Identifying Carbohydrates Essay Research Paper Lab Report

Identifying Carbohydrates Essay, Research Paper

Lab Report: #1 Identifying Carbohydrates


To determine whether a substance contains reducing sugars and/or polysaccharides (two types of carbohydrates) by using Benedict s reagent and iodine stain.


Carbohydrates are essential to living organisms, and the principal role of carbohydrates is the production of energy. Carbohydrates are groups of sugars that contain carbon, oxygen, and hydrogen in a 1:2:1 ratio. Three main units of carbohydrates are monosaccharides, disaccharides, and polysaccharides.

A monsaccharide contains one sugar unit, and has three to seven carbon atoms. Monosaccharides have a hydroxyl group bonded to each carbon atom; expect one, which is bonded to an oxygen atom thus forming a carbonyl group. If the carbonyl group is at the end of the chain then is it an aldehyde; therefore, if it is located in any other position it is a ketone. Common monosaccharides are ribose, deoxyribose, glucose, fructose, and galatose.

Two monosaccharides can be joined by dehydration synthesis to form a disaccharide. The hydroxide ions on carbon-1 of one molecule and the hydroxide ions on carbon-4 of another molecule give up two hydrogen atoms and one oxygen atom to form water, and then are joined together by the remaining oxygen atom. Common disaccharides are maltose, sucrose, and lactose.

Polysaccharides are the most abundant carbohydrate in the biosphere. Polysaccharides are long chains of monosaccharides, usually glucose, that are all hooked together by 1-4 glycosidic linkages formed through dehydration synthesis. There are two main categories of polysaccharides, storage polysaccharides and structural polysaccharides. Storage polysaccharides include starches and glycogen. The starches are bonded by carbon 1 of one glucose is linked to carbon 4 of the next glucose. Structural polysaccharides include cellulose. Cellulose is found in plant cell walls and is the most abundant organic compound on Earth.


The solutions that contain reducing sugars are the glucose/dextrose, table sugar, honey, sweet n low, and the equal solution; therefore, the potato, cornstarch, gelatin, and egg white solutions will contain polysaccharides. The water will contain neither reducing sugars nor polysaccharides.


The two tests indicate the present of reducing sugars and polysaccharides in the solutions being tested. The color change in table 1.4 refers to the concentration of reducing sugars in the Benedict s Reagent test and the types of polysaccharides present in the Iodine stain test. Benedict s Reagent when added to the solutions that contain reducing sugars will change the structure of the sugar; therefore causing the color to change. For the Benedict s Reagent test the colors are as follows: blue does not contains reducing sugars; bluish green, green, yellow, and orange red/rust test positive for reducing sugars, but at different levels of concentration. Iodine reacts with three-dimensional polysaccharides causing a change in the color corresponding to the polysaccharide type present. For the Iodine stain the test colors are as follows: yellowish amber does not contain polysaccharides; bluish black, dark reddish brown, and violet brown test positive for polysaccharides, but are different types of polysaccharide. The reason that some solution changed in color was due to the presents of reducing sugars or polysaccharides. The purpose of test one was to obtain a control group since water does not contain reducing sugars or polysaccharides. To determine whether the solution contained reducing sugars or polysaccharides the test tube needed to be held against a white background to obtain an accurate reading of the color. Then an observation of the solution determined whether the solution changed in color, which indicated the results of the two tests, performed.


The result of the Benedict s Reagent test showed that the glucose/dextrose and honey solutions contained high concentration levels of reducing sugars; the water and the table sugar solutions contained trace amounts of reducing sugars; the potato, cornstarch, sweet n low, equal, gelatin, and egg white solutions did not contained traceable amounts of reducing sugars.

The results of the Iodine stain determined that the potato and cornstarch solution contained polysaccharides. All of the other solution showed that polysaccharides were not present.


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