Lab Report 1 (Chem 2210) PDF

Preview

Summary

Download Lab Report 1 (Chem 2210) PDF

Description

Chem 2210

Laboratory Report 1: Form and Function Student Name: Polyvyana Anna Lab Section: B06

1. a) Figure 1. Screen shot of the Combined Chemical Dictionary (CCD) search results and the citation (below):

(1) Combined Chemical Dictionary (CCD); [Online]; http://ccd.chemnetbase.com.uml.idm.oclc.org/faces/chemical/ChemicalSearchResults.xhtml (accessed 6 October, 2017). b) Figure 2. Screen shot and citation (below) in ACS format of the primary literature source containing the melting point data:

(2) Zajac, M. A., Zakrzewski, A. G., Kowal, M. G., & Narayan, S. (2003). A novel method of

caffeine synthesis from uracil. Synthetic communications, 33(19), 3291-3297.

2. Percent recovery Percent recovery is used in cases where no chemical reaction is taking place, as in purification of the sample.

Percent yield Percent yield is used in cases where a chemical transformation occurs.

For Experiment 1, percent recovery must be used, because recrystallization did not involve any chemical reactions:

% recovery = amount of pure product recovered (g) /amount of crude material used(g) X 100

The calculations can not be done because I forgot to write the mass of the product recovered.

For Experiment 2, percent recovery must be used, because distillation did not involve any chemical reactions: % recovery = volume of pure product recovered (mL) / amount of crude material used (mL) X100 % recovery = 2.2 mL /20.0 mL = 11% 3.Calculation of Rf values My measurements: The distance the solvent traveled on the TLC plate = 36 mm Compounds

Distance traveled

Unknown

3 mm

Unknown + Suspected compound

2.8 mm

Suspected compound (caffeine)

3 mm

Rf = Distance the compound traveled / Distance the solvent traveled

Rf value of the unknown compound = 3 mm/36 mm = 0.08

Figure 3.TLC plate (Ethyl acetate)

Figure 4. TLC plate (Petroleum ether)

The Rf values calculated for the TLC plate with petroleum ether as an eluent are expected to be smaller than those with ethyl acetate. The suspected compound, caffeine, is an organic compound and is strongly attracted to the organic adsorbent on the plate (silica gel). This assumption is justified by the fact that if the compound was non-polar, it would not be attracted to the adsorbent that much and would move up the TLC plate more rapidly. Petroleum ether is a less polar solvent than ethyl acetate and is therefore less attracted to the polar unknown compound. So, the unknown compound will not dissolve as well in petroleum ether solvent and will move less distance up the TLC plate. And because Rf value is directly proportional to the distance the compound travels, the final result is expected to be a smaller value. 4.

For Experiment 1, Unknown A was used. The pure solid material obtained after the suction

filtration was dry, white and fluffy, forming big white chunks. From this data alone, no conclusions about the compound's identity can be made. Melting point for the unknown compound was determined to be in the range 235-238 Cº, with the noticeable phase transition at 190 Cº. This melting point value it very similar to the one of caffeine found in the literature (237.8)(3). So, I used caffeine as my suspected unknown compound further in the experiment. Also, the mixture of an unknown compound with caffeine produced the melting poing of 238 Cº. The experimental melting points are very similar, within the range of +-1.5 Cº and this is a strong evidence that the unknown compound and the suspected unknown compound are identical. In the TLC analysis, several pieces of information were tested. Apart from purity, discussed in section 5, TLC also helped to test identity of the compound. As the Rf values of all 3 compounds

analyzed were the same (0.08), those compounds are most probably identical. Another observations to support the hypothesis that the unknown compound is organic were that the compounds traveled little distance on the TLC plate, which can be expained by the attraction to the organic adsorbent on the plate (silica gel).

Table 1. Melting point Compound

Experimental Melting

Literature Melting

Point (Cº)

Point (Cº)

Unknown

235-238

Mixed Sample

238

Reference

(Unknown+Suspected compound (caffeine)) Caffeine

237.8

3

Table 2. TLC Compound

Rf

Conditions

Unknown compound

0.08

Eluent: Ethyl Acetate

Unknown + Suspected

0.08

Plate: Silica gel Visualization method: UV

compound Suspected compound (caffeine) 0.08

For Experiment 2, Unknown 1 was used. The majority of the distilled liquid was collected when the boiling point remained constant at 54 Cº. The range of temperature when the liquid was collected corresponded to the range of +-5 Cº stated in the Experiment Procedure Section of the Lab Manual (4).The value is very close to the literature boiling point of acetone (56 Cº)(5). So, acetone is my suspected unknown. In the second part of the experiment, gas chromatography was done for acetone, isopropanol and the distilled unknown. From the GC plot, it is noticeable that the character of the unknown sample graph is very similar to the acetone graph. Moreover, the retention time measured for the unknown sample (1 min) is very close to the acetone value (1.04 min). This is a strong proof that two compounds are identical.

