Post Lab Experiment 4_Kamya Campbell

pdf

School

University of Massachusetts, Amherst *

*We aren’t endorsed by this school

Course

269

Subject

Chemistry

Date

Apr 3, 2024

Type

pdf

Pages

Uploaded by kamyacampbellu

Name: Kamya Campbell Unknown Number(s): 5 Report Submission Date: Click or tap to enter a date. Experiment Title: This is a dropdown list. Choose the name of this technique experiment: Section Day/Time: Friday AM If Make-Up , lab performed on:_______________ Teaching Assistant: Aniket Majee 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 identify the unknown carboxylic acid and unknown neutral compound of compound 5, a mixture of equal parts will be separated using acid-base extraction techniques. The unknowns' melting point ranges will be determined and compared to those of known compounds. Pre-Lab : Leave this section blank in your post-lab report. In-Lab Entries and Observations : • Unknown sample from #8 to #5 • Assuming 1:1 ratio of unknown, each compound weighs 250/2 = 125 mg AE1: (carboxylic acid) • Initial weight: • Weight of filter paper: 488 mg • Weight of crystals + filter paper: 495 mg • Weight of AE1 crystals: 7 mg • Percent Recovery (0.007/0.125)*100 = 5.6% • Melting Point: 123-130 C o Melting point was checked twice. o Started melting at 123 and ended fully between 129-130 OL1 (unknown neutral Compound) • Initial Weight: 125 mg • Weight of Erlenmeyer Flask (With Product): 23.865 g • Weight of filter paper: 450 mg • Weight of OL1 crystals + filter paper: 482 mg • Weight of Crystals: 32 mg • Percent Recovery: (0.032/0.125) *100 = 25.6 % • Melting Point: 124-126 C

o Melting point done twice o Droplets at 125 and ended fully melted at 126 Results (modify table as needed): Delete this and the parenthetical text Compound Final Mass (g) % Recovery MP(C ) Identity AE1 0.007 g 5.6 % 123-130 C Benzoic acid OL1 0.032 g 25.6% 124-126 C trans-stilbene Discussion : The The primary goal of this experiment is to separate the unknown sample #5, which contains approximately equal amounts of an unknown carboxylic acid and an unknown neutral compound. The unknown compounds will be determined using melting point detection methods. The isolated product, AE1, was extracted from the unknown sample and purified to determine the identity of the carboxylic acid. AE1's crystals had a final mass of 0.032 grams. When the crystal mass was compared to the expected mass of carboxylic acid in the 0.25 grams of unknown sample, the final percent recovery was 5.6%. The AE1 crystals' melting point was also determined to be between 123 and 130°C. The crystals' melting points revealed that the carboxylic acid was benzoic acid, which has a melting point of 122°C. Given the melting range of only 2 to 7 °C, the sample is assumed to be relatively impure. The entire solution must pass through the ether and sodium bicarbonate mixture for the results to be valid. This is to ensure that the compound is properly divided into two layers. Submerging the AE1 layer in the mixture multiple times results in a more accurate and higher percent recovery. This is not the only way to improve percent recovery; using the correct amount of HCl to precipitate the carboxylic acid is also important. If an adequate amount of HCl was not used in the experiment, there would be insufficient solid mass, resulting in a low percent recovery. The OL1 product was isolated from the unknown sample 4 and recrystallized to aid in the determination of the overall neutral compound. The OL1 crystal recovery produced a final mass of 0.032 grams. The percent recovery was 25.6% when compared to the neutral compound's initial mass of 0.251 grams. In terms of melting point, OL1 crystals melted at 124-126°C. When this was compared to the values of possible neutral compounds, it was discovered that the sample was trans-stilbene. It should be noted that the OL1 sample was relatively pure due to its narrow melting point range of 1°C. The percentage recovery increases with each wash of the sample, so it would have been higher if the OL1 solution had been washed for more than one minute. Finally, the crystals' percentage recovery could have been higher if they had passed through more ice-cold solvents. This allows a larger portion of the sample to be removed from the flask and transferred to the vacuum suction, resulting in crystals. 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 the benzoic acid? a. Assuming equal amounts, the compound would contain 0.001 moles of benzoic acid. The saturated sodium bicarbonate solution in 1 mL contains 0.001 moles. To achieve neutrality, a 1:1 ratio is necessary. 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? a. To neutralize 1mL of saturated sodium bicarbonate, you need 0.083 mL of HCl. 3) The ether solution is extracted with saturated aqueous sodium chloride. What is the purpose of this? a. To remove water from the ether solution, extract it with sodium chloride. This will continue to dry, leaving the OL1 product in the vile. 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? a. The ether layer contains neutral, non-polar organic compounds, while the aqueous layer contains sodium benzoate. 5) Construct a flow chart that follows the separation of a mixture of 2-nitrophenol (an organic acid not used in this experiment with a pKa = 7.26) and anthracene (neutral organic). Use scheme 1 as a template. Your reagents available are the same ones used in this lab. On the next page:

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version