Lab #2: Recrystallization


Recrystallization is a process that determines the purity of a compound or solid substance. The purpose of this lab was to think critically in testing solubility's of solids in different solutions with the goal of removing colored impurities through various filtration processes I need more here. More specific information, and just more of it.

One can refer to- for more detailed procedures- Experiments 1,2,4,7
Williamson K.L., 2003. Macroscale and Microscale Organic Experiments 4th Edition. Boston (MA): Houghton Mifflin Company, p. 38-64

Experiment #1:

In part one of the lab the solubility of several different compounds was (were) examined. Given the solids: Resorcinol, Anthracene and Benzoic Acid to test their solubility in: water, Toluene, and Ligrion. First the solids were tested in the different solvents at room temperature and then again with heat added. The results can be seen in figure 1.0.

Procedure: solubility testing

-To test the solubility of a solid, transfer about 10 mg into a reaction tube.
For this lab the solids are: Resorcinol, Anthracene or Benzoic Acid
- Add about 0.25 mL of solvent into the reaction tube using a pipette.
For this lab the solvents are: Water, Toulene, and Ligroin
- Observe possible reaction between two substances
- Record observations at room temperature when solvent is added.
- If the solid does not dissolve at room temperature, heat the mixture until it begins to dissolve.
If the mixture completely dissolves, it is said to be readily soluble in a hot solvent.
If some but not all of the mixture dissolves, it is said to be moderately soluble in a hot solvent.
- Take the solvent off of the heat and allow to cool so that the crystals can form.
- Repeat steps 1-6 so that all the solids are tested with each solvent.

Benzoic Acid
Soluble at room temp.
soluble when heated
soluble when heated
soluble when heated
Fig. 1.0
OK here: the table is good.

The solvents are on the y-axis on the left side and the solids are on the x-axis on the top.
I am accustomed to seeing "y-axis" and "x-axis" used for graphs. You confused me here, using it for a table.

-Resocinol dissolved in water at room temp but non of the other solvents at any heat. (none)
-Benzoin acid dissolved in toulene at heat but in no other solvent. (benzoic acid)
-Anthracene dissolved in toulene at heat but in no other solvent.
-The trends of these substances ability to dissolve in the solvents can be attributed to polarity; the basic rule for solubility and polarity is"like dissolves like" so a polar liquid like water cannot dissolve a very non-polar substance like anthracene.
-With a little online research the polarities of all the substances have been recorded in fig. 1.1.


Very polar
Very weak polarity
Benzoic Acid
Very weak polarity
Fig. 1.1

Experiment 2: Crystallization of pure pthallic acid

The provided solubility values for phthalic acid in water at 14°C (0.54 g solute per 100 mL solvent) and at 99°C (18 g solute per 100 mL solvent), the amount of solvent needed dissolve 60 mg of phthalic acid at 99°C this is unclear to me. What are you saying?
Solublility at 99°C: 18 g solute per 100 mL solvent
0.060 g phthalic acid * 100 ml H2O / 18 g phthalic acid = 0.33 ml H2O

-60 mg of phthalic acid was added to a micro-scale reaction tube, then 33 ml of water was added. 33 ml? The reaction tube was place in a hot sand bath. After the solute fully dissolved, it was left to cool to roughly to room temperature. Once cooled the reaction tube was place in a ice bath to further facilitate crystallization of the solute. After crystallization occurred, the left over water in the reaction tube was removed with a Pasteur pipette. Once all water was expelled, ethanol was added to remove water from the crystals. Finally, after the remaining liquid in the reaction tube was removed with a Pasteur pipette, the product was left to fully dry and then scraped onto a piece of filter paper with a spatula. The end result of the crystals was then weighted and final percent recovery calculated.
this appears to be incomplete.

Recovered Crystal weight:

Melting Point of Crystals:

Experiment 4: 15 grams of provided raw sugar was decolorized with Norit decolorizing charcoal pellets.

15 grams of raw sugar was dissolved in 30 mL of water in a 50 mL Erlenmeyer flask by placing the Erlenmeyer flask in a hot sand bath. Once the raw sugar had fully dissolved in the water, half of the solution was poured into another 50 mL flask. Then, one of the solutions was heated to near its boiling point, allowed to cool slightly, and 250 mg of decolorizing charcoal was added. Once added the solution was then place into the sand bath and brought to a boil for two minutes. Once boiled for two minutes, the hot solution was then filtered into an Erlenmeyer flask through a heated vacuum filtration. Then with the other half of the solution, repeat the process but only use 50 mg of decoloizing charcoal.


-Stirring help promoted the raw sugar to dissolve faster.
-There were no observable differences between the solution with 250 mg of decolorizing charcoal and the solution with 50 mg. After both were filtered, both were a amber yellow.
-Neither of the solutions crystallized. This could have been because the lab procedure called for the use of brown sugar not raw sugar.
Remember I mentioned that we have tried brown sugar in the past? That's why we were working with raw sugar. OK on the analysis in this section.

Experiment 7:

First a 90%/10% ethanol/water mixture was made. Then, roughly 180 mg of the provided solute was dissolved in the ethanol/water mixture. The mixture was to be heated in a sand bath. Once the mixture had fully been saturated with the solute, the undissolved/suspended solids were filtered through a vaccum filter apparatus. The resulting solution was allowed to cool to room temperature. Once cooled the solution was placed into an ice bath to help promote crystallization. After crystallization occured one was to expel any remaining liquid by using a Pasture Pipette. The resulting crystals were weighed and percent recovery calculated. The melting temperature of the resultant crystals was also measured.

Resulting Crystal weight:

Melting Point of substance:
again, this appears incomplete.

Post Lab Question:

Ty Trate has been feverishly working in the Organic lab to recrystallize a substance he synthesized using the Nobel-award-winning Heck reaction. Ty started out with 1.106 grams of product with a m.p. of 131.6-144.3°C. After recrystallizing from an ethanol/water mix, he is left with 0.884 g of product that melts from 143.7-144.9°C.

1. Calculate the percent recovery for Ty (he has trouble with math), reporting your answer with an appropriate number of significant figures. Show your work.

-0.884 g / 1.106 g * 100 = 79.9% Recovered

2. Then tell me whether Ty appears to have succeeded in purifying his product during the recrystallization, and explain to me how you know.

-The results that Ty Trate received reflects that he succeeded in purifying his product. A way in determining this was by comparing the first melting point 131.6-144.3°C and then the new melting point 143.7-144.9°C. The new melting point scale (range) is tighter then the first one which shows that there was less impurities in the new sample