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Crystals
Conduct observations of the physical
properties of crystals.
Dissolve and recrystallize materials.
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Objectives
Develop an understanding of the meaning of characteristic
properties of substances by testing and comparing different
household crystals.
Recognize that solubility is a characteristic property of a
substance.
Identify an unknown crystal by comparing its characteristic
physical properties with those of four known crystals.
Measure equal amounts of crystals by mass rather than volume.
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Investigation Questions
Can you identify an unknown crystal by comparing its appearance
to other known crystals?
Can you identify the unknown crystal by crushing the different
crystals and comparing them?
Do some of the crystals dissolve more or less than others?
What is the best way to measure equal amounts of crystals?
Can you identify the unknown crystal by the amount that dissolves
in water?
Can you identify the unknown crystal by the way it looks when it
recrystallizes?
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Key Vocabulary
MassVolumeDensityPhysical PropertyDissolveCrystallizeSolubility-
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Key Vocabulary
Mass- The amount of matter. The weight of an object (on Earth.)
Volume- The amount of space that matter occupies.
Density- The amount of matter in a cubic centimeter.
Physical Property- Observable properties of matter
Dissolve- To break up. To put into a liquid solution.
Crystallize- To form a solid crystal.
Solubility- A materials ability to be dissolved.
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Part 1
Describe the Characteristics of 4 Crystals
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Materials
Sodium Chloride (Table Salt)
Magnesium Sulfate (Epsom Salt)
Calcium Chloride (Road Salt)
Sucrose (Sugar)
Black construction paper, 1/2 piece
Magnifying glass
Labels
Plastic Spoon
Tray
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Procedure

Follow the procedure found on page 1 of student handout 2.1.

Write the observable characteristics of the crystals when
viewed under magnification.

Make a class list of the characteristics.
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Observation:
Characteristics of Each Crystal
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Part 2: Crushability
After observing physical characteristics of each crystal, crush the
crystals and compare their “crushability.”
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Scientific Background
Like rocks, crystals are composed of minerals. One of the
scientific tests used to compare rocks and crystals is a
hardness test. The most common test of hardness is called the
Rockwell test. Using the Rockwell test, scientists determine
how much force it takes to make an indentation and to crush a
crystal. The crystal is given a number from 1 to 10, with 10
being the hardest material.
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Investigation Question

Can you use a “crushability” test to compare the unknown
crystal to the other crystals?
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Materials
Sodium Chloride (Table Salt)
Magnesium Sulfate (Epsom Salt)
Calcium Chloride (Road Salt)
Sucrose (Sugar)
Black construction paper, 1/2 piece
Magnifying glass
Labels
Plastic Spoon
Paper Cups
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Procedure

Put your thumb in the spoon.

Using the same amount of force, crush each crystal.

When crushing each crystal, pay attention to how much force
it takes to crush the crystal, the sound the crystal makes
when it is crushed, and the residue (what is left) of each
crystal.
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Observations and Conclusions

Complete student worksheet 2.2
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Part 3: Dissolving
Use the solubility of each crystal to compare the crystals to an
unknown.
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The Science of Solubility
Tests of solubility measure the maximum amount of a solute
that can be dissolved in a solvent. For example, how much salt
(solute) can be dissolved in water (solvent.)
Some solvents, like acids, are better at dissolving a solute.
Some solutes, like ethyl alcohol, are easier to dissolve in any
solute.
Water is called “The Universal Solvent” because water is
everywhere and most solutes will dissolve at least a little bit
over time in water.
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Which material do you think would
have greater solubility?
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Investigation Question

Can you compare the unknown material to the other
materials by comparing their solubility?
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Materials
Table Salt
Epsom Salt
Road Salt
Sugar
Unknown Crystal
5 Clear Plastic Cups
5 Paper Cups
Spoon
Warm Water
Scales
Marker or Pen
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Procedure

Label each cup with the crystal that will be dissolved into it.
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Weigh 5g of each crushed crystal in a paper cup.
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Measure 1teaspoon of warm tap water into each cup.
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At the same time and with the same amount of energy, use the
spoon to swirl each solution for 20 seconds. Allow undisolved
crystals to precipitate to the bottom.
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Pour the solution back into it’s paper cup. Be careful not to pour
out undissolved crystals.
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Compare the amount of undissolved crystals in each cup.
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Repeat 2 more times.
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Observations and Conclusions
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Record observations using 2.3 Solubility Test
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Part 4: Crystallization
Observe the recrystallization of each solute. Compare the
appearance of the unknown material with each material .
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Scientific Background

