Lets talk about Lab Techniques - Chromatography

ChromatographyHello gorgeous people...

In case you weren't aware there are several different types of chromatography that are commonly used that separate (aka extract aka resolution) compounds based off subtle differences in properties including polarity, size charge and/or affinity for other compounds.

Examples include....

• Column (Flash) Chromatography
• Gas Chromatography
• Gel Filtration
• Ion Exchange Chromatography
• Thin-Layer Chromatography (TLC)
• Affinity Chromatography can be done but these beads are uber modified ie antibodies for a virus or a bead with a particular DNA fragment and in reality I can't explain the general concepts behind these because it would take too long. Just know its anything you want anyway you want and your beads fish out whatever you seek.

I'll spend some time delving into each.....

You may ask why bother when I can wiki this?

This is true but I'm going to try to make this user friendly so everybody can understand. Plus now you don't have to switch tabs every 5 seconds. I'm just trying to help....By the way and as always PLEASE click an ad if you like what you see. It helps me out so I can continue to keep helping you all out!

Column Chromatography

I'm lazy and colum chromatography will be explored in further detail in the description of Gel Filtration Chromatography and  Ion-Exchange Chromatography...

I'm just gonna say that it would probably be a good idea to know that its a pretty decent way to separating bulk compounds. It involved filling a column up with silica gel (just like the silica of the TLC plate yes, SiO2). In this case you would have a polar stationary phase because those silica beads aren't going anywhere and a non polar mobile phase gets poured through this column that has been packed with the polar silica beads.

Main concept behind how this works: Like associates with like. The polar stuff will stick the polar beads. The non polar stuff will stick with the non polar mobile phase and be repelled by the polar beads it will go through the column without interacting with the polar silica beads....As I said the like will associate with the like. Polar with polar non polar with non polar...This all occurs in a column....hooray!

Gas Chromatography 

Lets be honest Gas Chromatography is kind of rare and in reality you/me/we probably won't be using it all that much in our scientific careers. In Gas Chromatography the liquid is the stationary phase and the gas is the mobile (moving) phase.  The ultimate goal is still to separate components and the main characteristic you'll use is their differences in volatility. Remember highly volatile means its boils easier or at a lower temperature. 

Fun Fact: Gas Chromatography has proven to be particularly useful for stuff that's super volatile

The procedure consist of loading a sample into a syringe and injecting it into sample port of the chromatography machinery/device, it then passes into the column which is under 24/7 temperature control.  The sample is vaporized and carried by an inert gas (usually Helium). The more volatile the component the less it will interact with the stationary phase so it can travel faster through the column (ie it finishes traveling first). As the components come out of the mixture a detector detects them (the identity of the component and the amount are recorded) and reports to a computer that usually puts it into some sort of visual form. This visual form can be integrated kind of like NMR to determine the percent of the compound the component was. Luckily enough we live in an age that the computers can do all the math and present the rentention times.

Note: The detector usually has a flame portion that helps in the process of detecting. The components pass through the flame become ions that affect the electronegativity. Detectors can also aid in the process of mass spectroscopy to aid in the process of Mass Spectrometry, this is called Gas Chromatography Mass Spectrometer (GCMS).

Gel Filtration Chromatography

Gel Filtrationis a type of Column Chromatography. The main physical attribute it uses to separate components is that of size.  It can be thought of as a molecular sieve and is sometimes/also called size exclusion chromatography.

You may ask, what is used to control the sizes of compounds that will be selected for?
The answer is actually pretty simple "beads" made of cross linked dextran. Dextran is a polysaccharide that is insoluble in water. The amount of cross linking determines what can pass through based on how porous it is. More links = more tangled = smaller pore sizes. Like the story of goldielocks and the bears a compound can either be too big, too small or jusssssttttt right.

The degree of porousness is commonly referred to as the fractionation range.

 For example Sephadex G-25 beads have a fractionation range of 1000–5000.

