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Can't Judge A Powder

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Can't Judge a Powder is a chemistry event in which the goal is to teach competitors about the importance of observation of many things in a short period of time. Normally you get 25-35 minutes of using different substances to observe the reaction of the powder that the event coordinator provides. At the 2024 National Tournament, teams were given 25 minutes to observe, and then the rest of the time to take the test/clean up.

What to Observe

For everything that is given, once you think you are finished with it, think to yourself "Is there anything else I could possibly write down?". For instance, when HCl is added to the powder, do you hear a sound? Do bubbles appear? Is there an odor? How much did you add? Was the HCl bottle numbered? On the last two Nationals tests, they have asked what number was on the bag the powder was in, so no observation is too obscure to be asked. In addition, think about what the supervisors will very likely ask. If they specifically give you a demo or special experiment, it is very likely that there will be a question on it. If you are short on time, only write down the basics for each step. If you have excess time, write down every little thing. Here is a general list of what are possible things to write down for each step-

Powder:

  • Luster
  • Size of individual particles
  • State of Matter [Crystals (i.e. sugar), Grains (i.e. yeast), or no defined shape (i.e. flour)?]
  • Texture (i.e. Clumpy?)
  • Color
  • Opaque (solid), translucent(only light passes through), or transparent (clear)?
  • How easily it crushes when pressed
  • Odor
  • How much was given total
  • Type of container it was given in
  • Weight of powder sample, and how much was weighed (you will also need to take a control weight of the beaker without the powder)

Any Liquid:

  • How much was given
  • Color
  • pH (See pH section for clarification)
  • Odor
  • Temperature
  • Conductivity
  • Weight of liquid, and how much was weighed (you will also need to take a control weight of the beaker without the liquid)

Adding powder to any liquid:

  • Dissolves? How much, how quickly, how easily?
  • Odor
  • Bubbles?
  • Sound?
  • Visible gas?
  • Temperature change

Solution of powder and any liquid:

  • pH
  • Color
  • Conductivity
  • Opacity

Aqueous solution and any other liquid:

*The aqueous solution is just ___ grams of powder + ___ mL water

  • Precipitate?
  • Temperature change?
  • Color
  • pH
  • Conductivity

If a precipitate forms:

  • Color
  • Opacity
  • Supernate? If so, what color, how much?
  • What liquid can be added to get rid of the precipitate?

Sometimes, you can also get special tools such as a scale, heating apparatus, or special scientific equipment:

  • In this case, make sure to weigh all given substances and make observations about the substance itself, or in some cases, if given Benedict's solution or something similar, make sure to test the aqueous solution instead

Observation Quality

The quality of observations will make a big difference at more competitive tournaments, especially, ones where the test is harder, the observation quality is of utmost importance and gets you points. When making observations, you should write them such that the person reading your observations should be able to answer the questions using their chemistry knowledge, without actually having to do the physical testing during the lab portion of the test. Make sure to keep it short, sweet, and simple, but also make sure to have all the important information for time's sake. For example:

  • Instead of saying "The temperature is 20.", say "After thermometer in contact w/ water for 10 secs, temp = 20.53° C."
  • Instead of saying "pH = 1", say "after 10 secs contact w/ HCl for 10 secs, pH strip turned red, so pH = 2"

Now, if we had more solutions, we would probably have to shorten it a bit and instead of writing "after ___ in contact for 10 secs" for all of those observations, I would recommend to add an extra few observations at the top to look something like this:

  1. ⭐ Water observations
  2. 1.5 mL water used
  3. Instrument in contact w/ water for 10 secs
  4. Etc.

Observations versus Inferences

An observation is the gathering of information by using our five senses: sight, smell, hearing, taste, and touch. There are two types of observations, qualitative and quantitative. Qualitative observations describe what we observe, such as "the sky is blue." Quantitative observations measure what we observe, using numbers, such as "the flower has seven petals." Both types of observations are necessary for this event.

An inference is an explanation for the observation that you have made. They are based on previous experiences and prior knowledge. While these are important, during a competition you only want to make observations in order to receive the most credit for you answers.

Please note that this table only shows the ideas behind observations and inferences. The wording of the phrases is made simple to get the point across, but these observations are not quality, and would not receive a 5 on a test.

Observation vs. Inference
Observation Inference
The powder clumps The powder is hygroscopic
The powder has a pH of 5 (See pH section for clarification) The powder is acidic
The solution of the powder conducts The solution of the powder has free ions
The powder dissolves The powder is soluble
20 mL of the powder weighs 30 grams The powder has a density of 1.5 g/cm3


Practice: Label each of the following observation or inference.

