P2P Apr 09 Mixing and Kitchen Activities

Blue Licks State Resort Park
14 April 2009
Learning targets
I can observe that when materials change, their mass does not change.
I can show that the mass of something is the sum of the masses of its parts.
I can show that volume is often not conserved when materials are mixed.
I can see that volume may not be conserved because particles of one material
may fit into the spaces between larger particles in another material.
I can observe some properties changing under different conditions
I can observe that some kinds of changes that can occur to materials are
characteristic changes, and can be used to identify the type of material.
Mixing objects
You will be asked to determine the mass and volume of several objects. To
determine the mass of something in this activity, first determine the mass of an
empty graduated cylinder, place the material to measure in the cylinder, then again
measure the mass, and subtract the two for the mass of the object itself.
a) Use a 100 mL graduated cylinder to measure as close as possible 50 mL of
Determine their mass and gently place into a 400 mL beaker.
Use the graduated cylinder again to measure 50 mL of the tiny beads.
Determine the mass of the tiny beads, add to the marbles and swirl to mix.
Pour this mixture back into the graduated cylinder; determine both volume
and mass of the mixture.
For each of the questions below, discuss with your partners, and write
answers in your notebooks.
Is the mass of the mixture equal to the sum of the marbles plus the
Is the volume equal to the sum of the two?
b) Repeat this activity with sand and the beads.
Is the sum of the masses of 50 mL of sand and beads equal to the mass
of the mixture?
Is the sum of the volumes of sand and beads equal to the volume of
the mixture?
c) Repeat this again using sand and water. Be sure to use a very dry
graduated cylinder for measuring the sand
Is the sum of the masses of 50 mL of sand and water equal to the mass
of the mixture?
Is the sum of the volumes of sand and water equal to the volume of
the mixture?
In each of these activities, is mass conserved through mixing?
Is volume conserved through mixing?
Looking at the systems – sand and small spheres, and sand and water, why
do the volumes behave as they do upon mixing?
Check: describe your observations to the instructor, and provide an
explanation for your observations.
Suppose we had done this activity with materials with very similar particle
size, for example salt and sugar. What would you expect the outcome to be,
and why?
Write a rule describing situations in which volumes of mixtures are
conserved following mixing and in which volumes of mixtures are not
d) Now repeat this activity using distilled water and ethanol – measure out
as accurately as you can 50 mL of each, and determine the mass of each. Mix
them in a 400 mL beaker, and swirl to be sure they are well-mixed. Then
pour them back into the graduated cylinder and determine the final mixed
volume and mass.
Is mass conserved? Is volume conserved?
Applying your observation of mixing the large objects, what conclusions can
you reach about the characteristics of water and ethanol?
Check: share your rule with the instructor, and describe your observations
about mixing water and ethanol. What does this say about the properties of
these materials?
The Kitchen Kaper
Chef Emeril was found murdered in his kitchen! He evidently had been preparing
grilled pickles.
The usual suspects were: Wolfgang Puck, Julia Child, Paula Deen, Paul Prudhomme,
Jeff Smith, and Gordon Ramsey.
Each of them had been covered with a mysterious white powder. Surrounding Chef
Emeril were six bags of white powders that the chef had been using in preparation
of the great feast. The powders were labeled with his secret code, so none would
know the details of his special recipes.
The bags’ labels were as follows:
College (this one had been ripped)
Since it was not at all clear what his code meant, it had to be assumed that not all of
the powders were edible, for example they could contain rat poison to keep the
vermin at bay, or plaster to seal up cracks in the walls, so none could be tasted to
determine what they were.
Furthermore, there was considerable evidence of a struggle. Chef Emeril was
attacked by a vicious criminal, and he fought back valiantly. One of the bags had
been ripped open, and its contents evidently had been spilled all over, and it was
quite clear that the perpetrator would have some on his clothes.
The problem is that chefs are always using interesting powders in their cooking so it
is natural that chefs would be covered in whatever they had been preparing.
The task of CSI BlueLicks is to identify the correct criminal using chemical and
physical tests on each of the powders associated with the usual suspects. By
comparing their properties with those of the bags, especially the bag that had been
ripped open, The Culprit would be identified, and could be arrested.
You have seven bags: a bag of “college” and one bag from each of the suspects. To
keep the investigation scientifically controlled and free from bias, these bags have
been numbered, and the actual source will be revealed at the end.
Note: in the following activities, you will be asked to record your observations. If you see
nothing take place, the observation is not “nothing happened”, but rather you need more clarity
and detail, such as – “when the brown drops were added, the color of the sample became a very
light tan. “ The implication of this would be that nothing took place, but this is a conclusion and
not an observation.
Perform the following tests on each of the powders:
1. Observation test. Place a very small amount of each powder onto a dark surface,
such as a piece of black construction paper, and examine with a magnifying glass.
Describe your observations of each powder in your notebooks. Note each aspect of
the powders – relative size, shape of crystals, if appropriate, color, whether they are
homogeneous in appearance, and any other features that might be relevant.
2. Flame test. Place a very small pinch of a powder into the center of a 1”x1”
square of aluminum foil and hold over a candle flame using forceps. Observe
carefully the behavior of the powder over a couple of minutes. Record your
observations in your notebook, including the behavior of the “college” reference
2. Dissolving/phenol red tests. All of your powders should be observed side-byside with this test, including the reference sample. Place a slightly larger pinch of the
powder into a well of the plastic spot plate, and add 1 mL of distilled water. Stir
with the toothpick and observe whether the powder dissolves or not, and record
this. This might be more easily observed against a black backgound. Next, add 2
drops of phenol red solution to each mixture, and observe and record what takes
place. Rinse out the wells with distilled water before proceeding.
3. Acid test. Again, place a pinch of powder into the wells (side-by-side as before)
and now add 1 mL of vinegar to each, and observe and record what occurs. Clean
out the wells before the next step.
4. Iodine test. To a pinch of each powder, add ½ mL of water, stir, then 2 drops of
tincture of iodine. Again, observe and record anything that takes place. Clean up the
wells as before.
Look at all of your data, and decide which powder was identical to the reference
powder found at the crime scene. Since your results will be subject to severe crossexamination by the very well-paid defense team, you need to provide a complete list
of the available evidence arguing in favor of your conclusions. Remember that even
negative evidence is important, as it allows exclusion of certain suspects.