Size	What will happen and why?
<1000 g/mol	These molecules are small, and in this case they're too small. They can freely enter and exit the pores as the wish they will come out entirely in the total volume because of this freedom.
between 1000-5000 g/mol	Anything in this range will come out between the void volume (discussed below) and the total volume (also discussed below). These beads are in the right size to enter the matrix created by our lovely porous beads....aww how nice, no? In general it is said that... k (log molar mass) = Elution volume divided by the Total Volume You may ask what does this mean...It means that the volume in between the void and total is thought to be directly related (proportional) to the log of its molecular weight. The elements are separated by size and that equation shows the relationship between their size and the volume in which they eluted.
>5000 g/mol	Anything 5,000 g/mole or greater in size will be toooooooo big to actually go through the pores of the beads. Being that it can't enter the matrix it bypasses it and it is through the be excluded from the beads. As a result the stuff that is too large elutes (leaves) first and is said to be found in the void volume of the column.

Terms and other stuff that you should consider knowing: 

• Total Volume of column = Void Volume + Internal Volume
• Void Volume = volume outside the beads
• Internal Volume = Volume occupied by the beads
• k (log molar mass) = Elution volume / Total Volume

Ion Exchange Chromatography 

Ion Exchange Chromatography involves the separation of molecules on the via their charge. In reality these is pretty much a modified version of gel filtration using modified/custom beads that have specific/chosen characteristics. There are two broad categories Anion and Cation Exchangers.

Anion Exchangers:

Often involves Diethylaminoehtyl dextran because of its overall positive charge.

Anion exchangers contrary to what you would guess actually have a positive charges. Due to their positive charge they bind to molecules with an overall negative charge. Meaning molecules that are positively charged and/or neutral can pass right on through well strictly speaking that is still based on their size and the pore size also known as the fractionation range.

Cation Exchangers :

Often involves CM Sephadex = carboxy methyl sephadex, has an overall negative charge.

Like anion exchangers the name can confuse you but yet again contrary to what you would expect they have an overall negative charge allowing them to bind with cations (molecules with positive charge). The Negative and Neutral stuff pass right on through at a rate determined by the good old fractionation range.

Both Anion and Cation Exchangers play with the idea of charge affinity. In order to separate what has bound to the beads additional mobile phases are added that vary characteristics like salinity or pH that will take the position on the beads kicking off the stuff that was previously bound to it. The get "exchanged" hence the name.

You can think of it like the increased anion or cation concentrations in the mobile phase compete with the previous compound that was bound to it. That compound gets kicked off, eluted and you collect it. This method is extremely sensitive and it must be done in the right order with proper timing or else you don't get the desired separation.

Thin-Layer Chromatography (TLC)

Thin-Layer Chromatography has already been mentioned in the experiment so for funsies feel free to go here to learn about the Purification of Caffeine.

But it can't hurt to talk about it a little bit more.

Thin Layer Chromatagraphy once again allows for separation based on polarity. You get have a polar stationary phase that is the silica plate which is coated with a thin layer of which is an absorbant silica (SiO2) and a non polar mobile phase.

 You carefully spot your sample and some sort of comparison or known compound at the origin of the plate. You should probably mark it with a pencil or something. You then place the plate in the stationary phase which is usually in a beaker which is covered with aluminum foil to prevent evaporation of the mobile phase. You let the sample run technically known as developing the plate till the solvent gets really close to the top of the plate.

Note that Capillary action is the "force" and/or "reason" that draws the nonpolar mobile phase up the plate.

When the plate has fully developed quickly mark where the solvent reached so you can calculate the ratio to front, also known as the beloved Rf value.

Before you do any calculations know that the more polar components have stronger interactions with the polar plate and are less likely to move with the solvent, well that is in comparison to nonpolar components that are more likely to travel with the nonpolar stationary phase.

Long story short the more like the stationary phase the component is the more it will travel.

To Calculate the Rf Value do as follows.

Divide the distance that the compound traveled from the origin by the distance the solvent traveled. Units don't really matter because they will cancel out, but I personally like centimeters.

Semi Important points...

