Lab 4 - Acid Base Extraction Post Lab Report PDF

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Name: Ashley Blackwelder

Unknown Number(s): 2

Experiment Title: Acid-Base Extraction Section Day/Time: Monday PM

If Make-Up, lab performed on:_______________

Teaching Assistant: Jeffery Cullen Lab Technique: Leave this section blank in your report. But, make sure to tell Gradescope it is on page one of your lab report. Your TA will assign the technique points when they grade the post-lab. Do not delete this text. Purpose: To separate a mixture of an acid, base and and a neutral compound into its individual components. To Purify unknown 2 by re-crystallization and identify the compound by melting point determination. Pre-Lab: Leave this section blank in your post-lab report. But, make sure to tell Gradescope it is on the appropriate page. Your TA should have graded the prelab before you began the experiment. They will assign the awarded points for the prelab with the report. Do not delete this text. In-Lab Entries and Observations: • •

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The original amount of unknown was .250g, which is about .125g of each compound The Erlenmeyer flask that was being used in step 4 to collect the solid broke, and tertbutyl methyl ether was added to the broken flask to redissolve the liquid, was poured into a 250 mL beaker and was then evaporated once again. The beaker was 28791 mg without the product and 28793 mg with the product Some of the product was in the end because of this The compound in AE1 had a MP of 142-145o C which was able to be identified as 2chlorobenzoic acid The mass of the filter paper used for AE 1was 0.177 g. The actual product at the end was 0.045g. The percent recovery for AE 1 was 0.045/0.125 = .36 or 36% recovery The crystals for AE 1 was pink and needles, similar to cotton candy OL1 had a MP of 133-136o C which made it be able to be identified as benzoin The mass of the filter paper used for OL1 was 0.176g and the mass of the product at the end was 0.061g The precent recovery for AE1 is 0.061/0.125=.49 or 49% recovery The crystals for OL1 was powdery and white

Results:

Unknown 2 Final Mass

% recovery

Identity

AE1 OL1

36% 49%

2-chlorobenzoic acid benzoin

.045g .061g

Crystal Type Needle Powder

MP 142-145o C 133-136o C

Discussion: The purpose of this lab was to identify the components of unknown 2 through acid base extraction to separate the components, recrystallization to purify the compound, and finding the MP of the dried crystals. The final mass of AE1, identified as 2-chlorobenzoic acid, was 0.045g, and the percent recovery was 36%. The final mass of OL1 was 0.061g and the percent recovery was 49%. Part of the product was lost due to glass breaking, so percent recovery could be increased one by being more cautious. Precision from separating the compound with a pipet could have also bettered the outcome of this procedure. Cleanliness of glassware could be increased to decrease any potential contamination that occurred during the lab that fluctuated the MP of the substances.

Postlab Questions: 1.) In this experiment, if the carboxylic acid is benzoic acid, how many moles of benzoic acid are present (assume an equal portion of each component)? How many moles of sodium bicarbonate are contained in 1 mL of a saturated aqueous sodium bicarbonate? Is the amount of sodium bicarbonate sufficient to react with all of the benzoic acid? 1 mole of sodium bicarbonate reacts with 1 mol of benzoic acid. Solubility of NaHCO3 = 69 g / Liter = 0.069 g / ml Moles of NaHCO3 = mass / molar mass = 0.069 / 84 = 8.21 * 10-4 mol This is not enough to react with all of the benzoic acid 2.) To isolate the benzoic acid from the bicarbonate solution, the bicarbonate solution is acidified with concentrated HCl. What volume of acid is required to neutralize the bicarbonate? 3.) The ether solution is extracted with saturated aqueous sodium chloride. What is the purpose of this? Saturated sodium chloride \pulls water from the organic layer to dry it, and helps force the organic compound into the organic layer.. 4.) A mixture of benzoic acid and a neutral nonpolar compound is dissolved in ether and mixed thoroughly with aqueous sodium bicarbonate. What is the organic chemical species that is present in the ether layer? In the aqueous layer?

The AQ layer is benzoic acid, the ether layer is something non polar

5.)...