Have you read the introductory section on Recrystallization?. If not, then do so now. It explains some terms and gives the backround behind this process. Then come right back here. The wizard will wait for you :-)

HERE's WHAT YOU NEED

• Substance to be crystallized
  
• A seed crystal of the substance to be crystallized on a fishing line
  
• Distilled or demineralized water
  
• A small wood rod or popsicle stick
  
• Thermometer
  
• Balance
  
• Plastic or glass container
  
• Heating plate
  
• Beaker of 2 to 4 litres
  

OPTIONAL

• Thermostated bath
  
• Slow revolution motor (1 to 4 rotations per day)
  

WHAT SUBSTANCES ARE RECOMMENDED?

Thus far, the Chemical Institute of Canada Crystal Growing Contest has used only three different substances:

1. Cupric sulfate pentahydrate (copper (II) sulfate pentahydrate) (or "bluestone");
   
2. Aluminum potassium sulfate (or "alum");
   this substance seems to be a popular one with which to experiment; see other procedures by Jeremy
   
3. Potassium sodium tartrate (or "Rochelle Salt").
   
   The choices were made on the basis of relative safety, availability, and good crystal growth. The first two are available from most laboratory chemical supply houses. The third may be made from materials found in a grocery store.
   

   Others that are known to give good crystals include:
   

4. Potassium ferricyanide,
   
5. Copper acetate monohydrate, and
   
6. Calcium copper acetate hexahydrate.
   

HERE's WHAT YOU NEED TO KNOW

1. How much substance you have to work with (weigh on a balance).
   

2. The solubility of the substance in water at room temperature. (Obtain from a chemistry reference book.)
   

3. It would also be useful to know the solubility of the substance at elevated temperatures.
   

HERE's WHAT YOU DO ...

... TO PREPARE A SUPERSATURATED SOLUTION

The amounts of substance and water to be used will depend upon the solubilities at room and elevated temperatures. You may have to determine the proper proportions by trial and error (just like the first scientists did).

METHOD ONE

1. Place about double the amount of substance that would normally dissolve in a certain volume of water at room temperature into that volume of water. (E.g., if 30 g [about 1 oz] of X dissolves in 100 g (mL) of water at room temperature, place 60 g of X in 100 mL of water.) Adjust the proportions depending upon how much material you have. Use clean glassware.
   

2. Stir the mixture until it appears that no more will go into solution.
   

3. Continue stirring the mixture while gently warming the solution.
   

4. Once all of the substance has gone into solution, remove the container from the heat.
   

5. Allow the solution to cool to room temperature.
   

You now have a supersaturated solution.

METHOD TWO

1. Select an appropriate volume of water.
   

2. Warm this water to about 15-20 deg above room temperature.
   

3. Add some of your substance to the warm water and stir the mixture all dissolves.
   

4. Continue adding substance and stirring until there is a little material that won't dissolve.
   

5. Warm the mixture a bit more until the remaining material goes into solution.
   

6. Once all of the substance has gone into solution, remove the container from the heat.
   

7. Allow the solution to cool to room temperature.
   

You now have a supersaturated solution.

FINALLY! HERE's WHAT YOU DO ...

... TO START GROWING YOUR WONDERFUL CRYSTAL

Since the solubility of a substance varies a lot with temperature, it is very important to control the temperature carefully.

If the room temperature is stable then you might be able to leave your apparatus out in the open. If it can vary by even only a degree or two, then it may be necessary to place the apparatus into a thermostated bath few degrees above room temperature (if available but not mandatory). You could also place the growing apparatus inside a styrofoam or picnic cooler.

Also, for the seed crystal to grow, it is absolutely necessary that the solution never be unsaturated at the temperature of the experiment (usually the room temperature).

OK, LET's START

1. Carefully suspend your seed crystal from the stick into the supersaturated solution, being careful not to let the crystal touch the bottom of the container.
   

2. Cover the container in which the crystal is growing. This is to:
   
   • keep out dust, and
     
   • reduce temperature fluctuations.
     
   This can be done with plastic wrap or aluminum foil. If you want to allow the solvent (typically water) to evaporate (see step #4a below), then use porous paper (e.g., filter paper).
   

3. Observe the crystal growth. Depending upon the substance, the degree of supersaturation, and the temperature, this may take several days before the growth slows down and stops.
   

   WHY DOES THE CRYSTAL STOP GROWING?
   

   A crystal will only grow when the surrounding solution is supersaturated with solute. When the solution is exactly saturated, no more material will be deposited on the crystal. (That may not be entirely true. Some may be deposted, however an equal amount will leave the crystal surface to go back into solution. We call this an equilibrium condition.)
   

   WHY DID MY CRYSTAL SHRINK/DISAPPEAR?
   

   If your crystal shrank or disappeared, it was because the surrounding solution became unsaturated and the crystal material went back into solution. Unsaturation may occur when the temperature of a saturated solution increases, even by only a few degrees, depending upon the solute. (This is why temperature control is so important.)

   HOW DO I GET CRYSTAL GROWTH RESTARTED?
   

4. Resupersaturate the solution. This may need to be done on a daily basis, especially when the crystal gets larger. But first, remove the crystal.
   
   • One way to resupersaturate the solution is to reduce the amount of solvent. This may be done by heating the solution for a while and then cool it to the original temperature. Or, you can just let the solvent evaporate from the solution (this may be a slow process, but has the advantage of getting a better quality crystal.)
     

   • One can also supersaturate the solution by warming it somewhat, then adding and dissolving more solute, and finally cooling it.
     

5. Each time the solution is saturated, it is a good idea to "clean" the monocrystal surface, by
   
   • making sure the crystal is dry,
     
   • not touching the crystal with your fingers (hold only by the suspending line if possible),
     
   • removing any "bumps" on the surface due to extra growth,
     
   • removing any small crystals from the line.
     
   It is a good habit to clean your hands after each manipulation.
   

6. Resuspend the crystal back into the newly supersaturated solution.
   

7. Repeat steps 4-6 as needed.
   

8. To get improved symmetry and size, slowly rotate the growing monocrystal (1 to 4 rotations per day). An electric motor with 1 to 4 daily rotations might be difficult to find (consider one from an old humidity drum-register or other apparatus). This "option" becomes useful only when a monocrystal gets rather big.
   

FOR PROFESSIONAL INSTRUCTIONS...
... on how to grow crystals, go to Paul Boyle"s article "Growing crystals that will make your crystallographer happy".

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