• Rf values should never be greater than 1. Why? Well, because its impossible and the compound couldn't actually travel further than the solvent. 
• The closer to 1 the Rf value is the more the component was like the stationary phase.
• The Rf value will always be positive. Why? Well, because there is no way to get a negative value, however you can get Rf values that are very close to 0 if the compound didn't move.

Paper Chromatography

Such thing exists and in reality it follows the same rules as long as the mobile phase is not polar and the stationary phase is polar.  usually is the opposite of TLC discussed above. Unless the polar and non polar components are switched.

Rf values are calculated in the same fashion with the same implications.

The paper is usually composed of some sort of polysaccharide with copious amounts of OH groups (making it polar)

 

Synthesis of Butyl Benzoate

Intro

The purpose of this experiment was to explore the methods by which a phase transfer catalyst facilitates the synthesis of the ester Butyl Benzoate from Sodium Benzoate and 1-Bromobutance. The full balanced molecular equation for the synthesis is NaC₆H₅CO₂ + CH₃CH₂CH₂CH₂Br -> C₆H₅CO₂CH₂CH₂CH₂CH₃ + NaBr.

How was it done?

First sodium benzoate was placed into a round bottom flask containing H₂O. Next 1-Bromobutane, a boiling stone and Aliquat 336 were added to the same round bottom flask. The round bottom flask was fit with a reflux condenser and was set into a heating mantel attached to a variac set at 45%. Note the joints of the glassware were greased while keck clips and clamps were used to keep the glassware upright and stable. The mantel should be turned on and allowed to run for an hour under reflux conditions.

            After an hour the round bottom flask was removed from the mantel and cooled in room temperature water. The cooled contents were transferred to separatory funnel and the flask was rinsed with dichloromethane, which also went into the funnel. An additional 10 mL of dichloromethane were then added to the separatory funnel. The funnel was gently swirled and inverted the opening the stopcock to release pressure. The mixture was allowed to sit in a ring stand until 2 layers were visible.

            The lower organic layer was drained and placed into a clean labeled Erlenmeyer flask. The aqueous layer was poured out the top and placed into another clean labeled Erlenmeyer flask. The organic layer was transferred back into the separatory funnel where it was washed wit 5 mL of 15% NaCl solution. The lower organic layer was placed into the appropriate Erlenmeyer. Next anhydrous sodium sulfate was added to the Erlenmeyer with the lower organic layer (containing the ether) and was allowed to sit for 15 minutes.

            Meanwhile a 25 mL Erlenmeyer was washed, dried and weighed and Pasteur pipettes were fitted with cotton and prepared (shown left). The Pasteur pipette was used to transfer the organic solution into the newly cleaned Erlenmeyer.

            Next the dichloromethane was removed via a stream of nitrogen air while in a warm water bath.  Measurements of the weight of the beaker with contents were taken till two consecutive measurements are within .03 grams within one another. Once the weight was in the appropriate range the product was prepared for IR and checked for evidence of the product.

Results, Questions, Calculations and stuff like that...

Limiting reactant: There is a 1:1 molar ration of 1-Bromobutane to Sodium Benzoate. The experiment used 2.0 mL of 1-Bromobutane with density 1.27 grams / mL = 2.54 grams of 1-Bromobutane. Compared to the 3.05 grams of sodium benzoate. Hence 1-Bromobutane is the limiting reagent.

Theoretical Yield

__g 1-Bromobutane x 1 mole 1-Bromobutane x 1 mole Butyl benzoate x 178 grams   =  ____ g Butyl benzoate expected

                                    137 grams                  1 mole 1-Bromobutane    1 mole Butyl benzoate

  

Percent Yield

Observed yield     x 100%  = ______%

Expected yield   

 

Infrared spectroscopy absorption bands of significance

Major Absorption peak or band	Suggested reason for peak	Functional group
Strong peaks near 1600 and 1500-1430	C6H5  Benzene ring	Benzene ring
Activity between 1602 and 1782	C=O	Carbonyl
Strong peaks between 1070 and 1274	C-O	Ether
Strong peaks near 2850-2959	C-C-H	Carbon Hydrogen stretching vibration

