Organic Lab 1250 Midterm notes
Organic Lab 1250 Midterm notes CHM 1250
Popular in Organic Chem 1 Lab
Popular in Chemistry
This 7 page Study Guide was uploaded by Neha Bhagirath on Monday June 20, 2016. The Study Guide belongs to CHM 1250 at Wayne State University taught by Matti in Spring 2016. Since its upload, it has received 20 views. For similar materials see Organic Chem 1 Lab in Chemistry at Wayne State University.
Reviews for Organic Lab 1250 Midterm notes
Report this Material
What is Karma?
Karma is the currency of StudySoup.
You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!
Date Created: 06/20/16
Waste Management Used pipettes go in the glass trash Hazardous waste is never poured down the drain Acids Bases Halogenated organic waste Should not contain visible amounts of water Nonhalogenated organic waste Should not contain visible amounts of water Transition and heavy metals The tags on the boxes should be labeled using full chemical names and NOT formulas Liquid containers must be kept in secondary containers and always capped Solid waste goes in buckets Nothing other than broken glass should ever go in the broken glass container Mercury thermometers are hazardous waste Recrystallization Purpose: to purify organic solids. You are given an impure sample of unknown organic solid. Objective: Purify the solid by recrystallization, identify it by MP. (Start with impure crystals, dissolve in hot solvent, and get pure crystals back.) Procedure: 1) Choose a solvent that does NOT dissolve the compound when cold but does so when near boiling. Place 2 grams of the unknown in a flask and dissolve with a MINIMUM amount of boiling water using a hot plate. A dark oil may form in the solution because of insoluble impurities in water (if an oil forms, it is called “oiling out” and happens when a compound melts near the BP of the solvent being used.) More solvent may need to be added to fix this. Note: add hot water (solvent) to the solute, NOT the solute to the solvent. 2) Let cool a bit, then add 0.5 grams charcoal to remove colored impurities by adsorption to charcoal (charcoal is decolorizing carbon); (future recrystallizations do not NEED charcoal.) Do not add the charcoal to the boiling solution, it will boil over. Never add a solid substance to a solution AT or NEAR its boiling point. 3) Heat solution to boiling again, then filter by gravity WHILE HOT through PREWARMED funnel and FLUTED filter paper while hot (hot filtration.) This is the most important step to filter by gravity while hot. This is for the insoluble impurities present such as charcoal. The filter paper is fluted to increase surface area and allow for quicker filtration. Note: when you want the filtrate, use gravity filtration. 4) The clear filtrate is then cooled in air and an ice bath; crystals will form. If they don’t, scratch the sides of the glass container below the solvent level, with a stirring rod, making an uneven surface for crystal formation; or add a seed crystal; or concentrate the solution because you probably used more than minimal solvent (water.) 5) Collect crystals by suction filtration to isolate the compound. Dissolved impurities sty in this filtrate. Note: when you want the solid, use suction filtration. Clamp filtration flask and turn water aspirator used for?)on full. Wet filter paper with solvent used in recrystallization (water.) After filtration, break vacuum by taking the hose off filtering flask BEFORE turning off water. 6) Dry crystals until next week. When dry, weigh them and get melting point. W hat is mixed melting point? From the melting points, determine the identity of the unknown. Put the filtrate in the aqueous acidic waste container. % Recovery > (amount obtained after recrystallization / amount of crude) x 100 A recrystallization solvent should have the following properties: 1) Does not dissolve the compound to be purified when cold 2) Does dissolve the compound when hot (near boiling) 3) Has a low BP for easy evaporation from the purified compound 4) Does not react with the compound being purified 5) The cold solvent will keep the impurities dissolved Sample containing impurities have a broader and lower MP range than that of the MP range of the pure sample. If your compound has a MP higher than that of the literature value, it is not that compound. An impure compound melts lower than expected and has a larger than 2 degree range. You should use mixed MP to determine the compound’s identity. If you are confused which compound it is, mix the crystals of your unknown with the compound you