Stoichiometry

lab report conclusion – IDENTIFICATION OF UNKNOWN WITH IR AND NMR

I will upload the manual. I just need conclusion explanation how I got the unknown I will also upload the picture of IR results and we just have to explain how we got that accordingly to the experiment explained in the manual. You have to explain what diffferent peks mean and accordingly to IR you have to explain how you identify the unknown and tell what unknown it is.

Chromatography (TLC) of an unknown mixture

Chemistry Assignment Help Microscale Flash and Gravity Column Chromatography, and Thin Layer Chromatography (TLC) of an Unknown Mixture
Prepared by Ryan Paul Cortez and Nadene Houser-Archield* (modified by S.N.Yasapala)
The Principles of Column Chromatography are similar to those of thin layer chromatography (TLC); however, TLC is typically used for identification purposes, whereas column chromatography is a preparative technique used to separate a mixture of compounds or to separate a compound from an impurity. Before you move to the next part please watch the videos provided below.
Principles of TLC
(https://www.youtube.com/watch?v=yig3QCfBTzc)
Click above link to understand the principles of TLC and how you can use the information from TLC to identify the components of a mixture (for qualitative analysis) and how to select a suitable solvent for column chromatography.
Principles of Column Chromatography
(https://www.youtube.com/watch?v=yig3QCfBTzc)
Click above link to understand theory of column chromatography. By watching the video above, you will learn how to pack a column, load a column with a sample, choose and use of an eluting solvent, and how to separate the mixture efficiently and minimize the contaminations (increase the purity of each component) during the separation process.
When performing a column chromatography, following basic steps are used;
Pack a vertical column with a stationary phase medium such as silica gel or alumina. Condition the stationary phase with a mobile phase; that mobile phase is the eluting solvent/solvent mixture. Load the sample onto the column; then, move it along, through the stationary phase by adding the mobile phase/eluting solvent. Polar compounds have strong attraction to the stationary phase and therefore move slowly down the column; whereas, nonpolar compounds, having little attraction to the stationary phase, move rapidly down the column. The more polar the eluting solvent, the faster all compounds will move down the column. The less polar the eluting solvent the slower all compounds will move down the column. In Flash Column Chromatography the eluting solvent is forced through the column via air or other gas pressure; this expedites the process; that is a flash separation is much faster than the corresponding gravity separation.Caution, the flash bulbs used in this experiment contain latex. If you are allergic, have your lab partner handle the bulb.In this exercise you are supposed to 1) separate a mixture of two unknown compounds, dissolved in a solvent, from one another by column chromatography and then 2) use TLC to identify the components. The components of the mixture could be acetophenone, benzoic acid, biphenyl, or methyl benzoate.

Flash Column Chromatography1) Dry pack the column (Pasteur pipet):a) Obtain a clean dry Pasteur pipet—from now on it will be called a “column”. Place it in a buret clamp (on a buret stand). Using the long stem of a cotton swab stuff a small cotton filter disc into the nose of the column. Please watch the following video (https://www.youtube.com/watch?v=jwXZ8O1Rf7I) and have a look on Figure 1 to get some idea about how to do “part a”.
Video may not explain an exact procedure what we are doing in the laboratory, but, it provides a very good idea about how to do the initial setting up.
Figure 1: Adding cotton filter disc into the nose of the column
b) Silica gel is a fine porous powder which can cause respiratory problems; in extreme cases it can cause silicosis (whose symptoms bear similitude to asbestosis). Do not breathe it in.Procedure for massing dangerous chemicals (in this case, 1 gram of silica gel): Stopper a 10mL Erlenmeyer flask. Mass the flask with the stopper on top. Calculate the mass you expect once the 1 gram of silica gel is added.
In the hood,
Add 2 – 3 spatulas of silica gel to the Erlenmeyer.
Re-stopper the flask.Wipe down the exterior of the flask with a dry paper towel to remove any silica dust.
Mass the stoppered flask, and contents.
Add or remove silica gel, and go through the process again until the total amount of silica gel in the flask is ~1.0 gram.
Using a waxed weighing paper, pour the silica gel into the column. Gently tap the sides until the silica gel has a level top.
c) Tare a waxed weighing paper and then add ~0.2 -~0.3 grams of sea sand to it. Pour the sand atop the silica gel in the column. Tap it down until the sand has a level top. Your set up should be closely similar to the figure2.
Figure 2: Column after filling silica gel and the sand
2) Obtain eluting solvent 1:To a 25mL graduated cylinder add hexanes (25mL).3) Condition the column:
Before adding the sample, it is very important to condition the column with eluting solvent to obtain optimum and reproducible results.a) Place a 25mL Erlenmeyer or a beaker beneath the column. Gradually, using a clean Pasteur pipet add eluting solvent 1 (hexanes) into the top of the column without disturbing the top of the silica gel (see figure 3). Fill the column to the top.b) Let the solvent drip from the column into the Erlenmeyer until the solvent level is approximately 1cm above the top of the sand. Fill the column again. Let the solvent drip into the Erlenmeyer until the solvent level is 1cm above the top of the sand. Fill the column a third time; let the solvent drip into the Erlenmeyer until the solvent level is just below the surface of the sand, but not below the top of the silica gel.
Figure 3: Conditioning the column
4) Shake the bottle of unknown mixture to promote homogeneity. Using a Pasteur pipet, obtain ~0.25mL of the unknown mixture assigned to your group. Remember, it is two compounds dissolved in a solvent.5) Loading the column: Load the ~0.25mL of solution from the Pasteur pipet onto the surface of the sand in the column (see figure 4). Let the Mixture go just beneath the surface of the sand; then, add 1-2mL of eluting solvent 1 (hexanes) to the column via pipet. Let the solvent drain just below the top of the sand. Again, add 1-2mL of eluting solvent 1 to the column via pipet. Let the solvent drain just below the top of the sand. NOTE: You may not see any color of the sample if the mixture does not contain a colored compound.