Carbon-13 Nuclear magnetic resonance imaging results

Peak in ppm	Significance
13.8345	Methyl (CH3)
19.3615	CH2
30.8584	CH2
64.8986	C-O
76-77	CDCl2
128.3910	Aromatic Carbon
129.6049	Aromatic Carbon
130.6125	Aromatic Carbon
132.8722	Aromatic Carbon
166.7674	C=O

Proton Nuclear magnetic resonance

Approximate ppm	Splitting	Integration	Group Significance
.99	Multiplet	3	CH3
1.4	Multiplet	2	CH2
1.7	Multiplet	2	CH2
4.3	Triplet	2	CH2 expected to be near electron withdrawing group
7.4	Multiplet	2	In monosubstituted benzene ring
8.0	Multiplet	2	In monosubstituted benzene ring

DEPT analysis

Approximate Peak location ppm	Positive or negative region	Potential significance
11	Positive	CH3
29	Negative	CH2
64	Negative	CH2
128	Positive	CH most likely in aromatic region
130	Positive	CH most likely in aromatic region
132	Positive	CH most likely in aromatic region

 

As indicated by Infrared spectroscopy it is clear that the yielded product obtains a Benzene ring and has activity in regions associated with carbonyl and ether functional groups. The data from the Infrared spectroscopy also suggests that there is a carbon chain in the product. The data from the Carbon 13 Nuclear magnetic resonance imaging results suggests that there is a Carbon double bond with oxygen (C=O) and a Carbon Oxygen single bond (C-O). Absorption peaks near 130 ppm indicate Carbons in an Aromatic ring while the more upstream peaks suggest the presence of CH₂ and CH₃ most likely in a Carbon chain. Proton Nuclear magnetic resonance and DEPT analysis suggest a monosubstituted benzene ring is in the product and the presence of multiplets in the spectrum suggests that there are neighboring unequivalent Carbons attached to hydrogen and suggests electron withdrawing groups that increase deshieleding. Overall data collected from the spectra support the expected result of Butyl Benzoate being synthesized from 1-Bromobutane and Sodium Benzoate via use of the phase transfer catalyst.

 

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Color and Para Red

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In this post I'll talk about a little chemistry regarding color(s) and Synthesis of the Dye Para Red from Aniline

First some info from WIKI:
Para Red (paranitraniline red, Pigment Red 1, C.I. 12070) is a chemical dye. Chemically, the dye is similar to Sudan I. The dye was discovered in 1880 by von Gallois and Ullrich, and was the first azo dye. It dyes cellulose fabrics a brilliant red, but is not very fast. The dye can be washed away easily from cellulose fabrics if not dyed correctly. Throughout making Para Red, the solution will become acidic and basic. Small amounts of byproducts may be left over after the Para Red dye is made that may be acidic or basic, but if made correctly there are little of these and the byproducts have no effect.
In the United Kingdom, the dye is not permitted in food. The UK's Food Standards Agency (FSA) stated that "the Agency’s independent scientific experts have advised that, although there are very limited data available, it would be prudent to assume that it could be a genotoxic carcinogen". ^[2]
On 21 April 2005, the FSA announced that some batches of Old El Paso dinner kits had been contaminated with the dye, and issued an alert.^[2] Also, reported on the 5 May 2005, the dye was found in 35 products which have now been taken off supermarket shelves. The products were mainly cooking sauces, though some are also spices.^[3]

At this point I'm going to ask you please please please yo help me out and check out these sites below if you appreciate the help here! 

Procedure

             All procedures were carried out under a hood, all individuals involved wore nitile gloves and safety goggles. Glassware was cleaned, rinsed with deionzed water and if necessary acetone before usage.

