
Day 3 Writing Hypotheses
Students should have some introduction to the scientific method, then work on
formulating hypotheses. Our school has adopted the If…Then format. If I do a stated
action, then I think this will occur. Frequently in practice, I give students the “if” part
since I have designed the experiment and their guess is the “then” part. For language
learners, I have made a worksheet that is all pictures, and their hypothesis is drawn.
Demonstrate the three holed bottle vertical. Ask what students think will happen
when you remove the tape from the first hole. Write sample hypotheses on the
board. If students state it incorrectly, correctly write it on the board. Have students
vote for which hypothesis they agree with. Often one of the hypotheses is that
nothing will happen. After the vote, see if there is a volunteer who is so confident in
his/her hypothesis that they are willing to sit under the bottle while you perform
the experiment. Then perform the experiment (demonstration). Students record
their observations. You should record them on the board, make sure there is detail.
Then move to the second hole – what do you think will happen when two holes are
open? Students write their hypotheses. Record them on the board; try to make sure
they have detail. Have students vote, ask for a volunteer and perform the second
experiment. Make detailed observations and record on board. Repeat process for
third hole.
Then pair up students and have them repeat the experiment with the cap off and
then with cap on and off, but holding the bottle horizontally, holes down.
Suggested homework: Hopefully this experiment made you wonder. Can you explain
why the bottle behaves the way it did or do you have questions about this
experiment? Are there topics you have heard of that are related to this experiment?
What type of research or follow up experiment might help answer your questions.
(write a paragraph)
Writing Procedures:
Students are notoriously bad for writing vague directions. For example, “measure
the water”. Measure what about the water? the mass, temperature, volume…? And
what water? To help, start with a demonstration. You need a loaf of bread inside bag,
2 plastic knives, a jar of peanut butter and a jar of jelly, maybe a napkin or a paper
towel. Tell the students you are from another planet and you have heard of the
delicacy peanut butter and jelly sandwiches and wish to experience this American
tradition. You have studied the English language through dictionaries and have
working definitions of all words. Have students give directions for you to make this
sandwich. Take all of their directions literally and as if you have no prior knowledge.
For example when they say open the bread bag, if you have never opened a bread
bag, you wouldn’t know how to do it. When they say take a piece of bread out, use
your fingers and rip a smidge of bread from the first slice. Be aware that you are
likely to get messy as unclear jelly and peanut butter directions get your hands into
the jar or on the sandwich.
When you are done with your demonstration. Have students make a list of how to
write a good procedure and (in pairs) have them write a procedure for making a PBJ
sandwich.
Homework: complete PBJ procedure
Making a peanut butter and jelly sandwich
The following day, have students exchange directions and send them to lab tables to
test the procedures. Tell them to follow directions exactly, this is not a test of can
you make a sandwich, but can you write a procedure. Let them fix the sandwich at
the end to make it edible. Who ended up with a good PBJ sandwich? What fixes
could be made to improve their procedure? Have them make the fixes.
Homework: rewrite PBJ directions with fixes or write a note to yourself reminding
you how to write a good procedure, things to add that make directions clear, things
to help you be understood, etc.
Writing conclusions (Using the mystery tube to write conclusion)
The structure of a conclusion in my department follows. Your department should
have an idea of the parts of a conclusion they think are important.
SMHS Department Conclusion Format:
1. restate your hypothesis
2. state your findings
3. State whether your findings prove or disprove your hypothesis
4. Explain your results and give a reasonable explanation for why or why not your
findings didn’t match your hypothesis
5. Offer ideas for a) improving the experiment, b) further experiments, c) questions
you would like to investigate, and/or d) applications in the real world.
Diagram of Mystery Tube: see following website:
http://undsci.berkeley.edu/lessons/mystery_tubes.html
Directions for Instructor:
1. Show tube, number strings (see diagram at end of this document) and ask for
hypothesis about the string connection. Have students draw a picture of what they
think it looks like inside.
2. Make an If … then hypothesis: If I pull string 3, then……?
3. Pull string 3. (string 4 should move)
Write conclusion as a class.
Reset tube strings
5. Ask what will happen if you pull string 2.
Students write hypothesis
Pull string 2 while deceptively holding string 3. String 4 should move.
Write conclusion as individual, but then record one student’s on the board.
6. Repeat steps and pull string 1 while holding string 3. String 4 should move.
Write conclusion (This last conclusion will frequently be confusion. They restate
their hypothesis, state results, say they don’t concur and they have no idea what to
do about it.) Have students pair up; exchange their conclusions and read looking to
see that each conclusion has all the required parts. Share ideas as a class.
Note: I never show students the inside since we are studying chemistry and can’t see
an atom, we just study it’s behavior. Students who can make a mystery tube that
behaves the same do receive extra credit and as a class we can look inside the
student made model, but we never know for sure that it is exactly like the teacher’s
tube. The mystery tube is on the internet, so if you offer extra credit for making a
model, you may want to change the name of the tube; I use the tube of wonder.
Putting it all together:
Return to the bottle demonstration. What do students think is going on? What could
you test to further understand the behavior of the bottle?
As a class develop a list of variables that students could test. Example: hole size, hole
location, substance in bottle, size of bottle, reverse air and water (put empty bottle
in a fish tank and repeat test), etc.
Have pairs choose something to test and then prepare an experiment. They produce
a full lab report. The first day work on writing procedure, hypothesis, procedure, list
equipment and prepare a data table. The next day students return prepared to do
their experiment, class period spent doing experiment and entering data in data
table. Students write a conclusion and turn in completed lab.
If time, have groups share their results as a class and see if group can come up with
understanding of bottle behavior.
Documents to have for unit:
Candle lab directions
Hypothesis Bottle Pictures
Mini Metric Olympics Document or other measuring lab
Writing conclusions (mystery tube)
Bottle Lab Grading Rubric
Bottle Lab (hypothesis writing)
Bottle Lab Preparation
Design labs and their main topics
Mystery tube Diagram:
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