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13 Dec 2019

I weighed out 5 grams of powdered non-fat dry milk. Once I completed my isolation of casein. The dried casein weighed 1.55 grams. Please help me calculate the total yield of casein from the powdered milk.

5 grams of powdered milk should produce 0.2 grams of casein. Determine theoretical yield for exact weight of the milk and percent yield.

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Bunny GreenfelderLv2

16 Dec 2019

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When solutions containing 1.0000 g of BaCl2 and 1.0000 g of Na2SO4 were mixed, solid BaSO4 formed. The BaSO4 precipitate was filtered out of the solution, allowed to dry, and then weighed. The mass of BaSO4 that was isolated from solution was 1.0400 g. Use this information to answer the following questions. Pay close attention to the proper use and reporting of significant figures and units. You must show all of your work (i.e., your calculations) for full credit.

(a) Write a balanced chemical equation that shows the reaction that occurs when an aqueous solution of BaCl2 reacts with an aqueous solution of Na2SO4 to form aqueous sodium chloride and solid BaSO4. In your equation, you should indicate the physical states of each reactant and product. Note: Precipitation reactions are discussed in Section 4.6 of your textbook.

(b) Calculate the moles of BaCl2 that are available for reaction.

(d) Calculate the moles of Na2SO4 that are available for reaction.

(e) Calculate the grams of BaSO4 that should form if all of the available Na2SO4 reacts.

(f) Which reactant (BaCl2 or Na2SO4) is the limiting reagent in this reaction? Why?

(g) What is the theoretical yield of BaSO4?

(h) What is the percent yield of BaSO4? (See Section 4.3 of your textbook for information regarding the calculation of a percent yield.)

(i) If this reaction went to completion, then how many grams of the excess reagent should remain after the reaction is complete?

Need isolated yield in moles, theoretical yield in moles and grams, and percent yield!

synthesis of Dulcin, 4-Ethoxyphenylurea

1. In a 50 mL round-bottomed flask, place 1.4 mL (1.4 g, 0.01 mole) of p-phenetidine, 2.4 g (0.04 mole) of urea, and 5 mL of distilled water.

2. To this mixture, add 1 mL of concentrated HCl and 5-6 drops of glacial acetic acid.

3. Fit the round-bottomed with a reflux condenser, add a boiling stone, swirl the material well and boil the mixture vigorously until the reaction is complete (30 min. maximum). At first, the dark colored solution remains clear, but in 15-20 minutes the product begins to separate rapidly. When the mixture sets to a semi-solid crystalline mass, stop the heating immediately.

4. After cooling the round-bottomed flask to room temperature, add 3-4 mL of cold water, stopper the flask tightly and shake it thoroughly to make a slurry of crystals.

5. Collect the product by vacuum filtration, wash it with cold water and dry the crystals by drawing air through them while they are still in the Hirsch funnel.

6. Recrystallize the crude product from boiling water (30 mL/g of product) using decolorizing charcoal to remove the brown color, as follows:

a. In a small beaker (100 mL) bring to a gentle boil the crude dulcin in the appropriate amount of water (donât forget the boiling chip).

b. Add a small amount of decolorizing charcoal over the boiling liquid and keep boiling for 1 minute.

c. If the liquid (not the dark, floating particulates) is colorless, filter the hot mixture through a pleated paper filter, placed in a stem less glass funnel, into another beaker. If the liquid is still pink, repeat step b.

7. Chill the filtrate in an ice bath before vacuum-filtering the purified crystals. Dry the product, weigh it, determine a melting point.

For step 5 the product was weighed and turned out to be .32 g then after finishing the lab with step 7 the final product weighed in at .07 g

Isolated Yield _____ moles _____ grams

Theoretical Yield _____ moles _____ grams

Percent Yield ______ %

This is the description from my organic chemistry lab.

Lab Observations and Data

We obtained 1.17g of cyclohexene oxide (clear liquid) and 3 mL of water into a 50 mL flask with a stir bar. When added a single drop of sulfuric acid, the clear liquid started to change to a very, very light yellow/brownish color. We obtained an ice bath on the side in case our mixture started to boil. After the solution stirred for about 25 minutes, we added sodium hydroxide. We inserted a pH paper and it turned a dark blue, meaning basic. Added another drop of sulfuric acid to make it a little less basic. Added the mixture to a separation funnel, shook it around and ended with separated layers. We separated the layers, thinking the bottom layer was the organic layer, when it was really the aqueous layer. So we ended up mixing the wrong layers back together. After some error, we isolated our new organic layer and added some drying agent. We then put that mixture with the drying agent, NaOH, into the rotovap. Our final product was a white powder and weighed 1.51 grams. We then set up a vacuum filtration while boiling water. We boiled our dried organic layer into the hexane. Added two drops of ethyl acetate to help the boiling process go faster. After vacuum filtering it, it weighed .394 grams. The melting point is 91 to 93 degrees Celsius. Our IR spectra matches the "trans" conformation. So for our TLC plate we observed blue dots to match the trans conformation.

The question is "calculate your percent yield" Which is actual yield/theoretical yield x 100. I just dont understand how I get those numbers.

Here is the lab manual description as well.

Procedure for the Preparation of 1,2-Cyclohexanediol Place a mixture of 1.18 g (0.012 mole) of cyclohexene oxide and 3 mL water into a 50 mL Erlenmeyer flask, equipped with a magnetic stir bar. To this mixture with vigorous stirring add one drop of 6 M sulfuric acid (33% H2SO4) Caution: After a short incubation time, the reaction mixture will become quite warm. This epoxide ring opening reaction is very exothermic. (Why?) If the reaction mixture begins to boil, place the flask in a bath of ice and water. Allow the reaction mixture to stir for the next 15 minutes and let it cool to room temperature. Afterwards, add a small amount of 10% sodium hydroxide drop-wise to neutralize the stirring solution. (No more than 3 or 4 drops of 10% NaOH should be necessary.) Place a drop of the reaction mixture on pH paper to check the pH. Extract the product from the reaction mixture into ethyl acetate or diethyl ether (2 x 15 mL). Dry the combined extracts over sodium sulfate. Decant the solution and remove the solvent to yield the crude product (~1 g). The product can be purified by recrystallization from a small amount (~ 5 mL) of hot toluene or hexanes. Collection of the purified product by suction filtration yields 1,2-cyclohexanediol. The cis isomer has a melting point of 97-101 Â°C whereas the trans isomer melts at 101-103 Â°C. Determine the product(s) or products the reaction. Include a percent yield calculation in your report along with the results of your TLC analysis

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