            First .7 grams para-Nitroaniline, 15 mL H₂O were placed in an Erlenmeyer  flask. The flask was placed onto a hot plate and 3 M HCl was added till everything was completely dissolved. Upon dissolving the solution was cooled in ice water bath (0-5°C) for 10 minutes. Meanwhile a solution of 7 % NaNO₂ was prepared by adding .7 grams NaNO₂ to 10mL H₂O and swirled for 10 minutes with stir bar via the use of the stir function on the hot plate. The heating function was turned off on the hot plate and the solution was kept cool during the period of the stirring.

            Next .7 grams KI were weighed and placed in a beaker. Via the use of a pipette 5.0mL of the cold diazonium salt was added to the KI. The mix was swirled till gas evolution decreased and then ceased. The solid was isolated via vacuum filtration with a Hirsch funnel and washed twice with 1mL portions of cold deizonized water. After filtration the product was isolated and kept for a week allowing it to dry.

            In another 50 mL beaker .25 g b-naphthol and 15mL water were heated till about 60-80°C. Next 10% NaOH was added drop wise will all was dissolved. Meanwhile a notch was cut in the wool portion of the fabric (to help with identification). The fabric was soaked in the solution for about 2 minutes, then removed with forceps and patted dry. The fabric was then placed in the cool diazonium salt.

            Once the fabric was removed the remainder of the b-naphthol was chilled till about 5°C. After cooling the remainders of the 2 solutions were mixed together and via the use of a Buchner funnel underwent vacuum filtration. The collected product was washed thoroughly with water. Once the product was collected it was placed in a beaker and allowed to sit for a week to dry. After the products dried the melting point range was observed and analyzed

For more go here:

https://docs.google.com/viewer?a=v&q=cache:lravLKFHs34J:ochemonline.pbworks.com/f/04_Azo_Dyes.pdf+&hl=en&gl=us&pid=bl&srcid=ADGEESglnTd8VLb0HroH3tQxK2VX1Fqbdyj_WYOKBfIA2Uvw5Gq-VdBtjmuoJJu6eHNr-uqF0-0DssQbyG2VMXEdm2HHPlQKX2Cvoy3MWk5AJZ9mzEiCRfntPakhtnKTtvC8woqy3GdW&sig=AHIEtbSwxqlxEJSBGwZDfD6wYRa-rKJXYg&pli=1

So you have a chemical unknown...

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Feel free to try this out if you have a chemical unknown it might help!

Welcome to the Organic Compounds Database.

This 2483 compound database has been compiled by Harold M. Bell at Virginia Tech. Fill in the form below with as much information as you can. Leave the information blank if you don't know or you don't care. Click on the submit button to execute your search. You will receive at most 20 hits.

Melting Point +-5C________________ Boiling Point +-5C
Index of Refraction, nD20 +-0.005_ Molecular Weight +-2amu
Formula: C H N O Cl Br I S
(for formulas you can enter a ">" or "<" in front of the number, eg. >2)

UV Absorption Wavelengths:

, , +-5 nm

Mass Spectral Peaks:

, , , m/e

Chemical Types:

No Carbonyl present_ Carbonyl present
No Aromatic present_ Aromatic present
No OH or NH present OH or NH present
CH type:
no C-H saturated C-H unsaturated C-H both saturated and unsaturated C-H Compound name contains:

Key to the Literature References
This data is available with 2D-structures and NMR chemical shifts in ISIS/Base format.

Bromination of trans-cinnamic acid

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In this lab we'll look at what its like to add bromine to transcinamic acid via adding methods of stereo-chemistry. Additionally we'll take a look at trying to prove the reaction was successful and that we actually did get 2,3-dibromo-3-pheylpropanoic acid.Bromination are a type of Halogenation procedures using bromine, read more about it here.





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 Below is kind of a generalized look at the addition of the Bromine via a Trans Addition, which sorry to spoil the surprise is the way its going to add.

Trans-cinnamic acid (E-3-phenyl-2-propanoic acid) has a molecular weight of 148 g/mol and a melting point of 133 degrees Celsius.

There are several enantiomers of 2,3-dibromo-3-phenylpropanoic acid, they all have a molecular weight of 308 g/mol (Molecular Weight: 307.96662 to be specific).

