CHEM 1201 : Test 1 Practice Exam (with Answers)

25 views13 pages

azuremammoth471

15 Mar 2019

School

Department

Course

Professor

For unlimited access to Study Guides, a Grade+ subscription is required.

Document Summary

The basic idea to understand is that the heat used by the reaction comes from the solution. qrxn qsolution. These heats are opposite in sign because heat flows from the solution into the reaction. After that some of the liquid water freezes. 00 g/ml x g nh4no3 10: 1 g ice, 02 g/mol. Notice also the enthalpy for freezing is negative. (energy is released for the phase transition s) So the work can be found from the equation w e q. Remember that both h and e depend on the amount of material present and this is the unknown value we are trying to find. 1 mole zn s x g zn s : 37 g/mol. Solving for x, the unknown mass of zinc gives mass 22. Solving for q we find q 16. Work is negative because the energy of work is leaving the system as the work is performed on the surroundings.

Related Questions

Question: For the following two experiments I have been asked to find at least 1 procedural change for each that could be made to improve the yield of my product. Please review the experiments and aid me in determining what this change might be. Thanks in advance!

Reduction of Benzophenone

1. In a 50 mL Erlenmeyer flask, dissolve 2.0 g benzophenone in 10 mL of methanol. Also add a stirbar to magnetically stir the solution.

2. Place your solution in an ice bath until the temperature has dropped to 10 C.

3. While your flask is in the ice bath, add 0.42 g of sodium borohydride, in small portions, over a 5 min period. The addition of sodium borohydride is exothermic, so you must take care to add it slowly to keep the temperature under control. This means adding the hydride in 5-6 portions, with about 1 min in between additions.

4. Once the addition of NaBH4 is complete and the vigorous bubbling has ceased, allow the solution to stir at room temperature for 10 minutes.

5. Carefully clamp the Erlenmeyer flask into a 80Â°C water bath and allow it to sit in the hot water bath for 2 minutes.

6. Remove the solution from the hot water bath and allow it to cool to room temperature and then cool it in an ice bath.

7. SLOWLY add 30 mL of cold water and then SLOWLY(dropwise) add 1.4 mL of 6M HCl. Use litmus paper to confirm that your solution is acidic. If your solution is not acidic, add more HCl until it is acidic. You should see the formation of a white precipitate at this point.

8. After adding the HCl, remove your solution from the ice bath and let it stir at room temperature for 20 minutes.

9. Collect the product by suction filtration, washing with 10-25 mL of cold water.

10. Allow the product to completely dry under suction and then record the crude weight.

11. Analyze the purity of your crude product by running a TLC. Dissolve a very small sample of your crude product and the benzophenone starting material in diethyl ether. Spot these samples on two separate lanes of your TLC place and develop the TLC pate with 9:1 petroleum ether: ethyl acetate.

12. If you are convinced that your crude sample is pure diphenylmethanol, record the final mass and run a melting point.

13. If you think some impurities are still present in your crude mixture, recrystallize your product with a minimal amount of hot hexanes. Review your notes from earlier in the semester if you donât remember the steps to run a recrystallization.

14. Record the mass and melting point of your purified diphenylmethanol and place it in a labeled vial to turn in to your instructor.

Oxidation of Diphenylmethanol

1. Place approximately 300-mL of hot (from the tap) water in a 400-mL beaker, add a boiling stone, and place it on a hot plate. Heat the water until it is 90-95 oC. It is important to keep the temperature just below 100 oC; thermal decomposition of the permanganate may occur at higher temperatures resulting in the release of toxic fumes.

2. While your water bath is heating, place 4.82 mmol of diphenylmethanol in a 10- or 25- mL round-bottomed flask.

3. Weigh out approximately 4 grams of the oxidant mixture of KMnO4/CuSO4â¢5H2O.

4. If the temperature of your water bath has reached 90-95 oC, combine the oxidant with the diphenylmethanol in your round-bottomed flask.

5. Vigorously stir the mixture with a microspatula for 5-10 min until the flask is warm to the touch. A color change from purple-blue to brown/black should be observed as you are stirring the solids. This is an indication that a reaction is occurring.

6. When the flask is warm, equip the reaction vessel with an air condenser and clamp it in the hot water bath. Be sure that the solid reaction mixture is below the surface of the water.

7. Heat the reaction for 1 h. Continue to monitor the temperature of the water; if the temperature increases close to 100 deg C, add a bit of cold water to keep the temperature 90-95 deg C and lower the heat setting on your hot plate.

