+

Crystals

Conduct observations of the physical properties of crystals. Dissolve and recrystallize materials.

+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.

+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?

+Key Vocabulary

Mass-

Volume-

Density-

Physical Property-

Dissolve-

Crystallize-

Solubility-

+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 1Describe the Characteristics of 4 Crystals

+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

+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.

+Observation:Characteristics of Each Crystal

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Part 2: CrushabilityAfter observing physical characteristics of each crystal, crush the crystals and compare their “crushability.”

+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.

+Investigation Question

Can you use a “crushability” test to compare the unknown crystal to the other crystals?

+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

+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.

+Observations and Conclusions

Complete student worksheet 2.2

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Part 3: DissolvingUse the solubility of each crystal to compare the crystals to an unknown.

+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.

+Which material do you think would have greater solubility?

+Investigation Question

Can you compare the unknown material to the other materials by comparing their solubility?

+MaterialsTable Salt

Epsom Salt

Road Salt

Sugar

Unknown Crystal

5 Clear Plastic Cups

5 Paper Cups

Spoon

Warm Water

Scales

Marker or Pen

+Procedure

Label each cup with the crystal that will be dissolved into it.

Weigh 5g of each crushed crystal in a paper cup.

Measure 1teaspoon of warm tap water into each cup.

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.

Pour the solution back into it’s paper cup. Be careful not to pour out undissolved crystals.

Compare the amount of undissolved crystals in each cup.

Repeat 2 more times.

+Observations and Conclusions

Record observations using 2.3 Solubility Test

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Part 4: CrystallizationObserve the recrystallization of each solute. Compare the appearance of the unknown material with each material .

+Scientific Background

Because of it’s characteristic properties, every solid crystallizes in a unique way.

Crystals are generally formed when the solvent (liquid) evaporates leaving the solute (solid.)

+How did these crystals form?

+Investigation Question

Can you identify the unknown crystal by comparing its appearance to the other materials when it crystallizes?

+Materials

Magnifying Glass

Wells containing samples of each solution from part 3.

+Procedure

Observe each crystallized solute to compare their characteristics.

+Observation and Conclusion

Complete 2.4 Recrystallization Test

Read and complete the Review and Apply Worksheet

Read and complete Think About It

+

Mixtures and SolutionsMixtures and solutions are both combinations of 2 or more substances.Mixtures can be separated with a filter, solutions can only be separated using evaporation.

+Vocabulary

Solution-

Mixture-

Suspension-

Dissolve-

Filter-

Evaporate-

+Key QuestionsWhen 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.

+Materials

Filter apparatus

Charcoal Powder

Salt

Scale

+

Rock CandyInvestigate how heat changes the saturation point of water. Observe sugar crystal formation

+Vocabulary

Dissolve-

Soluble-

Solution-

Precipitate-

Saturation-

+Investigation Questions

Is sugar soluble in water?

How does heating water change the amount of sugar that can be dissolved in it?

Why does heating a liquid increase its saturation point?

+Materials

Clear cup or graduated cylinder.

Sugar

5cc measuring spoon.

Electric teapot

Stirrer

Thermometer

String

Pencil

Paper Clip

+InvestigationPart 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.

Stir for 20 seconds. Observe to see if the sugar has precipitated.

Repeat until a precipitate is observed.

+Milliliter/Cup Conversion

+Observations

How much sugar were you able to dissolve before the water was saturated?

How were you able to tell that the water was saturated?

+Part 2: Saturation in 100 Celsius Water

Prepare the string, pencil, and paperclip

Bring water to a boil.

Pour 1 cup of water into a graduated cylinder or jar.

Mix in sugar 5cc’s at a time, stirring to dissolve. Stop when the solution reaches its saturation point.

Place the string in the jar.

Procedure at http://www.wikihow.com/Make-Rock-Candy

+Observations

How did heating water change its saturation point?

In which condition were you able to dissolve more sugar?

+Graphing sugar saturation with temperature

+Why heating changes saturation point…..

Observe the molecular energy of water as its temperature is increased.

http://phet.colorado.edu/en/simulation/states-of-matter-basics

+

Crystal GardenObserve how solutions that contain salt form crystals when evaporated.

+Objectives:

Follow a procedure, making accurate measurements.

Describe how salts dissolve in solutions and leave precipitates when a solvent is evaporated.

Define and contrast solutes and solvents.

+Materials

Distilled water.

Laundry bluing.

Sponge

Table Salt (Sodium Chloride, NaCl)

Food Coloring

Plastic Container

Graduated Cylinder

Newspaper

Ammonia

5cc/mL measuring cup

Container of water

+Procedure, Observation, Conclusions

A detailed, 2-day procedure is provided at https://www.youtube.com/watch?v=SRtxWYSL0Pw

Notes:

Lab Observation and Conclusion Reports

+Extensions

Crystals forming during volcanic activity http://www.classzone.com/books/earth_science/terc/content/investigations/es0603/es0603page05.cfm

Brainpop: Crystals https://www.brainpop.com/science/earthsystem/crystals/

Make rock candy http://www.wikihow.com/Make-Rock-Candy