Use of Extraction to Isolate a Neutral Compound from a Mixture Containing an Acid Impurity.
Introduction: The purpose of this lab was to separate and purify a compound. This was achieved using techniques that allowed the extraction of the acid, the isolation of the neutral compound and the melting point classification of the neutral compound to test the purity of the sample. Chemical Reactions: HA+OH-? A-+H2O R-COOH+OH-? R-COO-+H2O Organic Acid Insoluble in H2OConjugate base Soluble in H2O Procedure: A 0. 170g sample consisting of a mixture of 0. 110g of an unknown neutral compound and 0. 060g of benzoic acid was mixed with ether and shaken until all solids dissolved.
NaOH was added, shaken, allowed to separate and the bottom layer removed and transferred to a test tube labeled “NaOH 1st extract”. NaOH was again added to the remaining original mixture, shaken, allowed to separate and the bottom aqueous layer was removed and transferred to a test tube labeled “NaOH 2nd extract”. HCl drops were added to both NaOH extracts until the mixtures turned acidic and a precipitate formed. NaCl was added to the original mixture, shaken and allowed to separate. The aqueous layer is removed and discarded. The remaining ether layer is transferred to a clean test tube and dried over granular anhydrous sodium sulfate.
The dried ether solution is heated ina water bath until any remaining ether evaporated and only the unknown ingredient is left. The purity of the sample was verified by melting some of the crystallized sample and comparing the observed melting point range to the given melting point range of the listed unknown in the lab manual. Calculations: % Yield Recovery of sample= (end mass/starting mass) x 100 (0. 050g / 0. 170g) x 100 = 29. 41% ? Results: Starting sample mass:0. 170g Unknown Mixture composed of: Neutral compound: 0. 110g Benzoic acid: 0. 060g Test tube mass:19. 03g Test tube and sample mass:19. 8g Final sample mass:00. 05g Percent yield recovery: (0. 050g / 0. 170g) x 10029. 41% Melting Point of sample:82. 0-83. 0° C Melting Point – Book Reference:82. 0-85. 0° C – Fluorenone 116. 0-117. 0° C – Fluorene 139. 0-142. 0° C – 1,2,4,5-tetrachlorobenzene Observations:1st NaOH extract: white, cloudy precipitate formed. Test paper turned pink after 6 drops of HCl were added. 2nd NaOH extract: clear mixture. Test paper turned pink after 10 drops of HCl. Unknown neutral compound: crystallized yellow substance. Table 2 – Sample Information Team #6 results for our experiment. Discussion:
In this experiment, acid was extracted from a mixture and a neutral unknown compound was isolated and identified. This experiment relied on the reaction of the organic acid that was insoluble in water with a base that caused the loss of a proton and yielded a negatively charged conjugate base that became soluble in water. This interaction caused a separation of the mixture into an ether layer and a denser aqueous layer. The aqueous layer was extracted and transferred into two test tubes where HCl was added. HCl acted as a proton donor to the acid in the aqueous layer and caused the acid o precipitate out of solution. This was the reason for the white, cloudy precipitate substance that was observed in the test tube. The Litmus paper test further confirmed that these mixtures only contained acid because of the pink color reading. If anything other than acid would have remained, the color of the paper would have been blue or purple not pink. The ether layer still contained the neutral unknown compound that we wanted to isolate to be able to identify. Granular anhydrous sodium sulfate was used to dry the ether solution which was separated and the sodium sulfate was discarded.
A hot water bath was used on the separated ether layer to evaporate the ether. The remaining crystallized solid is the final purification of the sample. Only substances in their pure state will crystallize. The purity of the crystallized sample was further tested by taking the dried sample’s melting point. The melting point of our sample was 82. 0-83. 0° C is right within the expected temperature range listed in our lab manual for Fluorenone which has a melting point of 82. 0-85. 0° C. The percent yield re recovery was 29. 41%.
Some loss is always expected in all experiments but almost 70% loss is very high. This difference can be attributed to the sample that adhered to the test tube sides and the pipette shaft when the sample’s layers were being separated and transferred per the lab’s instructions. Also, when the ether layer needed to be completely segregated from the aqueous layer that was discarded some of the ether mixture was also discarded. Infrared Spectroscopy was done for the unknown and Benzoic Acid. Infrared Spectroscopy is used to identify molecules by giving structural information about a molecule.
Based on the knowledge that CH bonds have an absorption rate of 3000+-100cm-1 and that C=O bonds (carbonyl groups) have a 1700+- 100cm-1 absorption rate. I was able to locate these types of bonds on the Infrared Spectroscopy reports done by Dr. Yamaguchi. I don’t have enough expertise on how to decipher the other peaks and valleys in the report and cannot make any firm conclusions in regards to the Infrared Spectroscopy reports. Conclusion: This was a successful experiment in that we were able to extract the acid from the neutral compound and were able to purify and identify the unknown substance in our mixture.
Our team was able to purify Flourenone and test the purity of the sample successfully. I would like to learn a little more about the Infrared Spectroscopy reports to be better able to put this information to use. 1. Answer the following questions about the first and second NaOH extracts. a. Comment on the amount of precipitate for both extracts when HCl is added. The amount of precipitate varied between the first and the second NaOH extracts. The first extract had more precipitate than the second extract. b. What is the precipitate formed when HCl is added? Benzoic Acid. c.
Does the amount of precipitate in each tube indicate that all the acid impurity has been removed from the ether layer containing the unknown neutral compound? Yes. The second extract has a considerably less amount of precipitate than the first extract leading me to believe that when the HCl was added to the second extract mixture and acted as a proton donor to the acid in the aqueous layer there wasn’t much acid to precipitate out of solution. 2. Report the melting point and weight of the neutral compound you isolated. 82. 0-83. 0° C; 3. Based on the melting point, what is the identity of this compound? 2. 0-85. 0° C – Fluorenone 4. Calculate the percent recovery for the neutral compound. List possible sources of loss. The percent yield re recovery was 29. 41%. Some loss is always expected in all experiments but almost 70% loss is very high. This difference can be attributed to the sample that adhered to the test tube sides and the pipette shaft when the sample’s layers were being separated and transferred per the lab’s instructions. Also, when the ether layer needed to be completely segregated from the aqueous layer that was discarded some of the ether mixture was also discarded.