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.

Part 1 Describe 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

Part 2: Crushability After 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

Part 3: Dissolving Use 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?

Materials Table 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

Part 4: Crystallization Observe 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 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.

Vocabulary Solution- Mixture- Suspension- Dissolve- Filter- Evaporate-

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.

Materials Filter apparatus Charcoal Powder Salt Scale

Rock Candy Investigate 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

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. 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 Garden Observe 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/conten t/investigations/es0603/es0603page05.cfm Brainpop: Crystals https://www.brainpop.com/science/earthsystem/crystals/ Make rock candy http://www.wikihow.com/Make-Rock- Candy