Table 3. Boiling point Compound Acetone

Experimental Boiling

Literature Boiling Point Reference

Point (Cº)

(Cº) 56

5

Isopropanol Unknown

82

6

54

Table 4. GC Compound

Retention time (min)

Conditions

Acetone

1.04

Start temperature: 30 Cº

Isopropanol

1.42

Hold time: 0 min

Distilled Unknown Sample

1

Ramp Rate: 5 Cº/min Final Temperature: 30 Cº Hold time: 4 min Total length:4 min Pressure: 7 kPa

5.

In experement 1, the purity of my final isolated unknown can be analyzed based on the

melting point determination. The value range recorded in the lab (235-238 Cº) is including the value for caffeine found in the literature (237.8 Cº) (3). Mixture sample of the unknown compound and caffeine melted at 238 Cº. The range of melting points recorded is very narrow, and the test for the melting point of the mixture of both compounds proved they are identical and without contaminants. Otherwise, the mixture melting point would be depressed below the estimated melting point and the range would be broader. TLC is another way to test the purity of the sample. As the TLC plate had three distinguished spots of compounds without smudges and multiple spots per compouns, again, indicating that there are no impurities in any of the analyzed compounds. In experement 2, the purification of the unknown solution was done through distillation. The plateau was reached at 56 Cº and that is when the solution was collected. However, a constant boiling point does not mean that the pure homogenous compound was collected. Gas Chromatography graph demostrated that the peak of the unknown compound is very similar to the peak of acetone, with retention times being very similar as well (1 min and 1.04 min correspondingly). There were no other peaks on the graph meaning that the solution was pure. However, the signal strength of acetone is twice as large as the one of the distilled sample. Height of each peak is in proportion to the amount of the particular component present in the sample mixture. Smaller signal value of my sample indicates that its concentration is smaller. The solution might got diluted with water during the distillation process as I took the erlenmayer flask with the compound out of the ice water bath.

6. Figure 5. Gas Chromatogram of the sample, acetone and isopropanol

Gas Chromatogram 1600 1400

Sample

Signal (mV)

1200 1000

Acetone

800 600

Isopropan ol

400 200 0 0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Time (minutes) 7. Common knowledge does not require citing. Usually, this in the information one on average considers reliable and does not need to look it up. For experiment 1, some statements about the filtration procedure can be considered common knowledge. For example, it is well known that a gravity filtration filters out insoluble materials out of the solution. The need to dispose organic waste in separate container, as well as the instructions not to look directly at the UV light bulb to prevent eye damage are common knowledge. However, specific information, like melting point values for caffeine, should be cited.

References (1) Combined Chemical Dictionary (CCD); [Online]; http://ccd.chemnetbase.com.uml.idm.oclc.org/faces/chemical/ChemicalSearchResults.xhtml (accessed 6 October, 2017). (2) Zajac, M. A., Zakrzewski, A. G., Kowal, M. G., & Narayan, S. (2003). A novel method of caffeine synthesis from uracil. Synthetic communications [Online] 33(19), 3291-3297. http://www.tandfonline.com.uml.idm.oclc.org/doi/abs/10.1081/SCC-120023986 (accessed 16 October, 2017). (3) Caffeine, MSDS No O1728-500 [Online]; J.T.Baker and Fisher Scientific: Fair Lawn, NJ, July 15, 2014. https://www.fishersci.com/store/msds? partNumber=O1728500&productDescription=CAFFEINE+USP %2FFCC+500G&vendorId=VN00033897&countryCode=US&language=en (accessed 20 September, 2017). (4) Luong, H. CHEM 2210 Introductory Organic Chemistry 1 Structure and Function Lab Manual, F18 Edition; University of Manitoba: Winnipeg, MB, 2017; 77. (5) Royal Society of Chemistry. ChemSpider. Acetone, CSID:175, http://www.chemspider.com/Chemical-Structure.175.html (accessed 25 September, 2017). (6) Royal Society of Chemistry. ChemSpider. Isopropanol, CSID: 3644, http://www.chemspider.com/Chemical-Structure.3644.html (accesses 25 September, 2017)....