Figure 4: Loading the column with sample

6) Running the column: By flash, be sure not to attach the flash bulb to the column—this would lead to difficulty in controlling the pressure and sucking the silica and sand out of place.a) Place a 10mL receiving beaker or 10mL Erlenmeyer flask, labeled “1”, beneath the column. Fill the column with eluting solvent 1 (hexanes).b) Flash the column until the solvent is ~ 1 cm above the sand. That is, place a flash bulb above the column/Pasteur pipet; squeeze the bulb in order to force air into the column. The solvent will move rapidly down the column (see figure 5).

Figure 5: Running the column
i. Refill the column and repeat the process until ~5mL of the eluted solvent is collected in receiving flask/beaker 1.ii. Change to another receiving vessel labeled “2” and flash until another 5mL of eluted solvent is collected.iii. Repeat this process with receiving vessels 3, 4, and 5 (see figure 6).
Figure 6: Collecting the fractions
c) Place receiving vessel 6 beneath the column. i. Fill the column with isopropyl alcohol or ethanol (eluting solvent 2). ii. Flash the column with eluting solvent 2 (alcohol) until ~ 5-10mL elutes.
Then run a column by gravityFollow the same procedure for flash (as above) but do not flash the column; simply let it drip by gravity.
7) Identify fractions that contain components of the mixture (Be sure not to mix up your flash fractions with your gravity fractions):a) At the station setup by the instructor, make sure no organic solvents or other flammables are nearby. Make several micropipets from capillary tubes (open on both ends), using a Bunsen burner.b) Using micropipets, spot a portion of each fraction onto a TLC plate to determine which fractions (1,2,3, etc.) contain components of the mixture. Each of the possible unknowns has a UV active chromophore that will fluoresce under a short wave, 254nm UV lamp.
8) Analysis of fractions that contain UV active components:
Before you read the next step of the procedure, please watch the following video to be familiar with how to run a TLC plate to identify components of a mixture.
How to run a TLC plate in the laboratory
(https://www.youtube.com/watch?v=qdmKGskCyh8)
a) To a 10mL graduated cylinder add 8.5mL of hexane and 1.5mL of ethyl acetate (EtOAc). Pour this mixture into a TLC developing chamber (a beaker wider than your TLC plate). Cover the chamber with an inverted watch glass.b) Obtain two TLC plates. Check them under the UV lamp for cleanness and for the presence of indicator (they should glow under the UV light). Do not look directly into the lamp light! It will damage your eyes. Using a pencil (not a pen!) draw a horizontal line ~1.5cm from the bottom of each plate.
c) Spot a plate with each fraction from 1 through 6 that had components from the mixture. Below the pencil line, label the spots “1”, “2”, “3”, etc. Take the TLC.
(You may choose to clean and reuse your micropipets as follows: wipe it off with a kimwipe; touch it to a kimwipe to empty it of its contents; dip it into clean EtOAc (in a small beaker or flask) and then touch it to the kimwipe to empty it; do this several times.)
d) Without splashing place the spotted TLC plate in the developing chamber (tweezers might be helpful). Put the watch glass back on top. Allow the plate to develop until the solvent front is between 1 – 1.5cm from the top of the plate. During development, do not bump the table or otherwise cause movement in the developing chamber.
e) Pull the plate out of the chamber (tweezers might be helpful) and immediately trace the solvent front with a pencil. Examine the plate under a UV lamp. Circle/trace all spots.
f) Calculate the Rf value for each spot on each plate.
g) Combine like fractions (fractions with the same Rf value) that are pure (a pure fraction will have only one spot in its TLC). At this point, you should have two pure fractions. Set aside any impure fractions.
h) Spot a plate with the known solutions (these are already mixed for you) and the two unknown fractions. Check the spots under the UV lamp; if a spot does not show up as a fluorescent purple dot or if it is too light, re-spot it.
i) If a component is a solid obtain the melting point.j) If a component is a liquid take the IR spectrum.Save your TLC plates. You will tape them to your lab report.
7) Clean up:a) In the hood, tap the contents of the column into the designated waste container.b) Follow normal cleaning procedures.
Sample Data
Given below are the sample data you would have obtained if you performed this lab in the laboratory. Rf value for each pure compound (under same experimental conditions) of the mixture is also given for your comparison.
Mixture/fraction
Distance traveled by solvent front (cm)
Distance travelled by each spot (cm)
Known (spot 1)
5.5
0.1
Known (spot 2)
5.5
2.3
Known (spot 3)
5.5
3.5
Known (spot 4)
5.5
4.2
Unknown (fraction 2)
5.5
4.1
Unknown (Fraction 4)
5.5
1.9

