Identification Of Carbohydrates 5a455k

Identification of Carbohydrates Carbohydrates consist of simple sugars (e.g. glucose, fructose and sucrose) and complex carbohydrates (large molecules called polymers made of hundreds of simple sugars). There are a large number of carbohydrates in living organisms, varying from small sugar molecules such as the simple sugar glucose, which provides all cells with the fuel needed to do cell work, to polymers such as cellulose (structural molecules of plants) and glycogen (a storage carbohydrate in animals). Because there are so many different types of carbohydrates, one chemical test cannot identify all of them. Different chemical reagents, or testing agents, are used to test for simple sugars and carbohydrate polymers. A reducing sugar is a type of sugar that can cause a specific chemical reaction, called a reduction. A reduction is a very common type of chemical reaction where a substance "gains an electron". Reducing sugars can cause certain types of molecules to get reduced (gain an electron). Not all sugars have the chemical structure to be reducing sugars. A reduction is always coupled to a chemical reaction called an oxidation, where a substance loses an electron. Reducing sugars lose electrons when they cause a reduction of some other chemical. Oxidation-reduction, or Redox, reactions are very important in the energy transfer chemical reactions of living organisms. A Benedict ? s test can be used to identify reducing sugars. The Benedict ? s solution (a chemical reagent) contains a blue soluble form of copper ions (Cu++) that can undergo a reduction (that is the copper ions gain electrons) when heated in the presence of a reducing sugar. When the blue copper ions are reduced, they change from the soluble blue color to reddish color copper ions (Cu+) that are insoluble. The color of the test solution changes from blue ---> green ---> orange ---> red-brown or rust color as more reduced copper ions are formed. You will use the Benedict's solution to test for the presence of reducing sugar in various substances.

Identification Of Lipids There are many different types of lipids. Among these are triglycerides (fats and oils), the major fuel storage molecules of most animals. Many lipid tests involve the use of fat-soluble dyes, such as Sudan dyes, which will be absorbed selectively by lipid molecules, and are visible when viewed through a microscope. For those who lack experience with detecting Sudan-stained oil globules, there is a much simpler lipid test, one which each of us has done many times while consuming our favorite junk food treats. In this exercise this test will be done as an experiment, complete with control. Unglazed paper such as a grocery bag or a napkin is normally opaque (light scattering). When lipids are placed on unglazed paper they will leave a permanent translucent spot through

which light can . Other substances may temporarily coat the paper, but only lipids will leave the paper permanently translucent. Identification of Protein Proteins are an important group of large molecules found in all living cells. Special proteins called enzymes mediate the chemical reactions necessary to maintain life. Transport proteins in the cell membrane control the age of various materials into and out of the cell. Proteins are polymers composed of amino acid subunits. The bonds that amino acids together in a protein are called peptide bonds. Biuret reagent detects peptide bonds and can be used to identify proteins. Chemicals of the Biuret reagent are NaOH and CuSO4 Biuret reagent is light blue, but in the presence of proteins it turns violet. Other types of molecules may cause other color changes, but only the violet color indicates proteins. Please note that sodium hydroxide (NaOH), a very caustic substance. Be very careful not to spill any sodium hydroxide. If you do get some on your hands, rinse them under cold water until they no longer feel soapy.

Conclusion In this lab you are going to perform some exercises that can be used to identify some specific types of chemicals commonly found in foods. Since each of the major groups of compounds has unique chemical and physical properties, they can be identified them by a chemical reaction that is distinctive for these properties. While performing these exercises you will also be learning the basic concepts involved in the experimental method. One of the more important parts of this is the use of a control. The control is an extra experiment or set of experiments against which all other experimental samples are compared in order to determine exactly what is causing a change. You will use a control in the following exercises. Be aware of what the control is and what it tells you.