Can't Judge A Powder B

[dahagg]

All

I have a question. The suggestion on the wiki is that calculations (e.g., density) be shown on the answer sheet along with the relevant observation(s). It seems to me that calculations are more observation than inference. Therefore, I would want to add an observation that did the calculation to the observation sheet and list that observation on the answer sheet along with the underlying data observation(s). What do you think?

Thanks

Dan

[dholdgreve]

hi, i was wondering how to find volume for this event. thanks

The answer to this question depends largely on what is provided for you to work with... I may mention in the instructions that the substance is being provided in a closed 30 ml container... If I were doing the competition, my first 2 observations would be that the container was approximately 1/2 full, and that the container was approximately 50% full (in case they asked for percentage)... Now, if you were provided a graduated cylinder, or other more accurate ways of measuring, I'd expect slightly different observations. If I were provided both a graduated cylinder and a balance or scale, I would certainly be expecting questions on density, and gear my observations in that direction.

[Tlc3737]

So we did well but I am trying to get better! This is our first time at this event and I have some confusion bc the rules say observations only but then it seems as though they want the team to make an observation that it is acidic, basic, or neutral. Also ionic or covalent. To me those are inferences. I have my team write down pH, the color of pH paper and when asked they write observation numbers for control and aqueous solution but then the next question is is the solution acidic basic or neutral. Help plz!

Also in the rules it is my understanding that the team should only have to answer with the number of the observation yet at an invitation and our region the team was asked to write the observation number and the main point of your observation. At regionals they were told that is what would be used as a tie breaker. I am just so confused.
Thank you

[dholdgreve]

So we did well but I am trying to get better! This is our first time at this event and I have some confusion bc the rules say observations only but then it seems as though they want the team to make an observation that it is acidic, basic, or neutral. Also ionic or covalent. To me those are inferences. I have my team write down pH, the color of pH paper and when asked they write observation numbers for control and aqueous solution but then the next question is is the solution acidic basic or neutral. Help plz!

Also in the rules it is my understanding that the team should only have to answer with the number of the observation yet at an invitation and our region the team was asked to write the observation number and the main point of your observation. At regionals they were told that is what would be used as a tie breaker. I am just so confused.
Thank you

3737,
I feel your pain... We too have been subjected to several "variations" of the rules. Including actually having the E/C provide as many as 15 observations on the observations sheets (pre-printed!)... This is obviously not the way the competition was intended to be run, and ends up strongly favoring the team(s) that actually practiced it that way... Not inferring who they might be... It can be very frustrating to practice, practice, practice the way the rules are actually written, only to go in and find some sort of game that requires the kids to put as their first observation "I have read the rules." before actually starting to do their observations. To this, all can add is to spend a few minutes addressing your kids with a lesson on flexibility... Be ready for anything... What will they do if given a protractor?... red cabbage juice?... Benedict's solution?... Lugol's Solution? What if the test is formatted this way or that? No... you cannot possibly teach every possibility, but rather... teach them to expect the unexpected and above all, don't panic... let the other kids do that... Hope that helps.

To address your other issue, it sometimes is very difficult to achieve "separation" between team scores... I hate to use tie-breakers unless absolutely necessary... might as well start flipping coins. So, to that end, I will throw in a few (sometimes several) questions to, at first glance, appear to be asking for an inference or conclusion... As you pointed out, one good one might be "Was the aqueous substance acidic?" The WRONG answer is "Aqueous solution was acidic." The CORRECT answer would be "Aqueous solution tested 4 on 0-14 pH scale." (NOTE that the question was NOT was the SUBSTANCE Acidic... in that case it would take 2 observations; distilled water observation and the aqueous solution observation, to prove that it was the substance that was acidic, and not the water). This allows the E/C to do the inferring, not the student. Another question such as "Was the Aqueous Solution ionic?" Should actually be answered with 2 separate observations: "CONTROL: Distilled water did not conduct a current." and "Aqueous Solution conducted a strong current." This tells the E/C that there must have been something in the substance that created the ions to allow current to pass, and that it was not there before the substance was added to the water.

One other thought... If you didn't do and observation for a specific question, and need to do a write-in, you are still restricted from inferences, so if asked "was the solution acidic?" and you write in "Yes" that will get you 0 points in my events. If you write in "Aqueous Solution was Acidic." although better, it is still an inference and still lands a goose-egg. The best way to answer that question with a write in is "Aqueous Solution tested 4 with 0-14 pH paper." Any write-in MUST stand alone in sentence format. If I extract what is written in, and read it without first reading the question, is it a complete and independent thought? Write ins like "yes, no, acidic, basic, ionic, blue, conductive..." will never receive any points, even as write ins.

