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This 2 page Study Guide was uploaded by Giselle Foss on Wednesday May 4, 2016. The Study Guide belongs to CH 136 at University of Hartford taught by Dr. Sylvie Gauthier in Spring 2016. Since its upload, it has received 26 views.
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Date Created: 05/04/16
CARBOHYDRATES Name: Giselle Foss Date: April 19, 2016 Objective: To observe, classify, and characterize various types of carbohydrates using different reactions. Experimental: For Part A, 5 mL of phenylhydrazine was added to two test tubes. 10 glucose was added to one tube, and fructose solution was added into the other tube. Both test tubes were placed into a boiling water bath for 1 ½ hours. After this time period passed, the contents of the test tubes were left to cool to room temperature by immersing them in a beaker filled with cold tap water. An ice water bath was then created and the tubes were left to cool in it for an additional 5 minutes. Vacuum filtration was then used to collect the crystals within each tube. The crystals were rinsed 3 times with cold, deionized water and once with 95% ethanol. Once the crystals were dried, the melting point of each compound was found. The remaining portions of both osazones were transferred into a mortar and were ground together thoroughly. A third capillary tube was then filled with this mixture and the melting point was taken. For Part B, granular yeast was placed into a 50 mL beaker with 4 mL deionized water. The yeast was then mixed and divided equally into two test tubes. 10 mL of sucrose solution was added to one test tube and 10 mL of starch was added to the other tube. The two solutions were placed in a 250 mL beaker with hot tap water and the water temperature was monitored to stay at about 40°C. The yeast solutions created were saved and utilized in Part C. 3 mL of Benedict’s reagent was added into 7 test tubes. 10 drops of the appropriate solution was added to each labeled test tubes: glucose, fructose, lactose, sucrose, starch, the sucrose+yeast from Part B, and the starch+yeast from Part B. All 7 tubes were placed into a boiling water bath for 5 minutes, taken out to cool and the reactions were observed. Results and Discussion: For Part A, the melting points obtained were 214.4°C for glucose and 216.2°C for fructose. Based on these melting points, it can be concluded that glucose and fructose are identical compounds. This is because the melting points are extremely similar. The carbon below 2 on both glucose and fructose are identical because this enables them to become identical osazones as the phenylhydrazine reacts with both carbon1 and carbon2. For Part C, the results are as follows: glucose, fructose, and lactose all had a red precipitate on the top of the blue Benedict’s reagent making them all reducing sugars; sucrose and starch both remained blue with no precipitate and are nonreducing sugars; yeast + sucrose solution turned green, but had no precipitate making it reducing; and yeast + starch had no reaction making it nonreducing. Carbohydrates can undergo oxidation in the presence of Benedict’s reagent, which is seen by the formation of red copper (I) oxide. Ketones, however, are unable to undergo oxidation, but can be converted from ketoses to aldoses if there is an –OH group on the carbon adjacent to the carbonyl group. The sugars that were oxidized were glucose, fructose, and lactose. The red precipitate on all 3 of these show that they are Aldehydes. The only other solution that presented a color change was the yeast + sucrose. This mixture changed from its’ original blue to a murky green color. The sucrose on its own was not oxidized. The addition of yeast allowed the ketoses to become an aldoses by the addition of an –OH group enabling it to become a reducing sugar. In terms of the yeast + starch, the starch remained a nonreducing sugar even with the addition of yeast.
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