Identification of Organic Compounds

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Carlos Jarquin

April 17, 2009

BIO 35 - 8

Biology 35 – Identification of Proteins, Carbohydrates and Fats

Aim

To figure out the unknown solution based on the results of the Benedict’s reagent, Iodine solution, Biuret’s solution, translucency test and Sudan IV solution with the known solutions.

Problem

Can the results of the different tests to determine the presence of reducing sugars, starch, proteins and lipid on known solutions be used to classify and determine the unknown solution?

Hypothesis

Given that the unknown substance is the same as one of the known substance, the unknown substance should exert similar properties with each of the tests than its known counterpart solution. Therefore, by looking at the results, we will be able to compare the unknown solution to one of the known solutions and classify it.

Test for the Presence of Reducing Sugars (Benedict’s Test)

Background Information

Benedict’s reagent is used to determine the presence of simple sugars (monosaccharides and reducing sugars). Benedict’s reagent is a chemical compound made up of copper sulfate, which can detect the presence simple sugars. A reagent is a chemical that is applied to another substance in order to produce a chemical reaction that can give valuable information regarding the substance. In order to test solutions with the Benedict’s reagent, a small amount is added to the solution and then is boiled for several minutes to test the amount simple sugars present. The results will show precipitates within the tested substance.  The precipitates show the amount of simple sugars present. Since the precipitates are likely to be very small, Benedict’s reagent also shows the color changes that can gauge the amounts of the simple sugars. In the presence of simple sugars, the Benedict’s reagent changes color to green, yellow, and brick-red, depending on the amount of simple sugar. Reducing sugar is oxidised when heated with Benedict's solution, which means the sugar looses electrons. Benedict's solution contains copper sulphate. The copper 2+ ions in copper sulphate gain an electron that the sugar has lost and become copper 1+ ions - this is called reduction. The copper ions immediately react with oxygen to form copper oxide which forms a reddish brown precipitate. The redder the solution looks, the more copper oxide there is, and therefore the more sugar is in the solution.

Problem

Can the effect of the reaction of the Benedict’s reagent to test for the presence of simple sugars (monosaccharides and reducing sugars) with the known solutions be used to determine the unknown solution?

Hypothesis

Based on the background information, if the Benedict’s reagent causes the solution to turn green, yellow or brick-red, then we can conclude that there is a presence of simple sugars (reducing sugars); however, if there is another change in color than the ones presented above, there is no presence of simple sugars. Therefore, we can compare to the unknown solution in addition to its color change to determine which solution it is.

Materials

  • Solutions – Sucrose, Glucose, Fructose, Starch, Albumin, Gelatin, Skim Milk, Water, Water, Corn Oil, Unknown Solution (1 mL of each; equivalent to 10 eyedropper drops)
  • 150 mL Graduated Cylinder (± 0.005 mL)
  • 600 mL Beaker (± 0.005 mL)
  • Benedict’s Reagent (10 mL)
  • Test Tube Stand
  • Water (300 mL)
  • 10 Test Tubes
  • Eyedropper
  • Stopwatch
  • Hot plate

Variables

Independent (Manipulated) Variable

  • The different solutions to be combined with the Benedict’s reagent to determine the presence of simple sugars.

Dependent (Responding) Variable

  • The color change that occurs in each of the solutions after the Benedict’s solution is added.

        Controlled Variables

  • Amount of reagent added
  • Temperature of the hot water bath
  • Time that test tubes was in the hot water bath

Controlling of Variables

  • Independent (Manipulated) Variable: The independent variable was varied by using different known solutions with the Benedict’s reagent to create a variety of results.
  • Dependent (Responding) Variable: The dependent variable was monitored by recording the color change of the result between the reactions of the solutions with the Benedict’s reagent.
  • Controlled Variables: The amount of Benedict’s reagent added to the each of the solutions was controlled by limiting the amount added to 10 eyedropper drops (equivalent to 1 mL). The temperature of the hot water bath was controlled by setting the hot plate to 8 for each test tube. The time that the test tubes were in the hot water bath was controlled by using a stopwatch and each test tube was in the hot water bath for 3 minutes.

                

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Procedure

  1. Prepare a hot water bath using a 600 mL beaker half filled with water. Place on a hot plate and heat to boiling.
  2. Using the following steps, test each of the substances in a table for the presence of reducing sugars.
  1. Number clean test tube 1 – 10
  2. To each test tube, add 1 mL of substance to be tested
  3. To each test tube, add 1 mL of Benedict’s reagent
  4. Place the test tubes in the hot water bath for 3 – 4 minutes
  5. Record color.

Data Collection

The Color Change ...

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