think it may be. If they are the same, there will be no change in MP. If they are different, there will be a depression in MP since one compound acts as an impurity for the other. You cannot get a 100% percent recovery ever. A sample must be free of solvent (dry) before an accurate MP can be found MP may be used to determine the purit of an unknown based on its melting range or to determine the identity of the unknown given a source of known compounds. The MP of a solid is really a range . Heat at 12 degrees/min. It is best to take two MP of an unknown, the first along with a quick MP at 510 degrees/min. When you have an idea of the identity of your compound you should carry out a mixed MP: Mix some unknown with same amount of known. Determine MP. If they’re the same, there should be no change in MP. If they’re different, you will see a depressed MP with a broader range. Determination of Kd (Distribution Coefficient) Purpose: study the theory of extraction. Extraction: another term used for obtaining a substance from a mixture by mixing one liquid with another; the two liquids used must be immiscible. Liquid with more density will be on the bottom. Ether is less dense than water; organic solvent is more dense than water. After an organic reaction, extraction is often performed to isolate the desired product. Start with aqueous solution of benzoic acid of [known.] It is more soluble in organic solvents than in water. We will “extract” the benzoic acid FROM the (aq) solution INTO the organic solvent, and determine to which extent the benzoic acid was extracted (that extent is measured by its solubility in each of the solvents involved) by calculating the distribution coefficient for the extraction. The ratio of solubility is called the distribution coefficient; Kd=[ASx[ASo where [A]Sxs the [compound in extracting solvent], and [A] is the [substance in original solvent.] Sx is the So extracting phase, So is the original phase. Sx should be the solvent in which A is more soluble. The ratio of [ ] here is the same as the ratio of solubilities of the compound in the two solvents. The CH2Cl2 is the organic layer! Procedure: 1) Set up separatory funnel 2) Single Extraction: Label an “Organic Layer” flask and pour benzoic acid into the separatory funnel. Add dichloromethane (CH2Cl2) to funnel. Invert and shake and drain out the lower organic layer into the “Organic Layer” flask. Pour the aqueous top layer (CH2Cl2) out from the top of the funnel into a beaker. Determine the amount of benzoic acid in each layer by letting the CH2Cl2 evaporate over a week. Weigh your flask and benzoic acid in it next week and find the amount of acid extracted into the organic layer. Calculate the amount of acid left in (aq) layer. Find Kd. 3) Multiple Extraction: Pour benzoic acid into the separatory funnel. Add dichloromethane (CH2Cl2) to funnel. Invert and shake and drain out the lower organic layer into the “Organic Layer” flask. Add more CH2Cl2 to funnel, stopper and invert. Drain more organic layer out, and repeat a 3rd time. Now pour the aqueous top layer (CH2Cl2) out from the top of the funnel into a beaker. Determine the amount of benzoic acid in each layer by letting the CH2Cl2 evaporate over a week. Weigh your flask and benzoic acid in it next week and find the amount of acid extracted into the organic layer. Calculate the amount of acid left in (aq) layer. Find Kd. (You do THREE extractions with 10 mL CH2Cl2 each time, instead of doing 30 mL once.) Single Extraction Notes: Before extraction, # moles benzoic acid = M X V After extraction, # moles benzoic acid that were extracted into the CH2Cl2 is found by evaporating the CH2Cl2 and weighing the product, divide by molar mass of benzoic acid, and grams can be used instead of moles. # moles of benzoic acid left in the (aq) layer can be found by subtracting the moles of benzoic acid found in the CH2Cl2 layer from the total number of moles of benzoic acid in the start of the experiment. Kd = [acid in organic layer]/[acid in (aq) layer] Chemically Active Extraction Objective: Separation of an unknown tertiary mixture into components by extraction. The mixture is a 1:1:1 ratio of organic neutral component, organic acid, and organic base. Two AB reactions occur in the separatory funnel. Vent immediately after each mixing. Procedure: 1) Label three flasks: Organic Layer (CH2Cl2) which has the neutral component, RCO2Na, which has the sodium salt of the organic acid component, and RNH3Cl, which has the hydrochloride salt of the organic base component. Part 1: Separation 1) Put 3.3 grams of sample mixture in beaker, dissolve in CH2Cl2, pour into separatory funnel. 