Recrystallization (Page 3 of 4) in pdf

completely dissolves at elevated temperature, record that it is soluble in the hot solvent.

If some but not all dissolves, record that it is slightly soluble, and continue to add drops

of solvent until dissolution is complete. Once the substance has been dissolved in hot

solvent, allow the solution to cool to room temperature, then stick the test tube in ice. If

necessary, induce crystallization by rubbing the walls of the tube with a stirring rod.

Describe the nature of the crystals that form (for example, needles, plates or blocks). If

the solid remains undissolved even at elevated temperature, simply record it to be

insoluble in both the hot and cold solvent.

If the solid dissolves in methanol, ethanol, acetone or acetic acid at room

temperature, add a few drops of water to the solution to see if the solid precipitates. If it

does, heat the mixture in the water bath and observe if the solid re-dissolves. Adjust the

composition by adding drops of solvent and/or water as necessary until the solid has just

dissolved and the solution is saturated at the boiling point. Allow the solution to cool to

room temperature, then stick the test tube in ice. Describe the shape of the crystals which

form. Do not add water to either toluene or ligroin since it is not miscible with these

solvents.

Pour the mixtures contained in your test tubes into the Laboratory Byproducts

jar.

Notes:

• Acetic acid will freeze when placed in ice. Do not interpret frozen acetic acid

as crystal formation.

• Ligroin will evaporate quickly when placed in boiling water. Cool down your

water bath (by adding ice) before heating a test tube that contains ligroin.

Prepare a table in your notebook before coming to lab in which you will record

your observations. You will need to record the solubility at room temperature, the

solubility at elevated temperature, the result of adding water to a solution of the

compound (when applicable) and the appearance of the crystals.

In order to write a complete discussion for

Assignment

1, you will need to use the

Spartan software that can be found on the computers located in the lab. Bring the

Molecular Modeling

PDF document to lab with you, both for this experiment and for

Experiment 2. Find time during these two lab periods to build the molecules used in

Experiment 1, Part 2. Solubility Tests. Your TA will assist you, and you may work on it

with other students.

Recrystallization Page 3