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Determination of a Chemical Formula

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					                         Did I just Find Treasure?
                                                         Initial volume =   _____


Essential Question: How do the differences in matter contribute to our
daily lives?
Enduring Understanding: Each element has its own unique chemical and
physical properties allowing mankind to create an almost endless
combination of materials.
Goal: You will correctly identify an unknown substance using its physical
properties
Role: An observant student walking down the street
Audience: Yourself

Situation: On your way home from school one day, something on the ground
catches your eye. You pick up a ring that is lying amongst some trash on
the sidewalk. The actual ring part and the setting are pretty bent up,
but it has a HUGE, beautiful, clear stone. Did you just find a piece of
treasure lying in the street? Could this be a diamond ring? If so the
stone would be worth a lot of money. Of course it could also be a
complete fake. You don’t have the money to take it to a jeweler and have
it appraised. Besides, what if they lie to you and tell you it is
worthless so you will leave it with them and then cash it in for
themselves? How can you determine what the stone is?
Performance: As you are a devoted student of Chemistry, you know that each
substance has it’s own chemical and physical properties that can be used
to identify it. You decide to use the same approach from several labs and
calculate the density of the stone since it is falling out of the setting
already.

First you decide to do a little research about diamonds and fake diamonds.
Obviously diamonds are very expensive and make for the most expensive
jewelry. But there are several different types of “fake diamonds”, and
some are cheaper than others. That seems to complicate matters. If you
don’t have a diamond, the next best thing to find would be a cubic
zirconia, which is very clear and bright, but not as hard or expensive as
diamonds. Some cheap jewelry uses clear glass instead as it is a
relatively cheap substance. The cheapest stuff though uses plastic you
discover. Plastic!

You decide that the best physical property to use to determine the
identity of your stone is the density. You use the Internet to find the
densities of each of the possible substance and are happy to see that the
densities are far apart from each other, meaning it is a good way to see
what the stone is made of. You record your density values for the
substances here:

                         Substance     Density (g/ml)
                     Plastic
                     Glass
                     Diamond
                     Cubic Zirconia

From your reading of Archimedes and your density lab using candy bars, you
know how to take the measurements needed to calculate the density of an
object. You will need the volume and the mass. The volume can be
calculated using volume displacement in a graduated cylinder and the mass
can be measured using a triple beam balance.
You decide to measure the mass first so you don’t have to worry about
weighing any water from the volume measurement. Below is an image of the
triple beam balance. Record the mass of the stone on the line below:



Mass = ___________________

You remember that to measure the volume of an object in a graduated
cylinder, you have to have some water in the graduated cylinder already
and measure that volume first. Then you put your stone in the cylinder
and see how much the volume changed. Below is the image of the graduated
cylinder after adding your stone. Your initial volume in the graduated
cylinder is _________________. Record the volume of water and the stone
on the line below:


Volume of water & stone: _______________
Now you have everything you need to solve your mystery. Use the space
below to calculate the volume of your stone and then the density. Make
sure you use the correct units to go with your answer:


Volume of Stone: ______________________
Calculation:




Density of Stone: _______________________
Calculation:




Now the mystery is solved!!! Write a paragraph that states which
substance your stone is made out of and how you know this to be true. Use
your calculations and knowledge of physical properties to justify your
answer. In your answer be sure to answer the following questions:
   Can two substances have identical densities?
   Can the density of a substance change?
   Why is density considered to be a physical property?
   Would your results change if you found out that the balance was
     reading 1 g too heavy? How so?

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                                                                         Assessment Rubric
Subject: Chemistry I
GRASP: Did I Just Find Treasure?
Standards:
C.2.1 Investigate and classify properties of matter, including density, melting point, boiling point, and
solubility.

C.2.2. Determine the definitions of and use properties such as mass, volume, temperature, density, melting point, boiling point, conductivity, solubility, and color
to differentiate between types of matter.

Score:               4 (advanced)                         3 (proficient)                    2 (approaches proficient)                1 (does not meet)
Concept              The explanation shows a complete     The argument shows a              The argument only shows some             The argument shows no
                     understanding of the density         substantial understanding of      understanding of the density concept     understanding of the density concept
                     concept and physical properties,     the density concept and           and physical properties, and their use   and physical properties, and their use
                     and their use in this comparison     physical properties, and their    in this comparison problem.              in this comparison problem.
                     problem.                             use in this comparison
                                                          problem.
Calculations         Each step of the procedure is        Each step of the procedure is     Each step of the procedure is            Each step of the procedure is
                     calculated correctly 100% of the     calculated correctly 70% of the   calculated correctly 50% of the time.    calculated correctly less than 50% of
                     time. All data tables are properly   time. All data tables are         Not all of the data tables are           the time. Not all of the data tables
                     completed with units.                properly completed but            completed or are missing all units.      are completed and are missing all
                                                          missing some units.                                                        units.
Language             Provides a well organized and        Provides an organized and         Argument fails to follow an organized    No argument provided and substance
                     logical argument using evidence      logical argument using some       structure, barely uses any evidence,     not identified. Grammar mistakes
                     from the calculations, and proper    evidence from the calculations,   and has frequent grammar mistakes        impact ability to understand meaning.
                     chemical vocabulary and              and mostly proper chemical        and lack of chemical vocabulary.
                     grammar.                             vocabulary and grammar, but
                                                          misses the opportunity to
                                                          strengthen the argument
                                                          through detailed use of
                                                          evidence from the calculations.
Neatness and         The work is presented in a neat,     The work is presented in an       The work appears sloppy and              It is not possible to grade project
Organization         clear, organized fashion that is     organized fashion that may be     unorganized. It is hard to know what     because of organization of project.
                     easy to read.                        hard to read at times but         information goes together.
                                                          makes obvious what
                                                          information goes together.

				
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posted:7/5/2011
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