CHEM120L Study Guide - Quiz Guide: Carboy, Fume Hood, Liquid

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salmondog75

5 Jun 2016

School

University of Waterloo

Department

Chemistry

Course

CHEM120L

Professor

Sue Stathopulos

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Document Summary

Weigh clean and dry calorimeter; include the lid and magnetic stir bar. Record the exact mass of naoh used on your data sheet. This naoh is the ~1m naoh solution which will be used in part c. Read the temperature of the water in the calorimeter and record it on the data sheet. All temperature readings should be recorded to the nearest 10th of a degree (record all digits that are certain and one more uncertain digit) With the thermometer in place in the calorimeter, slide the lid of the calorimeter to the side and rapidly pour the naoh pellets into the calorimeter and close the lid. Record the temperature every 10 seconds (from the time of mixing) for one minute, then every minute for an additional 24 minutes (note: this will give you twenty-four minutes of data) Once part a has been completed, pour the naoh solution from calorimeter into the 1l poly bottle.

Related Questions

For the lab below, what is the separation scheme?

Elimination of 1-octanol.

Apparatus Assembly:

Set up a distillation apparatus.

Using a preweighed 50-mL round-bottom flask as the distilling flask, add 7.5 mL of 1-octanol and weigh it again to determine the exact amount added. Add 2.0 mL of 85% phosphoric acid and 30 drops of concentrated sulfuric acid. Add a magnetic stir bar.

Use a 25 mL round-bottom flask as the receiving flask. Be prepared to immerse it into an ice bath to ensure that no octene vapors will escape into the lab; however, do not add the ice until after the distillation is underway or you will have extra water in your product (from condensation). Even more effectively, you can ice your condenser circulator, but don't do that until after distillation commences either.

Dehydration:

Ensure that the water is flowing in your condenser and begin to heat the distilling flask on the appropriate insert of your heater/stirrer.

The heating should be regulated because ideal time of the distillation should be 30 minutes. Too fast of a distillation will cause an incomplete reaction and isolation of the starting material. The temperature registered by your thermometer will rise very slowly at first, but when the refluxing (soon to be distilling) vapors hit the thermometer, the temperature will rise quickly. It should stabilize as the first condensate begins to form in the distillation condenser; from that point to the end of the distillation, record the range of temperatures: this is your boiling-point range (although in this experiment, the broad distribution of products may cause a broad range of temperatures).

Ideally, you do not want to collect distillate until the temperature is at least 110Â°C (as the distillate, below this temperature, is mostly water); however, since you will have to remove water anyway, this is not critical. However, you don't want to collect product at temperatures much above the boiling point of the octenes since that will increase contamination of your product with unreacted 1-octanol and S_N1 ether byproduct.

Continue the distillation until no more liquid is collected or until tar begins to form; if tar begins to form, stop the distillation. Be sure to not distill the reactants completely, as you will be left with a thick residual tar that will be nearly impossible to remove from the flask.

Isolation and Drying of the Product:

Transfer the distillate to a separate container (flask or separatory funnel) with the aid of an approx. equal quantity of saturated sodium chloride solution (brine). Allow the layers to separate; remove the bottom aqueous layer (using a Pasteur pipet if you chose a flask) and discard it.

Transfer the organic layer (using a dry Pasteur pipet if you chose a flask) in the container to a small round-bottom flask and add a small amount of anhydrous sodium sulfate. Stopper the flask and allow it to sit for 10-15 minutes.

When the product is dry, transfer it to a pre-weighed screw-cap vial (preferably with a Teflon liner) and obtain its mass. Then filter a solution of dichloromethane and product into a GC vial, properly label it, and submit it to the GC vial collection box. The proper ratio of product in dichloromethane is 1 drop in 1-1.2 mL DCM: one drop in a full syringe of DCM.

For this experiment, you will also be required to set up the GC-MS to run your sample by adding your run to the instrument sequence. Follow the instructor's instructions with regard to this task.

Please answer the prelab questions only that are 1,2 and 3. Thankyou

Using models may be helpful in answering these questions. If the brominating of room -still bone proceeded by seen addition what isomer(s) of stolen bromide would be formed? If the brominating of trans-stolen proceeded by anti-addition what isomer(s) of stolen bromide would be formed? Which isomer(s) of stolen bromide would be formed if the reaction followed Mechanism 4? Bromine is very toxic and corrosive. It can cause severe chemical burns on skin contact. Bromine vapor is very harmful. Make all transfers of bromine in the hood and if any is spilled, contact the instructor at once. Carry out the brominating part of this experiment in a hood. There is room to allow 2-3 people to work at each hood. Add about 2 g of trans-stolen to a thoroughly dried 125-ml. Erlenmeyer flask containing a dry magnetic stir bar. Add 20 mL of methylene chloride to the flask and swirl until the solid has dissolved. Clamp your flask to a ring stand over a magnetic stirrer. Adjust the stirring rate so that it is vigorous but without splashing. Obtain about 6 mL of a 2 M bromine solution in methylene chloride (approximately 10% bromine by volume) in a test tube. (Your instructor will provide the prepared solution.) A graduated cylinder will be placed in the hood to let you measure the bromine solution, this will avoid taking bromine-contaminated glassware out of the hood or to your bench. Once you have obtained your bromine solution, place the test tube in a small Kroc mayor flask for support and take it to your set-up in the hood. Carefully add about 1/3 of your bromine solution to your flask and note what color changes occur. Once the characteristic red-brown color of bromine has faded, add another third of your bromine solution to the flask. Again, note what changes occur. After the color has faded, add the remaining bromine solution. This lime, the color of bromine should persist for 3-5 minutes and not fade. If the color persists, the reaction is completed, and the color is due to excess bromine in the solution. If the color still fades, the reaction is not quite complete. If this is the case, add 10 drops of bromine solution and continue stirring until the color persists. A considerable amount of precipitate (the crude product) should be visible by this time. It may be difficult to determine if you have an excess of bromine. Allowing the material to settle for a minute or two should help you determine whether there is excess bromine in the solvent. Once you have a solution containing a small amount of excess bromine, add 1-2 drops of cyclohexane. This should cause the bromine color to disappear quickly. If the color still persists, add cyclohexane one drop at a time until the color fades, taking care not to add too much. Once the bromine color is gone, suspend the flask in an ice bath for 10-15 minutes, then recover the product by vacuum filtration on the Buchner funnel. Rinse the flask and product with two 3-ml. portions of ice-cold methylene chloride. Allow air to pass through your solid for at least 10 minutes to give your product lime to dry. Remove the solid from the Buchner funnel, and allow it to air dry for 10 minutes. Obtain the mass of your isolated product and determine its melting point. The melting point of racemic stilbene dibromide is 112-113 degree C. The melting point of meso-stilbene dibromide is 241-243 degree C. Calculate the yield of your product. You may be asked to obtain an IR spectrum for your product. Submit your product in an appropriately labeled vial.

CHEM120L Study Guide - Quiz Guide: Carboy, Fume Hood, Liquid

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