2) Using separatory funnel, extract the solution using (aq) NaOH. The CH2Cl2 will be on the bottom. Add NaOH to CH2Cl2 and stopper and invert. Drain CH2Cl2 (organic layer) into a flask labeled “Organic Layer.” Pour (aq) layer through top into the RCO2Na flask. 3) Put the CH2Cl2 back into the separatory funnel and extract the organic layer two more times with NaOH. 4) Return the (aq) layer to the separatory funnel to carry out back extraction. 5) Carry out one extraction with CH2Cl2 on the combined (aq) layers to ensure that any neutral compound is removed. This is back extraction. 6) Drain the lower CH2Cl2 layer and add to organic layer from above. Set aside the RCO2Na flask. 7) Return the combined CH2Cl2 layers to separatory funnel 8) Extract the CH2Cl2 solution with HCl(aq) 9) Add 6M HCl and CH2Cl2 to separatory funnel, stopper and invert, drain lower organic layer into “Organic Layer” flask, and pour (aq) layer through top into the RNH3Cl flask 10)Put the CH2Cl2 back into separatory funnel and extract the organic layer twice more using 6M HCl each time, don’t need water 11)Return the (Aq) later back to separatory funnel for back extraction 12)Carry out one extraction with CH2Cl2 on the (aq) layers to make sure that any neutral compound in the water layer will be completely removed. Drain the lower CH2Cl2 layer and add to organic layer from earlier. Set aside the flask with the organic base. 13)Combine all CH2Cl2 layers and add solid Na2SO4 and mix. Part 2: Isolation and Recrystallization of Neutral Compounds This is used to recover and purify the neutral component from the extraction 1) Filter solid sodium sulfate and evaporate the CH2Cl2 filtrate. Allow for evaporation over a week 2) Weigh after a week. Recrystallize the crude product from water by the same procedure in experiment 1 (Recrystallization.) Collect recrystallized produce by suction filtration, let dry, weigh, % recovery, get MP, determine identity. Part 3: Isolation and Recrystallization of Acidic Component 1) Place (aq) solution with RCO2Na in a beaker and cool in ice bath 2) Acidify the solution by adding 6M HCl and cool in ice bath and collect precipitated product on a Buchner funnel with suction. This is the acidic component, RCO2H. Wash collected solid with cold water. 3) Next week, weigh the crude organic acid compound. Recrystallize the acidic component with hot water and filter the hot solution using a prewarmed funnel and paper. Let filtrate cool and collect recrystallized product by suction filtration using a Buchner funnel, let dry, weigh, % recovery, get MP, determine identity of acidic component. (Aq) filtrate from recrystallization goes in acidic aq waste. Part 4: Isolation and Recrystallization of Basic Component 1) Put (aq) solution with RNH3Cl in beaker and cool in ice bath 2) Basify it by adding 6M NaOH. Collect precipitated product on a Buchner funnel with suction. This is the basic component. Wash collected solid with cold water. 3) Next week, weigh the crude organic base compound. Recrystallize the basic component with hot water and filter the hot solution using a prewarmed funnel and paper. Let filtrate cool and collect recrystallized product by suction filtration using a Buchner funnel, let dry, weigh, % recovery, get MP, determine identity of basic component. Aq filtrate from recrystallization goes in basic aq waste. Chromatography Purpose: to carry out TLC (thin layer chromatography) and CC (column chromatography) on a “reaction mixture.” TLC gives the analysis of a mixture, used for monitoring the progress of a reaction, analyzing a reaction mixture, or determining the solvent choice on the large scale column chromatographic separation. CC is a preparative tool; it gives the isolation of separate compounds. We use it to purify large amounts of substance for further use. Chromatography is generally a method of separation, a mixture is partitioned between a stationary phase (usually liquid/solid) and a moving/mobile phase (usually a gas/liquid.) As the mobile phase moves over the stationary phase, the mixture is equilibrated between the two phases according to the distribution coefficient. In TLC, the moving phase is an organic solvent called the eluent. The stationary phase is the adsorbent (ex.silica or alumina) Column chromatography is similar but done in a vertical column. Gas chromatography uses a gas vapor as the moving phase and a high BP liquid as the stationary phase. Separation occurs in chromatography