Can't Judge A Powder
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.
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-
- 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?)
- Opaque (solid), translucent(only light passes through), or transparent (clear)?
- How easily it crushes when pressed
- 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)
- How much was given
- pH (See pH section for clarification)
- 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?
- Visible gas?
- Temperature change
Solution of powder and any liquid:
Aqueous solution and any other liquid:
- Temperature change?
If a precipitate forms:
- Supernate? If so, what color, how much?
- What liquid can be added to get rid of the precipitate?
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.
|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.
- The powder dissolves in water.
- The powder is acidic.
- The powder is soluble in HCl.
- The powder conducts electricity when dissolved in water.
- The pH paper becomes amber when dipped into a solution of the powder.
- The conductivity tester lights up when dipped into a solution of the powder.
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:
- Make observations about all of its physical properties.
- 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:
- Takes notes
- Writes answers
- Corrects experimenter on incorrect observations
- Does experiments
- Dictates to Person 1 for both observations and answers
- Gets supplies from director
- Add last minute observations
- Perform 2-person procedures
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.
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
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
- Make observations, not inferences or conclusions.
- 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.
- Remember that density, solubility, and conductivity are all inferences based on something you observe, so write down what you see, not what you infer.
- 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.
- 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.
- Also, it's best if you review/pick up some general (college) chemistry!
- If you want to calculate something (e.g. density), show work on the answer sheet.