Compound
Rf value
Benzoic acid
~ 0
Methyl benzoate
0.62
Acetophenone
0.40
Biphenyl
0.77

Post Lab Questions for Flash Column Chromatography and TLC Report:
1) Fill in the chart below for each known, and for each solvent.
Structural formula:
Line structure:
2) Data table containing all Rf calculations for knowns and for fractions. Identification of each spot3) Why it is necessary to trace your TLC plates (of the knowns and of the fractions) into your notebook?
4) Rank the knowns in order of increasing polarity according to their Rf values.5) Of the solvents ethyl acetate and hexane, which is most polar? Briefly explain6) What would you expect to see if pure hexane had been used to elute the mixture in the column and/or the TLC?7) What would you expect to see if pure EtOAc had been used to elute the mixture in the column and/or the TLC?8) Describe the stationary phase a) in TLC b) in column chromatography.9) Describe the mobile phase a) in TLC b) in column chromatography.10) Which of the compounds below should be UV active? In the space below the table, briefly explain
a)
b)
c)
d)
e)
f)
11) Which type of compound a) polar or b) nonpolar is most strongly adsorbed by the stationary phase of a column or a TLC plate? Briefly explain.12) Why is it not feasible to analyze benzene by TLC?13) Suppose the following were a mixture of compounds and no chemical reactions took place among them. Place them in the order in which they would elute from a column (first compound to exit the column to the left, last compound to the right): R2C=O, RCO2H, R(C=O)H, RBr, RCO2R, ROR, R2C=CR2, ROH, RH14) Place the following solvents in order of decreasing eluting power: hexane, ethanol, acetone, ethylacetate, water, toluene, carbon tetrachloride, dichloromethane, propan-1-ol, diethyl ether. (If you are not yet proficient with polarity concepts, dielectric constants might be helpful (use the CRC)).15) In TLC, why aren’t liquid samples spotted pure/at their full strength; i.e. why are they diluted?
Reference
https://orgchemboulder.com/Technique/Procedures/Columnchrom/Procedure.shtml

In what ways does chemistry affect your life? Discussion Board

In what ways does chemistry affect your life? Hint: allergies are caused by particles called allergens in the air or that are contained in other substances. Also remember, you are using chemistry in the kitchen. How else does chemistry play a role in your everyday activities. Reply to discussion question should be 150 words or more and response to another student at least 100 words.
If you use an outside source for material, don’t forget to give a citation and reference. Here is a link that will help you : https://owl.purdue.edu/owl/research_and_citation/apa_style/apa_formatting_and_style_guide/in_text_citations_the_