The (2R, 3S) and (2S, 3R) have a melting point of 202-204 degrees Celsius.

The (2R, 3R) and (2S, 3S) have a melting point of 93.5 to 95 degrees Celsius.



 Things that were done:

150 mg trans-cinnamic acid and .6 mL glacial acetic acid were put acid in a test tube. The tube was put in a 50 degree celcius water bath till all the trans-cinnamic acid dissolves. Next 1.0mL of 1.0M Br2 in acetic solution. the mix was stirred via agitation at 50 degrees Celsius till the color faded from red/brown to light orange and was heated for another 15 minutes. Next a drop of cyclohexane was added. The mix was cooled in ice water bath for 10 minutes (crystals formed). Meanwhile distilled water was cooled (in an ice bath). Note if the crystal didn't form the side would have been scratched with a siring rod and left in the ice water bath for another ten minutes.

The product was collected via vacuum filtration. The crystals were washed with ice water ( note its a good idea to do it till the smell of acetic acid is gone. Next was the process of recrystallization. The sample retrieved from vacuum filtration was placed in .5mL ethanol in an 10mL Erlenmeyer flask. After the sample had dissolved boiling stick was added and the mix was heated via a steam water bath. If the sample doesn't dissolve add more ethanol. Next a volume of water equal to the amount of ethanol was added. The sample was removed from the heat and allowed to cool for 10 minutes in ice. Crystals were removed from the solution via vacuum filtration (note a new clean Hirsch funnel and new filter paper was used)

 Things you may ask...

What is a mixed solvent recrystallization? What is the reason for using mixed solvent recrystallization?

 Mixed solvent recrystalization refers to a process of crystallization used for the purpose of purification. A solvent is added to a mixture with desired and undesired components creating a solution. The solution is heated so that all of its components are able to dissolve, this solvent chosen because of its known properties of solubility. At a higher temperature everything should remain dissolved in the solvent as it becomes supersaturated. However as it cools crystals of your desired compound should form being that at lower temperatures the solvent can no longer remain super saturated, meanwhile impurities and undesired compounds should remain dissolved in the solvent. In this experiment the crystals could be isolated via vacuum filtration.

 Should the product exhibit optical activity?

 No the product would not exhibit optical activity because while each enantiomer is chiral they exist as a racemic mixture such that the specific rotation of one enantionmer would cancel the rotation of the other being that they should have the same magnitude but in the opposite direction.

 What is the mechanism of the addition like?

It can happen via a concerted mechanism (Shown below)

It can happen via Radicals

What can the melting point/range say about the purity of the sample?

 If the observed melting point or range is near the reported melting range from the literature it suggests that  the product is that of the enantiomer set. For this particular experiment the  (2R,3S) and (2S, 3R) enantiomers of 2,3-dibromo-3-phenylproanoic acid are expected. Indicating that the bromine addition occurred via an anti method. Had bromine of added via syn addition the melting point would have been near 95 °C (provided in the literature).  The difference of several degrees between the literature and the experimental values may be the result of impurities and the possible existence of other enantiomers or compounds in the product. Recall that impurities cause depression and extend the range of the melting points.

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Meet Metta World Peace formerly known as Ron Artest.

 Shall we go to Paradise?

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Some more attempts at funny.

Limonene

Limonene exists in R-(+) and S-(-) formations. Both have a boiling point of 175.5-176 degrees Celsius, both have a molecular weight of 136.2 grams per mol but they differ in their optical rotation. 

R-(+) has a density of about .8402 g/mL and an optical rotation of 125.6 degrees (note the positive number) while the S-(-) has a density of .8407g/mL and an observed optical rotation of -122.1 degrees (note the negative number)

In this lab we'll talk about Isolating the R-(+) formation of Limonene from orange peels. Note the R-(-) can be found in Caraway seeds.

How you do it?
Take the oranges and peel them. It's best to do this right away to prevent the loss of limonene. Try to remove the white pulp from the peel.

