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The Iodine Test sor Starch Essay

The purpose of this experiment was to use Iodine, Benedict and Biuret to test the reaction of the following 12 samples: 1% glucose, 0. 3% glucose-1-phosphate, 1% maltose, honey, 1% sucrose, 1%lactose, 1% glycogen, 1% starch, protein, beer, distilled water and an unknown solution (test tube: 300). The iodine test for starch was to test how would starch reacted if we put iodine in it. The color of starch before the test was clear. The color of the iodine was brown. When you added iodine into starch, the result was the starch solution turned dark blue.

Starch had a positive result is because of the complex of iodine stuck inside the amylase coil which produced a characteristic purple – black color (Elservier Science Publishers, 1988). Also, starch was composed of polymers of glucose and long linear chains were amylase (Alberts Bray, Hopkin Johnson, Lewis Raff, Roberts Walter, 2009). The Benedict’s test for reducing sugars was used to determine the presence of reducing sugars. The color of the samples before was clear. The color of the Benedict was blue.

When you added Benedict into the samples and heated it up in the hot water bath for around 5 minutes. The aldehyde functional group was the reducing agent in reducing sugars and they all had a positive result was because of their ability to act as a reducing agent during the Benedict’s test. A reducing agent donated electrons during a redox reaction and was itself oxidized. Reducing sugars had either an aldehyde functional group or have ketone group – in an open chain form – which can be converted into aldehyde (Sur, B. K. , R. K.

Shukla, and V. S Agashe, 1972). The Biuret test for protein was used to determine the presence of peptide bonds in proteins. The color of samples before was clear. Both sodium hydroxide and copper sulfate were clear color as well. When you added sodium hydroxide and copper sulfate into the samples, protein would turn into purple. The structure of proteins was form by the peptide bond, which was found between the carboxyl and amino group of two adjacent amino acid residues (Alberts Bray, Hopkin Johnson, Lewis Raff, Roberts Walter, 2009).

When peptide bonds were presented in an alkaline solution, the copper (II) ions would form a coordinated with four nitrogen atoms involved in peptide bonds. Copper sulfate solution was a blue color, but when the copper (II) ions were coordinated with the nitrogen atoms of these peptide binds, the color of the solution changes from blue to violet. The color changed was dependent on the number of peptide binds in the solution, so the more protein, the more intense the changed would be (American Chemical Society, 2000).

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