Lab 2 – A Rocky Problem (Behavior of Matter)
Can you tell the difference between a rock and a shell? Sounds like a very
simple question, doesn’t it? But is it really so simple? Sometimes very difficult
ideas hide behind simple sounding questions. Let’s see if that is happening here.
Activity A As directed, get a bag of rocks and a bag of shells from the
supply area and take them to your lab table. Pour the contents of each
bag onto a paper towel. Separate the objects into two piles; rocks in
one and shells in the other.
Question 1. Do all the shells look exactly alike?
Question 2. Do all the rocks look exactly alike?
Question 3. How did you decide which were rocks?
Question 4. How did you decide which were shells?
Well, that shouldn’t have been too tough. The color, shape and feel of
rocks are very different from those of shells. You can tell them apart at a glance.
But suppose some of these features of rocks and shells that are easy to notice
were changed. Could you still tell them apart? Let’s see.
STOP & Pause here.
Some rocks and shells like those you have been sorting have been ground
to powder. Rock and shell powders have been kept separate. They are in four
numbered bottles at the supply area. Each bottle contains either rock or shell,
but not both.
Activity B Obtain 4 pieces of round filter paper. Along the edge, label
them 1, 2, 3, and 4. Measure a small amount of powder from each
bottle using its spoon and place the sample on the corresponding
number round filter paper. Don’t mix up the spoons. And don’t mix the
samples of powders in the bottles. Replace the lids correctly on their
numbered bottles.
Now you’re ready to try some detective work. Find out which of the
samples is ground up rock and which is ground up shell. You might want to use
a magnifying glass (found in the supply area) to compare whole pieces of rock
and shell with the ground up pieces. It might also be helpful to make
observations that do not require use of equipment, like smelling and feeling. You
will need to observe the materials carefully. Your observations should allow you
to describe how the sample looks, feels, smells, etc. Create a Table of
Observations in your notebook (as shown below) to record your observations.
Be sure to include your observations of the whole rocks and shells. Even a
negative observation, such as No odor, can be important.
Table of Observations
Materials
Whole Rocks
Observations
Whole Shells
Ground up Sample 1
Ground up Sample 2
Ground up Sample 3
Ground up Sample 4
Question 5. Based on your observations…
a. what do you think Sample 1 contains; rock or shell?
b. what do you think Sample 2 contains; rock or shell?
c. what do you think Sample 3 contains; rock or shell?
d. what do you think Sample 4 contains; rock or shell?
Following your detective work, could you decide which bottles contain rock
and which contain shell? Why or why not?
STOP here for today. Follow directions for clean up.
Today you will do another activity that may help you decide which bottles
contain rock and which contain shell. At the supply area, you will find a dropper
bottle of liquid labeled HCl. This substance is hydrochloric acid. You will use it
in this next activity. But before doing so, read the following safety note carefully.
Safety Note
Use extra care when working with lab chemicals. Some can burn your skin
or stain your clothing. Wipe up spilled chemicals quickly, washing the spill area
with plenty of water. And make it a habit of cleaning your equipment and work
area regularly with damp paper towels.
Don’t breathe chemical fumes unless told to do so. Be extra careful with all
acids. Some acids should not be taken to your work area. You will use them at
special locations in the room.
Wear safety glasses to protect your eyes from flying objects or splashed
chemicals. Watch out for yourself and others around you. And always report
accidents immediately to your teacher!
Don’t misbehave in a science lab. It is a dangerous thing to do so. Don’t
take chances and don’t let your classmates take them either.
Activity C Put a whole shell onto a clean dry paper towel. Get the HCl
from the supply area. Put 2 drops of HCl on the shell (from above
without touching the shell). Return the dropper to the bottle. Observe
the shell for a minute or so. Then rinse the shell with water (at the
nearest sink) and return it to the pile. Do this with several different
shells.
Question 6. What happened when you put HCl on the shell?
Question 7. Did all the shells you tested behave the same way?
Repeat Activity C using rocks instead of shells.
Question 8. Did anything happen when HCl was put on rock?
Question 9. Did all the rocks tested behave the same way?
Question 10. How could you use this HCl test to tell whether the
powdered materials are rocks or shells?
Check your answer to question 10 by doing to each sample the things you
suggested in your answer. The samples should be placed on the clean dry round
filter paper before experimenting on them. Be sure to observe carefully what
happens in each case. Create a Table in your notebook (as shown below) to
record your observations.
Table of Observations Using HCl Test
Materials
Ground up
Sample 1
Ground up
Sample 2
Ground up
Sample 3
Ground up
Sample 4
Observations
Now use the HCL test observations you recorded in the Table to decide what
each sample contains. Do this by writing either Rocks, Shells or Can’t decide to
your answers for question 11 below.
Question 11. The HCl test suggests that the samples are as follows:
a. Sample 1 contains…
b. Sample 2 contains…
c. Sample 3 contains…
d. Sample 4 contains…
Question 12. There are several detective methods like sight, smell,
taste, etc. Which is the surest way to tell ground up rocks from ground
up shells?
Question 13. You have tested a few rocks. Can you say that all rocks
would behave the same way if HCl were added to them?
Question 14. Can you say that all shells would behave the same way if
HCl were added to them?
So far, you have found that shells fizz when HCl is put on them. Most rocks seem
to be different from shells. They don’t fizz.
Question 15. Suppose a rock had some shell material in it. Would you
expect it to fizz if HCl were added to it? Why or why not? Explain your
answer.
Why are rocks and shells so different? Is it because they are made of different
kinds of “stuff”? is it because the stuff is put together in different ways? Or is it
both of these? Those questions ask you to do some explaining. They ask you to
use your imagination. They ask you to build a mental model about rocks and
shells.
Question 16. Why, then, do you think rocks and shells behave
differently?
Matter is the scientific word for the “stuff” of which everything is made.
There is a scientific mental model called the particle model for matter that states
all matter is made of tiny moving particles. Have you heard of atoms or of
molecules? These particles (parts) are part of that model.
Question 17. Why did shells fizz and rocks not fizz when HCl was added
to them? Use the idea of particles to answer this question.
That was not an easy question at all. Just accepting the idea that matter is made
of particles does not help you explain very much. It doesn’t help you explain why
the bubbling occurs, or why it doesn’t occur. You must know a great deal more
about matter before you can explain its behavior. You need a more complete
model for matter. Assuming that all matter is composed of particles is a useful
idea. But it is not useful enough. We must develop a useful particle model for
matter. How? We might try to describe what the differences are in matter. Then
we could try to find out if there is a different kind of particle for each kind of
matter. We might also try to find out if all matter is made of only one kind of
particle. If we find evidence for more than one kind, we’ll want to know how
many there are.
Question 18. Which assumption is more reasonable?
a. All matter is made of one kind of particle
b. Matter is made of more than one kind of particle.
Write the more reasonable assumption in your notebook.
During the chemistry unit, you will be conducting experiments to develop, test
and improve the model for matter and try to find out how matter is held
together.
Clean Up Now that you have finished all lab work, clean and put away your
equipment in the supply area as directed. Specifically,
1. Rinse and dry all rocks and shells that were tested. Place them back in
their storage bags and return them to the supply area.
2. Return HCl dropper bottles to the fume hood.
3. Discard all used filter papers and paper towels in the trash.
4. Wipe down lab tables with damp paper towels and discard in the trash.
5. Ensure that all powder container lids are tightly closed and spoons are
correctly attached to avoid contamination.
6. Return safety glasses to the cabinet and fold away aprons.
7. Wash hands with soap and water at any of the four sinks.
STOP here for today.