[chem_mom]

Has anyone worked on talc powder? I'm looking for information about the chemical properties of talc. I didn't find anything on the internet and it doesn't seem to react with anything. Thanks!!

[chem_mom]

All

I have a question. The suggestion on the wiki is that calculations (e.g., density) be shown on the answer sheet along with the relevant observation(s). It seems to me that calculations are more observation than inference. Therefore, I would want to add an observation that did the calculation to the observation sheet and list that observation on the answer sheet along with the underlying data observation(s). What do you think?

Thanks

Dan

I would assume that calculations were considered more of inference than observation. What we are doing is recording only the mass and the volume on the observations sheet. We are calculating the density only during the questions part of the test. There is hardly any time to do calculations during the testing/observation part of the event. Just my thoughts.

[chem_mom]

hi, i was wondering how to find volume for this event. thanks

The answer to this question depends largely on what is provided for you to work with... I may mention in the instructions that the substance is being provided in a closed 30 ml container... If I were doing the competition, my first 2 observations would be that the container was approximately 1/2 full, and that the container was approximately 50% full (in case they asked for percentage)... Now, if you were provided a graduated cylinder, or other more accurate ways of measuring, I'd expect slightly different observations. If I were provided both a graduated cylinder and a balance or scale, I would certainly be expecting questions on density, and gear my observations in that direction.

We are having some problems with the density measurement also. We are measuring the volume with a small measuring cylinder but the values we are getting are way off from what is reported on the internet. Also when my students are writing it was greater than 1 because it sank in water they are getting marked wrong.

[chem_mom]

I'm just wondering, but do any of you know what hygroscopic means because it appeared at the invitationals and regionals but I never figured it out. Thanks!

Basically it means that the powder will absorb moisture from its surroundings. Hygroscopic powders tend to clump as a result.

Thank you soooo much! Can you give me an example of a hygroscopic powder?

Brown sugar is a good example of hygroscopic powder.

[dholdgreve]

hi, i was wondering how to find volume for this event. thanks

The answer to this question depends largely on what is provided for you to work with... I may mention in the instructions that the substance is being provided in a closed 30 ml container... If I were doing the competition, my first 2 observations would be that the container was approximately 1/2 full, and that the container was approximately 50% full (in case they asked for percentage)... Now, if you were provided a graduated cylinder, or other more accurate ways of measuring, I'd expect slightly different observations. If I were provided both a graduated cylinder and a balance or scale, I would certainly be expecting questions on density, and gear my observations in that direction.

We are having some problems with the density measurement also. We are measuring the volume with a small measuring cylinder but the values we are getting are way off from what is reported on the interwebs. Also when my students are writing it was greater than 1 because it sank in water they are getting marked wrong.

Stating that the substance had a density greater than 1 is an inference from the observation that it sank... That may be why you are getting it marked wrong... Again, I may ask a question that is easily answered by an inference, but am really looking for the observation that supports the inference. This may seem like a trick question, but if your kids know the difference between an observation and inference, they should be OK... Without a few of those types of questions, it is very difficult to achieve any type of separation in the scoring, and can come down to a massive amount of tie breakers.

Other questions that may be a little deceptive might be:
Is the substance Hygroscopic? (Rather than putting an "observation" that the substance is hygroscopic, I'm looking for "Substance had clumps." It's on the kids to know the definition of Hygroscopic)
Is the Substance Acidic (or Basic) (Rather than putting down an "observation" that states the substance is acid or basic, I'm really looking for a pH test result)
Is the substance ionic? (Rather than list "Substance is ionic" as an "observation," I'm looking for a quantitative statement of conductivity. I expect the kids to know that this is the observation needed to determine if the substance is ionic)

This is really hair splitting, but something worth discussing with your kids... In theory, there is a distinction between soluble and dissolve... Soluble chemicals will ionize in solution (think salt)... Substances can "dissolve" but not ionize (think sugar). The only way to tell whether the substance has dissolved or become soluble is to do a conductivity test. If your test is negative for conductivity, a determination needs to be made to determine if there is less solid in the aqueous solution than before the water was added... I really don't know how many E/Cs make this distinction however.

[asthedeer]

And I get the privilage of using this awesome creatively made machine!

Just some suggestions for you all that are building your conductivity testers:

I went to the craft store and picked up a little wooden box with a hinged lid and a latch, and drilled some holes in the top and side. I taped the battery to the inside of the box, and glued the LED to a hole in the top (which let the leads through) and all the messy resistor + wiring and stuff is contained inside the box. Some longer wires protrude out the side of the box, and voila, a very concise, neat box with a switch (I decided to include one for safety measures to protect the LED), an LED, and some wires.