In a blender add the peels and 200- 250 mL of water. After blending put in a 500 mL round bottom flask. Add 4 drops of anti foaming agent...or don't if you would like to have a "fun time". With a Claisen adapter prepare for steam distillation with a 50 mL round bottom flask as the receiver. Marking the 50 mL round bottom flask at the 35 mL level will be helpful so pour some water in it, mark it, empty it and voila.

Boil the mix without letting any solid material bump over into the condenser. Collect 35 mL of the distillate. Note if you use a heating mantel a variac will probably be a good idea as to add an element of control. Also it will prevent the mantel from heating up to quickly/getting to hot and in the process you may actually end up burning your orange peels. Burning the orange peels may result in bad results and a load of gunk that accumulates on the bottom of the round bottom flask which take my word will be annoying and nasty to clean up however a bit of acetone, some soap and some time will help you eventually make it clean again. Also the burned peels may affect your observed optical rotation adding an element of impurity to the sample.

Pour the distillate into a separatory funnel (125 mL size should do). Add 5 g sodium chloride and shake. Next add 10 mL dichloromethane via a conical funnel through the top of the separatory funnel. Gently shake the mix and allow for pressure to be release by opening the stop cock every so often. Let the mix sit and the layers to separate. Make sure the stop cock is closed during this process and the stopper is held is place or else by by sample.

Collect the bottom layer (the organic bottom layer and the top is the top aqueous layer) in a flask. Repeat the extraction with 15mL dichloromethane (fresh) every time. Next dry the extracted solution with anhydrous magnesium sulfide for 10 min.
Meanwhile weight and clean an Erlenmeyer flask for later use. Into this Erlenmeyer with the use of a conical funnel fitted with filter paper and pour the solution. This should take out the anhydrous magnesium sulfide.

Then by any means you want be it nitrogen gas, hot water bath or just allowing it to sit allow the dichloromethane to evaporate.

To do polarimetry (link should take you to wikipedia) obtain 10mL of 95% ethanol. Dissolve Limonene in 3 mL of the ethanol via Pasteur pipette. Transfer to a 10mL volumetric flask and do polarimetry on it. Note calculate the polarimeter with the 95% ethanol as the reference solution. The rotation should tell you about entantiomeric excess if applicable.

Questions:

 What is a steam distillation?  Why is it useful in this isolation experiment?

            Steam distillation is a form of distillation often used to distill heterogeneous mixtures. It allows for the adding of pressures of components in the mixture to overcome that of the atmosphere and boil. This typically results in lower temperatures till boiling is reached especially so when compared to a solution that follows Raoults Law.

            Steam distillation is useful in this experiment because it lowers the temperature necessary to give rise to the boiling of limonene. Typically to achieve this point the boiling point would be so high the orange peels would burn and the charring would contaminate the isolated limonene. The H20 and limonene pressures combine give rise to the lowered boiling point. It’s also possible that higher temperatures would result in decomposition of limonene.

 What was the purpose of the extracting of our collected distillate with dichloromethane and salt-water?

            The salt in the salt water allows for more transfer of limonene to the organic layer. The salt is absorbed in the water and saturates it decreasing the total possible amount of limonene that can be absorbed by the water. Similar to a process called "salting out".

            If the dichloromethane was used for extraction the Limonene would have been found in this layer. Because dichloromethane is more dense than water and they do not mix the dichloromethane would have formed a visible layer below the water that could be taken out by opening the stop cock of the separatory funnel and allowing the bottom layer to be collected.

How do I find the specific rotation?

specific rotation = observed rotation                                                                       
                               (density in g/mL) x length of polarimeter tube in decimeters

Or in words its the observed rotation divided by the product of the density (aka concentration) and the length of polarimeter tube in decimeters.

What happens if you shake too vigorously during the extraction with dichloromethane?

The gas could explode due to the build up of pressure inside of the separatory funnel. Also you may mix the layers so well that it won't separate as quickly.


On the other hand what happens if you don't shake vigorously enough?
The layers may not separate and limonene may not separate from the aqueous layer and go into the dichloromethane layer.

As always I don't get paid for this so if you can please join below I really appreciate it.