Instructor’s Notes for #13 Keep em Separated
Instructional Video = https://youtu.be/WqXaIs9Bmfg
THE INSTRUCTIONAL VIDEO demonstrates:
A “small scoop”
Safe Heating of disposable test tubes
Hot tube in plastic rack = melt!
Reservoir of disposable tubes
Weighing from buffet table—transport the bottle to the scale!
Heating a beaker over burner using beaker tongs
Disposal procedures—black tubes vs. white tubes
Don’t heat dry powders in a beaker!
Shows how to heat small samples of liquids in disposable test tubes
Note: STUDENTS SEEM INCAPABLE OF ANTICIPATING THAT
HEATING SUGAR IN A BEAKER WILL MAKE THE BEAKER
CHAR. NEED TO MONITOR STUDENTS DURING THE FREEFORM EXPERIMENTAL PHASE.
INSTRUCTOR SHOULD PICK UP ALL THE
EVAPORATING DISHES PRIOR TO LAB!
Set-up requires
 2-liters of 2 M HCl (diluted pool acid is recommended!)
 Powder A = powdered sugar
 Powder B = powdered chalk
 Disposable test tubes (large box on buffet table—students take as needed)
 Mixture of powdered sugar and chalk—save this in reserve until students reach the stage
of separation.
Assignment #13: Keep ‘em Separated Lab
Overview: In today’s experiments, you will work with two white powders. One of the powders will be
powdered sugar. The other will be powdered chalk. Chalk is made of calcium carbonate (you should be
able to write its chemical formula!). Powdered sugar is an organic molecule with the formula C12H22O11.
You will be instructed to do three tests on each powder. From the results of these tests, you will attempt
to find a way to SEPARATE a mixture of chalk and sugar so that you have a sample of pure powdered
sugar or pure powdered chalk. If you find a separation method that seems to work, you will then need to
run tests on your isolated powder to prove what it is (and whether it is truly pure).
Step #0: Safety First!
Before starting any experiments, please put on a pair of safety glasses and proper shoes!
Test #1: Heat Stability
(10 minutes recommended)
Note 1: for these tests, try to heat gently--don't "burn to a crisp ". If you see smoke emerging from your
test tube, you should STOP heating!
Note 2: “Nothing happened” is NOT an observation—describe what you saw using precise language!
A. Place a small scoop of powder A in a disposable test tube and heat over a modest Bunsen burner
flame. Record observations of any changes that occur. Rest your hot tube in a dry beaker to cool.
B. Place a small scoop of powder B in a disposable test tube and heat over a modest Bunsen burner
flame. Record observations. Rest your hot tube in a dry beaker.
Questions for Thought (attempt to answer these questions in your write-up!):

Equations for the thermal decomposition of sugar and calcium carbonate are shown below.
Do your test tubes provide convincing evidence that these reactions have occurred?
o
C12H22O11  12 C (s) + 11 H2O (g)
o
CaCO3 (s)  CaO (s) + CO2 (g)
Test #2: Reactions with Acid
(15 minutes recommended)
A. Use weighing paper to measure out between 0.40 and 0.60 grams of powder A into a clean test tube.
While holding the tube with a test tube clamp, add 10 mL of 2-molar HCl to the test tube. Record
observations.
B. Do the same experiment with 0.40 to 0.60 grams of powder B in a separate test tube. Record
observations.
Questions for Thought (attempt to answer these in your write-up!):


Reacting chalk with acid can produce a liquid that appears “carbonated”. Do you think there
is a connection between the word “carbonation” and calcium carbonate?
Can the acid test be used to conclusively identify sugar or chalk?
Test #3: Solubility in Water
(15 minutes recommended)
A. Measure out approximately 0.5 grams of powder A (that means a mass between 0.45
and 0.55 grams) into a medium-sized beaker. Add 25 mL of distilled water and stir with
a glass rod. Record observations. Then WARM the beaker over a BUNSEN BURNER to see
whether any changes occur. If the liquid begins to boil, you should cease heating. Note:
This test is designed to assess the SOLUBILITY of powder A in both cold and hot water.
B. Do the same experiments with powder B in a second beaker. Record observations.
Question for Thought: Discuss why heating Powder A in water does not result in the
same color change observed when heating dry Powder A.
