How Does Temperature Affect Crystal Growth?
What Are Crystals?
Crystals are structures that are formed from a regular repeated pattern of connected atoms
or molecules. All minerals are crystalline. Crystals grow by a process termed nucleation.
During nucleation, the atoms or molecules that will crystallize (solute) are dissolved into
their individual units in a solvent. The solute particles contact each other and connect with
each other. This is larger than an individual particle, so more particles will contact and
connect with it. Eventually, this crystal nucleus becomes large enough that it falls out of
solution (crystallizes). Other solute molecules will continue to attach to the surface of the
crystal, causing it to grow until a balance or equilibrium is reached between the solute
molecules in the crystal and those that remain in the solution.
Purpose
The purpose of this experiment is to determine which temperature (hot, cold or room
temperature) affects crystal growth rate the most.
Experiment:
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 provided 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.
Materials (per group):
2 250 mL beakers
Hot water bath, ice bath, room temperature (test tube stands)
Tape and marker
Epsom Salt (magnesium sulfate)
Copper Sulfate* (Copper Sulfate is an irritant, DO NOT INHALE and WASH SKIN
IMMEDIATELY AFTER CONTACT)
6 test tubes
Hot water (burn risk)
Mixing Spoon
1 test tube rack
DO NOT POUR COPPER SULFATE DOWN THE DRAIN
Procedure:
1. Acquire six test tubes and a test tube rack. Label six test tubes with a piece of tape
and your group names. Place test tubes in the rack.
2. Pour enough hot water from the boiler pot into two beakers to fill three test tubes.
3. In the first beaker add Copper Sulfate until the solution is saturated.
4. Allow to cool briefly (to touch) and then pour into 3 test tubes held in the test tube
rack. Be careful not to spill any solution or get any on your skin. If you do wash
immediately.
5. Pour any extra copper sulfate into “waste” beaker.
6. Add one seed crystal into each test tube.
7. Place one test tube in each of the three temperature stations.
8. Repeat steps 1-5 for the Magnesium Sulfate (Epsom salt)
9. Clean up your area, return all supplies, return to your seats.
Lab Write-Up:
In your notebook
1. identify the problem being addressed in this lab
2. identify the variables in this experiment
3. identify the controls in this experiment
4. write an introduction/discussion paragraph relating this lab to the study of minerals.
5. write a clear hypothesis predicting the results of this experiment.