ExtractionBy: Matthew P. Garcia*, Sahar Safaie, and Devin Miles

CHEM 2423: Dr. Houston Brown 16 August 2011

IntroductionThe purpose of the lab is to use extraction to separate of mixture of Benzoic acid and Naphthalene. Our hypothesis is through recrystallization we will then determine the two isolated compounds melting points and determine whether we have extracted the pure organic compounds successfully.

Materials: 0.27g of Naphthalene (dried Benzoic acid) Tert butyl methyl ether (MTBE) 2 small test tubes Sand bath Sodium Bicarbonate Pasteur pipette Test tube rack Funnel Filter paper Hydrochloric acid Drying pellets (anhydrous chloride) Meltemp 2 capillary tubes

Procedure

Separation of Naphthalene from Benzoic Acid

In a labeled small test tube, we transferred 0.2755g of Naphthalene/Benzoic acid mixture in the form of a dried powder; the mixture was pre-weighed using an analytical balance to record the exact weight. We then added 3ml of MTBE into the test tube along with 1.5ml sodium bicarbonate and will react with benzoic acid to produce a polar benzoic acid salt to react with water. Using a Pasteur pipette we rapidly flushed the mixture for ~3 minutes, pulling the two layers into the tube and forcefully expelling the solution into the reaction tube. After allowing the layers to separate using a pipette, removing the bottom layer, we carefully separated the benzoic acid from naphthalene into test tube #2. We then added another 0.25mL of sodium bicarbonate solution into test to #1, repeating the same procedure to remove any benzoic acid salt still present in solution. We then added 0.3ml of MTBE into test tube #2 to remove any organic material that may influence our data.

Isolation of Benzoic Acid

Under the hood, In test tube #2 we add HCl to convert the benzoic acid salt back into insoluble benzoic acid in small drops until the liquid stopped reacting (fizzing). We then heat the solution with a warm sand bath to bring the benzoic acid into solution. We filtered the remaining solution washing out the tube with a small quantity of ice water and allowed the crystals to dry to determine the mass of our product. Using a Meltemp we then measured our crystals melting point to validate pure samples are present.

Isolation of Naphthalene

To remove any water from test tube #1 we added anhydrous calcium chloride pellets to the tube until they no longer clump. We then separated the MTBE into a tarred test tube washing the pellets a couple of times to insure a complete transfer. We then left the test tube under the hood to dry for a week and measured the contents melting point for purity.

Data Melting Point

Starting (C°) Final (C°)

Benzoic Acid 80° 120°Naphthalene 82° 122°

Mass of CrystalsFilter Paper 1.5584g

Filter paper (+) benzoic acid 1.8088gIsolated Benzoic acid 0.2504g

Test tube 5.2151gTest tube +Naphthalene 5.2887gIsolated Naphthalene 0.0736g

Results We can safely assume we have isolated both pure benzoic acid and pure naphthalene as indicated by the corresponding known melting points.

We calculated the %yield for each compound

%yeild=( (actual yield )theoretical Yield ) x100

%yeild=( 0.07360.2755 )x 100=26.7 % Naphthalene

%yeild=( 0.2504 g0.2755 g )x 100=90.9%Benzoic acid

Problems

Benzoic acid (121.5-122°C

Naphthalene80-82°C

In test tube #2 we added the HCl to fast making the benzoic acid impossible to dissolve into solution, while mixing the solution with a glass-stirring rod our test tube broke. We preformed the experiment over again adding the HCl to the solution much slower.

DiscussionsBased on the percentage yield calculation of benzoic acid only 8.9% less then expected yield, which is pretty good seeing as we were experiencing many problems with the solution and was forced to start over. The experiment called for a Hirsh funnel, however we did not have one, this could be the cause for the low yield of Naphthalene. We allowed the samples to dry overnight in a closed hood, however with no one to supervise the hood, there could be a number of possibilities that could of affected our results, including air or dust coming into contact and contaminating our filtrate. We were able to separate the two layers in our mixture with the help of the substitution reaction of sodium bicarbonate to produce water soluble (polar) benzoic acid salt providing an effective reaction pathway for the extraction of the two compounds.

ConclusionBased on our experimentally determined melting points, we can conclude that we have successfully extracted pure benzoic acid and Naphthalene by methods of extraction and recrystallization, applying our knowledge of the organic compounds solubility properties.