Continued on the next page
Assignment #13: Keep ‘em Separated Lab (continued)
Test #4: Unscripted Separation Attempts (20 minutes recommended)
You should now have a discussion with your lab partners about strategies you could use to accomplish
the goal of separating a mixture of sugar and the chalk. Your goal is to take a mixture of the two
powders (provided in a bottle labeled “Mixture”) and end up with chalk and sugar in separate vessels.
In any unscripted experiment, you should start by having a group brain-storming session. Try to
conceive of various possible methods and discuss how/why each method could work (or could fail). The
more precise your thinking is originally, the less time you will waste in unproductive pursuits.
If you have multiple ideas in your group, it is good to try out all of the ideas. Use the power of the
team so that each member contributes to setting up the experiment and thoughtfully analyzing the results.
To run a separation experiment, follow the brief guidelines shown below:
 You should begin with 0.80 to 1.00 gram of the powder labeled “Mixture”. This mixture
contains both powdered sugar and powdered chalk.
 Run your experiment while recording your METHODS AND OBSERVATIONS in detail.
 Do not heat a DRY POWDER in a beaker or evaporating dish! You may heat a dry powder
only in a disposable test tube.
 Do not evaporate a liquid to DRYNESS in a beaker or evaporating dish! You may evaporate
1 or 2 mL of a liquid to dryness in a disposable test tube.
 If you think you have successfully separated the powders, TEST THE PURITY of your
separated powders using appropriate methods. Note: this is a very important test—you want
to provide convincing evidence that no sugar remains in your chalk sample (and vice-versa).
 Note: any heating of dry samples should be done in a DISPOSABLE test tube!
ADD PHOTOS OF HEATING GUIDELINES!!!!! Warming an aqueous solution = OK in any vessel.
Evaporating an aqueous solution requires disposable test tube (1 mL volume of liquid). Heating a dry
powder may be done only in test tube.
Write-up Guidelines are on the next page.
Assignment #13: Keep ‘em Separated Lab (continued)
Write up guidelines
For this lab, you will make a paragraph-based write-up on your own paper. You may type or
hand-write your lab. Pictures (either hand-drawn or photos) are appreciated!
Guidelines for success are provided below:
A lab write-up should always begin with a thoughtful INTRODUCTION. Some example introductory
paragraphs are shown below. Please choose one of these as a template for your write-up and flesh out the
skeleton with your own personalized information.
Introduction suggestion A
In this lab, we investigated the chemical and physical properties of __________ and
___________. Although these two powders looked very similar, they did not react in similar
ways. We then exploited the difference in their _____________________ (choose specific
chemistry word/s) to attempt a separation of the two powders. Our purity tests at the end of the
lab suggested ________________________(say something about how successful your
separation was—if you didn’t do any purity tests, state this clearly instead of pretending you did).
Introduction suggestion B (will probably require a little internet research)
Chemists are often employed to separate mixtures. Many useful elements and compounds occur
in nature, but they are very rarely found in a pure state. For example, _________________ (you
choose a useful element or compound) is found in nature as ______________________ (some
sort of mixture). Chemists may utilize a number of clever strategies to separate one component
from another. In this lab, we separated a mixture of chalk and sugar based on their different
_____________________.
For the SCRIPTED SECTION of your write-up provide a data table to describe what you learned in tests
#1-3 (Heat stability, reactions with acid, water solubility). Format your table as follows:
Test
What did you do?
(one sentence summary)
What happened?
(observed outcomes—
one sentence summary)
What do the results
mean?
(one sentence
summary)
1A
1B
2A
2B
3A
3B
You may include a discussion of ONE of the Questions for Thought in your write-up. Do this only if you
feel you have a meaningful answer to the question.
For Test #4 (the unscripted separation experiments), no specific instructions were provided. You
should start by discussing your IDEAS (i.e. why you chose the methods you did). Then you must
DESCRIBE TO YOUR INSTRUCTOR WHAT YOU DID! Be thoughtful when you describe your OBSERVATIONS,
and explain what you think was happening chemically that resulted in these observations. Include
photographic evidence to support your claims. If you performed experiments to determine the purity of
your separated powder(s), describe your methods, the observed results, and the meaning of these results.
IT IS ESSENTIAL THAT YOU TELL THE TRUTH ABOUT WHAT YOU DID—ENGAGING IN
WISHFUL THINKING IS BADDDD SCIENCE!