8. After 1 h of heating, remove the flask from the hot water and allow it to cool to room temperature. Remove the reflux condenser.

9. Add 10 mL of hexanes to the solid and stir to mix. Remove the hexanes with a pipette and place it into a 25-mL Erlenmeyer flask. Repeat and combine the extracts.

10. Dry the combined hexane extracts with Na2SO4; decant/filter the hexanes into a preweighed 25-mL Erlenmeyer flask; and evaporate the hexanes using a gentle stream of air.

11. Analyze the purity of your crude product by running a TLC. Make samples of the following for TLC: stock benzophenone, crude benzophenone, and benzhydrol. Spot these samples on three separate lanes of your TLC place and develop the TLC pate with 5:1 hexane/ethyl acetate.

12. If you are convinced that your crude sample is pure benzophenone, record the final mass and run a melting point.

13. If you think some impurities are still present in your crude mixture OR if your product is not a solid, recrystallize your product with a minimal amount of hot methanol or methanol/water. Review your notes from earlier in the semester if you donât remember the steps to run a recrystallization.

14. Record the mass and melting point of your purified benzophenone and place it in a labeled vial to turn in to your instructor.

I want another 600 word discussion on 3-methyl-3-pentanol, here is the attached example if you need an idea. I don't want it to be the same.

"Discussion:

In this experiment, the 3-methyl-3-pentanol solution was being used in the dehydration process. The alcohol was a five carbons aliphatic hydrocarbon which one of the hydrogen atoms, H was substituted by one hydroxyl group, OH^-. Due to the low melting point, the pentanol appear in liquid form at room temperature. The dehydration process of alcohol converted pentanol which the hydroxyl group, OH^-was removed to become pentene. Pantene was a five carbons aliphatic hydrocarbon with a single double bond in the molecule. The solution was added with concentrated phosphoric acid in a 5-ml vial and was mixed together by swirling. The phosphoric acid was added as catalyze as such increased the rate of reaction in dehydration without affected the particular chemical reaction. The spin vain added into the solution in order to prevent over boiling of the solution.

The heating of mixture was carried out in a fractional distillation apparatus. As the mixture was heated, the alkene and water were produced as the products in the reaction. Besides, the side product and impurities of the reaction was being produced at the same time. The temperature of mixture when heating was fluctuated. During the temperature 80Â°C, the temperature of mixture dropped suddenly by 2Â°C and the temperature remained at 78Â°C constantly for few seconds. This was because some impurities or side products were being produced in the mixture which might had the boiling point of 78Â°C. The temperature of mixture dropped suddenly because the heat being was absorbed which used to break down the bonding of the side products. When the boiling point was reached, then temperature of mixture remained constant as the state of the side products are converted from liquid form to gaseous form. The temperature of mixture was increased until 107Â°C after all the side products were being converted.The temperature of mixture was reached to maximum at 107Â°C. This temperature was known as the activation temperature which the pentanol started to be dehydrated. In all the distillation process, some of the product was being lost since it washoled up in the apparatus which reduce the product yield. In order to maximize the yield, the mixture was continued to be heated at higher temperature range which more than the boiling point of pentanol. When the mixture was heated at 90Â°C-100Â°C, the water in the mixture pushed over the products into the receiving vial along the condenser. The products produced were collected in the same receiving vial.

Then, the receiving vial containing pentene, water and small amount of the impurities. Two layers liquid were presented in the receiving vial, one drop of distilled water was added into vial in order to determine the location of aqueous layer. Since the water droplet mixed with the lower layer, so the upper layer was determined as cloudy solution while the lower layer was aqueous layer. The upper cloudy layer was pentene with some impurities and water inside. The lower aqueous layer was removed and discarded. But, that is not easy to remove all the water in the receiving vial. So, anhydrous calcium chloride was being added. The purpose of adding of anhydrous calcium chloride was used to remove residual water in the organic solvent. It is known as drying agent in the organic solvent which are not dissolves in the solvent but drying the solvent. The calcium chloride clumped together with the water droplets as it solidified them. In another word, it reacted with water to form hydrates which was their preferred form when water was available. An excess drying agent should be used to ensure that all the water in solvent was removed. If the water remains in the materials collected, it could interfere with the analysis.Water had been successfully removed from the organic compound mixture, so it was very important to not reintroduce water into the mixture. The final distillation of unpurified 3-methyl-3-pentene must be done very carefully to obtain purified products. "

Please answer to the best of your ability