Can’t Judge a Powder
(B)
By Lin Wozniewski
lwoz@iun.edu
Safety
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Students must wear:
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Closed shoes
Slacks or skirts that come to the ankles
Sleeved shirts
Lab coat or lab apron
Indirect vent or unvented chemical splash proof
goggles. No impact glasses or visorgogs are
permitted
What Students Can Bring
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pHydrion paper
hand lens
9 volt conductivity tester (no testers will be allowed
that run on 120 volts.)
Beral pipettes or eye droppers
Containers appropriate for testing conductivity and
solubility (spot plates, beakers, etc. are fine)
Test tube holder and test tube rack if using test
tubes
Spatula
Stirring rod
What Students Can’t Bring
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Reference Materials
Calculators
Writing instruments of any kind
ANY materials other than on previous slide
The Penalty?
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Ranking below those who have followed the
rules
What Supervisors Will Provide
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1.0 M NaOH
1.0 M HCl
Distilled (deionized) water
Two different colored writing implements
Paper Toweling
The observation sheet
The questions/scoring sheet
What Supervisors MAY Provide
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Thermometer
Balance
Hot plate
Anything else the supervisor decides to
distribute. If the supervisor feels instructions
are needed in order to use something
provided, the instructions will be available
Main Focus
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Observations
The distinction between an observation and
an inference
How to prepare students
Scoring the Exam
Resources
Observations
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Emphasize to students that the purpose of this
lab is NOT to identify the powder. (That is the
Science Crime Buster event-not this one)
The purpose is to characterize the powder!
This event hits all of the Middle School National
Physical Science Standards.
Therefore it is an excellent event to actually
use in the classroom to teach observation and
the difference between observation and
inference
Observations
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Students need to learn to write down
observations, not inferences.
Students need to be as specific as possible.
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While both flour & cornstarch might at first glance be
described as “white powders”, flour is generally more
of an ivory white or creamy white, whereas
cornstarch is more bright white
Students should be as quantitative as possible
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Students should state how many grams of the substance
were attempted to dissolve in how many ml of water and
from what temperature to what temperature the water
changed during how long a time
Observations
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Students should do tests on the reagents
they are given as well as the powder.
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If you do not know for sure if the liquid you are
attempting to dissolved the solid in does or does
not conduct electricity, you can not say for sure
what the solid did
If you do not know what the temperature of the
liquid was before you start dissolving, you can not
know by how much the temperature changed.
Observation & Inference
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If the student attempts to dissolve the .1g of the
powder in 1 ml of water and the temperature
goes down from 22.1C to 20.9C, that is an
observation
If instead the student writes down that
dissolving the powder is an endothermic
process, that is an inference.
You would use the first observation to answer
the question of whether or not the dissolving is
exothermic or endothermic.
But you would get less points for answer 2
Observations
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The questions the event supervisor is likely to
ask can be divided into two main categories:
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“Standard Questions”
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What color is the powder?
Is it a powder or a crystal or a granule
Etc
“Powder specific questions”
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You can not ask if dissolving the powder in water is
exothermic if the powder is insoluble in water.
Etc.
How to Prepare Students
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You will want to create a number of tests for
various powders where the team members
preparing for the event practice making
observations and then get the questions and
have to use their observations to answer the
questions.
The tougher you can make your questions, the
better the students will get.
It is not easy to think of observations to make on
a single powder with only a few reagents for 20
minutes.
Scoring the Exam
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This is best done as a group activity if possible
If there are few enough exams (<~12) two
people can divide the exams between them.
Then the observations that support each
question are looked at and ranked.
The best observations are awarded 5 points, the
next best 4
“Observations” that are really inferences can get
a maximum of only 3.
Incomplete observations receive less points
Resources
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Sample Observation Sheet
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Sample Question Sheet
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http://www.tufts.edu/as/wright_center/products/sci
_olympiad/cant_judge_a_powder/piqua_regional_
2005_obser_sht.pdf
http://www.tufts.edu/as/wright_center/products/sci
_olympiad/cant_judge_a_powder/piqu_regionals_
2005.pdf
Sample Key
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http://www.tufts.edu/as/wright_center/products/sci
_olympiad/cant_judge_a_powder/piqua_regional_
2005_answr_key.pdf