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

Long-Sleeved Shirt (if wearing a lab apron) Gloves are encouraged

What Students Can Bring

test tubes & racks, spot plates, well plates, reaction plates, beakers or similar small containers for mixing

something for scooping & stirring pH or Hydrion paper hand lens(es) Beral pipettes 9-Volt Conductivity tester paper towels Test tube brush

Conductivity Meters

Do not have to be fancy or expensive but can be

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 Substance 1 M HCl 1 M NaOH 2 Different writing instruments Waste Container Wash bottle of Distilled Water (ROI) Instructions about whether refills of the powder

are allowed Instructions on how to use probes or extra

reagents

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.

How to Prepare Students Have students start by observing powders and

reagents and doing sample tests Students need to make the observations on the

reagents first, and then the same observations on the solutions (if any)

Students need to make observations with any “extra” reagents or equipment the event supervisor gives

Students need to get out of the habit of trying to answer the question. They put the observation number as the answer

Coach or assistant scores test and goes over results with students

How to Prepare Students

Have students get out powders and make up tests for each other Students score tests themselves This event is very much like Write-It, Do-It.

Students will get unbelievably better if they have to make up questions and score results.

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.

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

Questions?

Thank you

Time to Play -Observations Before you is a powder, a spot plate, microspatula,

stir rod, conductivity meter, DI, conductivity meter, HCl, NaOH, Iodine solution, Benedicts solution, balance, pH paper, and thermometer. There is a hot plate and hot water on the side of the room for doing the Benedicts test. A positive reaction for reducing sugars is a green, yellow, or red color. A Biuret’s solution can be made by adding a drop of Benedicts solution and a drop of NaOH to the powder. A positive reaction is a purple color. (You provide your own pen)

Observation Time Please take ~20 minutes to make as many

observations as possible on the powder. 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.

Answering Questions

At this point in a real tournament we would clean up everything, put everything away, and pass out new writing instruments.

We are not going to do that because I need everything out for the next event

You are on your honor.

Question time

Take about 20 minutes to put the question numbers by your observations 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.

Answering Questions

We will be writing the letters of the questions the observations answer in the columns to the right of the observations.

It is best to write the observation’s numbers on the lines after the questions too.

Nowhere do you, or your students ever actually answer the question.

You will not actually use many of your observations.

Scoring the Exam The I and O at the top of the Observation sheet

columns are for Inference and Observation. The scorer would go through and mark one

column or the other for the “observations”. This makes scoring easier

The observations that most completely answer the questions get the most points.

“Observations” that are really inferences receive a maximum of 3 points

Observations written in the second writing instrument receive a maximum of 2 points

Scoring We are now going to look at scoring a sample student’s

paper In reality, a single paper can not be adequately scored. The people who get the 5’s for a given question are the

ones who have the best answers for that competition So an observation that might get a five at the first

invitational of the year, might get a 2 at Nationals. You have to have both the student’s observation sheet

and answer sheet to score. After you have gone through a few papers you will

remember better what the questions are

Scoring The first thing I would like to point out about the

score sheets in front of you is that the partners made 48 observations in 25 minutes???????

The observations are simple and yet redundant Your students need to come in and get right at

making the observations. The students have used every item they were

given to observe multiple times. The students have used presumably every

reagent they were given for observations.

Scoring Are any of the “observations” inferences? The observations keep talking about using 1

ml of the liquid and .15 g of the solid But the student can use the same liquid and

solid for all of the tests. After the temperature, pH, and conductivity of the

1 ml of the liquid is taken If using a well plate students should know what the

volume of the well plate is, so measurement is easy The solid can be added and the tests all retaken.

How did the students do?

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.