Because of it’s characteristic properties, every solid
crystallizes in a unique way.
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Crystals are generally formed when the solvent (liquid)
evaporates leaving the solute (solid.)
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How did these crystals form?
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Investigation Question
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Can you identify the unknown crystal by comparing its
appearance to the other materials when it crystallizes?
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Materials
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Magnifying Glass
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Wells containing samples of each solution from part 3.
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Procedure

Observe each crystallized solute to compare their
characteristics.
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Observation and Conclusion

Complete 2.4 Recrystallization Test
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Read and complete the Review and Apply Worksheet
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Read and complete Think About It
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Mixtures and Solutions
Mixtures and solutions are both combinations of 2 or more
substances.
Mixtures can be separated with a filter, solutions can only be
separated using evaporation.
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Vocabulary
SolutionMixture-
SuspensionDissolveFilterEvaporate-
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Key Questions
When 2 substances (charcoal and salt) are mixed into water,
can those materials be separated from the water again?
What is necessary to separate the solute (solid) and the solvent
(liquid) in each mixture?
What are the differences between the 2 materials?
Are both mixtures solutions? Explain.
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Materials

Filter apparatus
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Charcoal Powder
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Salt
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Scale
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Rock Candy
Investigate how heat changes the saturation point of water.
Observe sugar crystal formation
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Vocabulary
 Dissolve Soluble-
 Solution Precipitate Saturation-
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Investigation Questions
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Is sugar soluble in water?
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How does heating water change the amount of sugar that can
be dissolved in it?
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Why does heating a liquid increase its saturation point?
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Materials
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Clear cup or graduated cylinder.
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Sugar
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5cc measuring spoon.
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Electric teapot
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Stirrer
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Thermometer
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String
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Pencil
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Paper Clip
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Investigation
Part One: Saturation in Room Temperature H2O

Measure 1/2 cup of water (see milliliter conversion on the
next slide.)

Measure sugar into the water 5cc’s at a time.
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Stir for 20 seconds. Observe to see if the sugar has
precipitated.
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Repeat until a precipitate is observed.
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Milliliter/Cup Conversion
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Observations

How much sugar were you able to dissolve before the water
was saturated?
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How were you able to tell that the water was saturated?
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Part 2: Saturation in 100 Celsius
Water

Prepare the string, pencil, and paperclip
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Bring water to a boil.

Pour 1 cup of water into a graduated cylinder or jar.
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Mix in sugar 5cc’s at a time, stirring to dissolve. Stop when
the solution reaches its saturation point.
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Place the string in the jar.
Procedure at http://www.wikihow.com/Make-Rock-Candy
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Observations
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How did heating water change its saturation point?
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In which condition were you able to dissolve more sugar?
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Graphing sugar saturation with
temperature
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Why heating changes saturation
point…..
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Observe the molecular energy of water as its temperature is
increased.
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http://phet.colorado.edu/en/simulation/states-of-matterbasics
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Crystal Garden
Observe how solutions that contain salt form crystals when
evaporated.
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Objectives:

Follow a procedure, making accurate measurements.
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Describe how salts dissolve in solutions and leave
precipitates when a solvent is evaporated.
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Define and contrast solutes and solvents.
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Materials
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Distilled water.
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Laundry bluing.
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Sponge
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Table Salt (Sodium Chloride, NaCl)
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Food Coloring
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Plastic Container
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Graduated Cylinder
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Newspaper
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Ammonia
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5cc/mL measuring cup
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Container of water
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Procedure, Observation,
Conclusions
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A detailed, 2-day procedure is provided at
https://www.youtube.com/watch?v=SRtxWYSL0Pw
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Notes:
Lab Observation and Conclusion Reports
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Extensions
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Crystals forming during volcanic activity
http://www.classzone.com/books/earth_science/terc/conten
t/investigations/es0603/es0603page05.cfm
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Brainpop: Crystals
https://www.brainpop.com/science/earthsystem/crystals/
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Make rock candy http://www.wikihow.com/Make-RockCandy