Can

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Cant Judge a Powder(B)

• By Lin Wozniewski
• lwoz_at_iun.edu

2
Safety

• Students must wear
• 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

3
What Students Can Bring

• 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

4
What Students Cant Bring

• Reference Materials
• Calculators
• Writing instruments of any kind
• ANY materials other than on previous slide
• Ranking below those who have followed the rules

The Penalty?
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What Supervisors Will Provide

• 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

6
What Supervisors MAY Provide

• 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

7
Main Focus

• Observations
• The distinction between an observation and an
  inference
• How to prepare students
• Scoring the Exam
• Resources

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Observations

• 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

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Observations

• Students need to learn to write down
  observations, not inferences.
• Students need to be as specific as possible.
• 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
• 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

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Observations

• Students should do tests on the reagents they are
  given as well as the powder.
• 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.

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Observation Inference

• 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

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Observations

• The questions the event supervisor is likely to
  ask can be divided into two main categories
• Standard Questions
• What color is the powder?
• Is it a powder or a crystal or a granule
• Etc
• Powder specific questions
• You can not ask if dissolving the powder in water
  is exothermic if the powder is insoluble in
  water.
• Etc.

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How to Prepare Students

• 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.

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Scoring the Exam

• This is best done as a group activity if possible
• If there are few enough exams (lt12) 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

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Resources

• Sample Observation Sheet
• http//www.tufts.edu/as/wright_center/products/sci
  _olympiad/cant_judge_a_powder/piqua_regional_2005_
  obser_sht.pdf
• Sample Question Sheet
• http//www.tufts.edu/as/wright_center/products/sci
  _olympiad/cant_judge_a_powder/piqu_regionals_2005.
  pdf
• Sample Key
• http//www.tufts.edu/as/wright_center/products/sci
  _olympiad/cant_judge_a_powder/piqua_regional_2005_
  answr_key.pdf