Title: Using chemical Indicators

Introduction: Using four chemical indicators, it is possible to determine the nature of a macromolecule. The aim of this lab is to identify the color changes made by each indicator, and apply this knowledge to identify the nature of two unknown macromolecules.

Materials and Methods:

Steps

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Materials

1) Clean out four test tubes. Obtain the four indicators to use in this experiment. Also Obtain samples of known Macromolecules, and two unknown. / Indicators: Benedict’s reagent, Lugol’s iodine, Sudan IV, and Biuret reagent
Macromolecules: monosaccharides, polysaccharides, lipids, proteins, two unknowns.
Test Tubes(4)
2) Prepare the four test tubes by filling one with 1ml. of Benedict’s reagent and heating it, another with 1ml. of Lugol’s iodine, another with three drops of Sudan IV and 2ml. of distilled water, and the last with three drops of Biuret reagent. / Distilled Water
3) Put 1ml. of distilled water into each test tube, and observe and record the color of each test tube under Control Result.
4) Clean out the test tubes, and prepare them by repeating step two. This time, insert one ml. of the macromolecule that each indicator tests for to it's respective test tube: Monosaccharides for Bededict's reagent, Polysaccharides for Lugol's iodine, Lipids for Sudat IV, proteins for Biuret's reagent. Observe and record the color of each test tube under Known Result.
5) Clean out the test tubes, and prepare them by repeating step two. This last time, drop one ml. of unknown into each test tube. Observe and record the color of each test tube under Unknown Result.

Results:

Test

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Known Result

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Control Result

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Unknown Result

Benedict’s / White/Brown / Light Blue / A. Brown
B. Light Blue
Lugol’s / Purple / Brown/Gold / A. Brown/Gold
B. Purple
Sudan IV / Light Pink / Red / A. Light Pink
B. Light Pink
Biuret / Purple / Milky Light Blue / A. Purple
B. Light Blue

Conclusion: Through comparing the Unknown Results with the Known and Control Results, it was determined which materials were present in each unknown. This experiment shows that Unknown A contains monosaccharides, lipids, and proteins. Unknown B contains polysaccharides and lipids. Of these results, the Benedict's test may not be as accurate as possible, because it would not always turn to brown as experimental evidence says it should. This means that it is a possibility that the resulting color change could have been misinterpreted. This could be attributed to the age of the Benedict's reagent. Also, it is possible that since the unknowns had so many macromolecules in them, that some had settled to the bottom. This means that an unknown could have failed a test that it should have passed, because the only tested liquid was that which was drawn from the whole sample. A more accurate test would involve very fresh indicators and well mixed samples.