because the organic compounds interact with the alumina or silica and partition between the adsorbent and the moving phase. The more polar functional groups of the compounds in the mixture are, the stronger the attachment to the silica or alumina. Constant EQ means that different compounds will move down the column or up the TLC plate at different rates depending on the affinity for the adsorbent versus the affinity for the solvent. Part A: TLC We spot a small amount of a substance as a dilute solution on a thin layer of adsorbent coated on a plate, then the plate is put in the TLC chamber (a jar) that has solvent (eluent) which travels up the thin layer. Colored spots will appear and the Rf value can be found (the distance a substance moves/distance of solvent front from point of application.) If the mixture is not colored and has no spots, put in an iodine chamber to form brown spots, or under UV light. A dark spot will come wherever an organic compound with conjugated bonds is located. Spotting of plates: Take some solution with a MICROpipette and touch the adsorbent from the bottom of the plate. Let solvent evaporate and spot again Development: Put filter paper in a beaker and this is the TLC chamber. Pour in solvent (eluent) to saturate the paper and put the plate in, cover with a glass or aluminum and let solvent rise up the plate and mark the solvent front with a pencil before it evaporates. Make sure there is enough solvent (eluent) present! Visualization:Let solvent evaporate and view plate. Or under UV light or iodine chamber. Do this in fume hood: 1) Solution of ferrocene and acetylferrocene from an acetalization reaction is used, both are orangeyellow colored. 2) Spot the mixture on 3 TLC plates and put in chamber with solvent in it. 3) Elute one plate with pure petroleum ether, one with a 9:1 V/V mixture of petroleum ether and diethyl ether, and last one with 1:1 mixture of petroleum ether and diethyl ether. 4) Remove the developed chromatogram and mark solvent front. Air dry plate and circle spots 5) Prepare a TLC plate with sample mix, a sample of ferrocene, and a sample of acetylferrocene, using appropriate eluent from above 6) Calculate Rf values for each spot on chromatogram What factors affect Rf values in TLC? Describe how solvent polarity affects Rf Part B: CC 1) Preparing the column: Weigh 8 g of acidic alumina 2) Put a plug of glass wool at the bottom of the column and fill it ⅓ full of petroleum ether 3) Add enough sand to form a layer over the wool and pour in alumina. Make sure the alumina does not adhere to the walls or wash it down with petroleum ether and Pasteur pipette 4) When alumina has settled, add sand to provide a protective layer at the top. Open stopcock, let solvent fall until it is above the upper layer of sand, and the column is ready to use now. 5) Taring = weighing, tare your Erlenmeyer flasks before use Chromatography of a mixture of ferrocene and acetylferrocene 6) Add acetylferrocene (toxic) and ferrocene mixture that has been dissolved in CH2Cl2 to the top of the column to not disturb the sand. Drain the solution to the sand and add petroleum ether to column. Drain below the sand, add more petroleum ether and drain below sand again. The mixture of compounds should be washed all the way through the sand layer and onto the column such that the addition of petroleum ether does NOT make a yellow solution. M ost important part. If the compounds are not below the level of the sand and a yellow solution appears, your results will be wrong. 7) Elute the first compound from the column using petroleum ether. The yellow orange bands moving down the column, collect this in a flask (only colored bands.) 8) Add 1:1 mix of petroleum ether and diethyl ether and elute the 2nd component which will be the same color band. Replace all bottle lids right away or ratio of the mixture will change because of evaporation of more volatile solvent. C ollect second colored fraction in a flask. 8) Spot a TLC plate with these 2 solutions. The purity of these fractions are assayed by the TLC; the plate is eluted with a 30:1 V/V mixture of tolulene and absolute ethanol. 9) Put the column fractions in the organic waste container. 10) To clean the CC, the column is emptied into a beaker. Remove stopcock, apply air pressure to tip. If the wool remains in the tube after the alumina leaves, wet it with acetone and reapply air pressure. Alumina is put into solid waste container, not trash or sink. Wool plug goes in trash or with alumina.
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'