1. Can’t Judge a Powder (B)
By Lin Wozniewski

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 Can’t 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?

5. 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

8. 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

9. 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

10. 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.

11. 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

12. 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.

13. 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.

14. Scoring the Exam 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

15. Resources Sample Observation Sheet Sample Question Sheet Sample Key
Sample Question Sheet
Sample Key