  1. The powder dissolves in water.
  2. The powder is acidic.
  3. The powder is soluble in HCl.
  4. The powder conducts electricity when dissolved in water.
  5. The pH paper becomes amber when dipped into a solution of the powder.
  6. The conductivity tester lights up when dipped into a solution of the powder.


A great way to remember if something is an observation or an inference is to ask yourself, "If I knew nothing, could I have wrote this using my 5 senses and kit?"

At the Competition

This is an event where you are required to make a large number of observations about a sample in a short period of time. The best way to do this effectively is to have a system that you use every time you practice and compete so that you are able to work quickly. You will almost definitely have only 1 pen for each section, so get used to having one person do tests and the other write down observations. If you are using enough detail in your observations, that person writing will likely be significantly slower than the person doing the tests with the powder.

An example of a process is this:

Person 1-

  • Make observations about all of its physical properties.

Person 2-

  • Start by taking the mass of a beaker (or other measuring device), alone, if you are given a balance.
  • Using the same beaker (measuring device), take the mass of the a certain amount of the powder (be sure to record this).
    • i.e.[20 ml of the powder in the beaker weighs 500 g]

(After both are done) One person could write while the other is performing tests-

  • Distilled water alone
  • Powder and distilled water
  • HCl alone
  • Powder and HCl
  • NaOH alone
  • Powder and NaOH
  • Finish with whatever else they have you doing; it could be another solution to test with, or it could be certain experiments that you have to do.

Another very general one that got two teams first place at a Regional:

Person 1:

  • Takes notes
  • Writes answers
  • Corrects experimenter on incorrect observations

Person 2:

  • Does experiments
  • Dictates to Person 1 for both observations and answers
  • Gets supplies from director

Both:

  • Add last minute observations
  • Perform 2-person procedures

The Test

When taking the test, it's very important to pace yourself, and make sure to split it up with your partner, but in a different way. CJAP tests are generally designed not for you to answer the question, but to USE YOUR OBSERVATIONS TO ANSWER THE QUESTION. It is very important NOT TO ANSWER THE QUESTION though! DO NOT ANSWER THE QUESTION BY ITSELF, ANSWER ONLY USING OBSERVATION NUMBERS - that is unless the test specifies!!! Strategies for the test vary from team to team, but the one method that seems to work best is one partner (that has a good level of knowledge of chemistry) should translate the question into what observations should be used to answer the question, which the other partner (who has good logic and reasoning skills) should find the observations, and help make any late observations if necessary.

pH

According to a 2010 rules clarification, pH is an observation, not an inference. However, to receive the full 5 points, both the color of the pH strip and the actual pH need to be recorded. i.e. "The pH of the aqueous solution of the powder was 7, turning the pH paper yellow." However, your event supervisor may not be aware of this decision on scoring and may think it is an inference, so it is best to ask the event supervisor beforehand or at the competition to make sure you know their stance on this.

Conductivity Tester

It is fairly easy to make a conductivity tester. All you need is:

  • A 9 volt battery
  • A NineVolt battery connector
  • A Resistor(330 ohm, 1/4 watt)
  • A LED
  • Wire

No 120V conductivity testers will be allowed.

All of this should be easy to get at a local hardware store or Radio Shack Next we have to do the very simple wiring. Take the red lead of the Nine Volt Battery connector and solder/wrap/conductive glue to one end of the resistor. To the other end of the resister attach another wire that has its other end bare. Now take your LED and look at the two lead coming out of the bottom. The shorter one is the negative lead and the longer one is the positive lead. Take the positive lead and attach a wire with its opposite end bare. To the negative lead, attach a wire connecting it to the negative wire from the 9V battery. If you do not use a resistor you risk burning out your LED.


In the end it should look like this:

Tips about making Observations

  1. Make observations, not inferences or conclusions.
  2. Write down anything you see, whether it be a color change, or just that the HCl is 1M. The test can technically have questions about anything given to you, so even though making these observations may seem stupid, the more you write down, the more you will have to do the test with.
  3. Remember that density, solubility, and conductivity are all inferences based on something you observe, so write down what you see, not what you infer.
  4. Control observations are very important and appear on many tests. These can be anything from the amount of a substance given to its color, and are a good way to find out who actually knows what the event is about.
  5. Look at any tests you can find! The 2003, 2004, 2005, 2007, and 2011 test booklets will all have past Nationals tests, and the 2010 test exchange even more Regional and Invitational tests. Even if you don't take the tests, you can read the questions and get more ideas of what to record.
  6. Also, it's best if you review/pick up some general (college) chemistry!
  7. If you want to calculate something (e.g. density), show work on the answer sheet.

Links and Files

Can't Judge a Powder Coaches Clinic Presentation‎

Smorgan6's notes

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