Organic Solutions and Reagents for Specific Organics

Purpose:  The purpose of this investigation is to acquaint the student with the categories of biologically important organics and with the reagents used to determine the type of organic.  The categories of organics that will be studied in lab are the following:

A fourth category, the nucleic acids, will not be considered in this lab exercise.

Materials and Methods:  For this exercise, the student will require test tubes, test tube rack, wax pencil, graduate cylinder, petri dish, pencil, filter paper, forceps, hot water bath, and several 150 ml beakers, knife, and mortar and pestle.

The reagents needed are dropper bottles of Benedict's solution, Iodine solution, Biuret reagent, and Sudan III.

The organics to be tested are dropper bottles of glucose solution, apple juice, starch-water preparation, potato juice,  egg albumin-water preparation, cottonseed oil, and a thin slice of coconut tissue.

Experiment:  Test these organics in the following manner:

Benedict's solution:  test for reducing sugars
Add about 5ml of glucose solution into a test tube.
Add about 5ml of apple juice into another test tube.
Now add about a full dropper of Benedict's solution into each test tube.  Allow the test tubes to stand in a warm water bath for about 15 minutes.  After this time, note the color change in each.

Iodine solution:  test for starch
Add about 5ml of starch-water preparation into a test tube.
Add about 5ml of potato juice (crush potato slices with the mortor and pestle) into another test tube.  Add one or two drops of iodine solution to each test tube and note the immediate color change.

Biuret reagent:  test for protein
Add about 5ml of egg albumin-water prepartion into a test tube.  Now add about a full dropper of Biuret reagent into the test tube.  Shake the test tube slightly and note the color change.

Sudan:  test for lipids
Obtain a round piece of filter paper.  With a pencil, draw a small circle on opposite sides of the paper.  Add a small drop of cottonseed oil to one circle and rub a bit of coconut tissue/meat in the other circle.  Lower the filter paper into a petri dish containing Sudan and allow the paper to soak for about 2 or 3 minutes.  Using forceps remove the filter paper and rinse with a slow stream of water at the sink.  Note the color change on the filter paper.

Conclusion:  Reagents are specific for particular organics.  If a reagent is added to a solution containing that organic, a color will develop.  A particular color represents a positive test for the organic.   Based on your tests identify these colors in the table below:

  organic solution                       reagent                            positive color

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