Can’t Judge a Powder(B)

By Lin Wozniewski

lwoz@iun.edu

Disclaimer

This presentation was prepared using draft rules.  There may be some changes in the final copy of the rules.  The rules which will be in your Coaches Manual and Student Manuals will be the official rules.

Safety

Students must wear: Closed shoes Slacks or skirts that come to the ankles Lab coat or lab apron Indirect vent or unvented chemical splash proof

goggles. No impact glasses or visorgogs are permitted

Sleeved Shirt (if wearing a lab apron)Sleeved Shirt (if wearing a lab apron)

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

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?

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

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

Main Focus

Observations The distinction between an observation and

an inference How to prepare students Scoring the Exam Resources

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

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

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.

Observation & Inference If the student attempts to dissolve the .1g of the

powder in 1 ml of water and the temperature goes down from 22.1C to 20.9C, 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

Observation vs. Inference-What’s the Difference Observations are things that you use your

five senses to discern. (No-you are not allowed to taste or touch anything in this lab!)

Inferences are anything that does not use your senses to discern. So you can see a thermometer and observe a

temperature or a temperature change. But you have to infer that the act of dissolving

then takes in or gives off heat based on your observation of the temperature going up or down.

Observation Time Please take ~10-15 minutes to make as many

observations as possible on the powder. Use the pencil in the kit, the HCl, NaOH, & I2 as

well as the balance, thermometer, conductivity meter, graduated cylinders, beakers, etc.

This will work best if you make the observations as you think middle school level children would make them and not like the trained scientific observer educators that you are.

Please use a pseudonym or your school name and not your name to do this.

Questions

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.

Question time

Please use the numbers on your observation sheets to answer the questions on the question sheet

Please use the pen to write on the question sheet

Please use the same pseudonym. If you know the answer to a question, but did

not write down an observation on it, you can write the answer on the line.

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.

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

Practice Scoring Please exchange papers around the tables. You will need both the question and observation

sheets You will see that the observation sheets have a

place to mark if it is an observation or inference. Now we will look at question 1 Does anyone have an observation number to

answer the question? If so, please (one at a time) tell me what the observations say

The point here is not the “right” answer, but the “best” answer.

Resources

For Event Supervisors http://mypage.iu.edu/~lwoz/socrime/index.htm

For Lesson Plans for classroom use http://mypage.iu.edu/~lwoz/socrime/index.htm

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