Growing Crystals

Author(s): Nabila Jahchan and Gertie

Growth & Development Experiment 
SED 695B; Fall 2005

\Research Question:

Do all salt crystals look the same? LetŐs grow crystals from different salt solutions and find out.

 


 

 

Standards addressed:

2. Biological, chemical, and physical properties of matter result from the ability of atoms to form bonds from electrostatic forces between electrons and protons and between atoms and molecules. As a basis for understanding this concept:

Students know salt crystals, such as NaCl, are repeating patterns of positive and negative ions held together by electrostatic attraction.

 

Independent variable

Dependent variables

Controls

Series

 Time

Crystals shape of different salts

Same environment

Same solvent

Same ambient temperature

 Alum

 Copper sulfate

 Sodium acetate

 Sodium chloride

 Potassium ferricyanid

 

 

 

 

 

Materials

Procedures

 *         Soluble salts

*          warm water

*          clear glass or plastic container

*          coffee filter or paper towel

*          string/pencil (optional)

*          spoon or stirring rod

 

*          Make a saturated solution.

*          Start a garden or grow a seed crystal.

*          Continue growth.

 

In order to grow a crystal, you need to make a solution which maximizes the chances for the solute particles to come together and form a nucleus, which will grow into your crystal. This means you will want a concentrated solution with as much solute as you can dissolve (saturated solution). Sometimes nucleation can occur simply through the interactions between the solute particles in the solution (called unassisted nucleation), but sometimes it's better to provide a sort of meeting place for solute particles to aggregate (assisted nucleation). A rough surface tends to be more attractive for nucleation than a smooth surface. As an example, a crystal is more likely to start forming on a rough piece of string than on the smooth side of a glass.

 

Make a Saturated Solution

 

It's best to start your crystals with a saturated solution. A more dilute solution will become saturated as the air evaporates some liquid, but evaporation takes time (days, weeks). You will get your crystals more quickly if the solution is saturated to begin with. Also, there may come a time when you need to add more liquid to your crystal solution. If your solution is anything but saturated, then it will undo your work and actually dissolve your crystals! Make a saturated solution by adding your crystal solute (e.g., alum, sugar, salt) to the solvent (usually water, although some recipes may call for other solvents). Stirring the mix will help to dissolve the solute. Sometimes you may want to apply heat to help the solute dissolve. You can use boiling water or sometimes even heat the solution on the stove, over a burner, or in a microwave.

 

 

 

 


 

 


 

 

 


References & Links:

http://www.geocities.com/rainforest/canopy/2525/crystals/

http://chemistry.about.com/od/growingcrystals/

http://www.ed.gov/pubs/parents/Science/crystals.html

http://rockhoundingar.com/pebblepups/growcryst.html