Write an Ib Lab Report

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Relevant IB topic: T3                                                                               Time: 2 hours


The principal chemical constituents of living matter are: water, mineral salts, organic compounds such as carbohydrates, proteins, lipids, nucleic acids. In this exercise we shall concentrate on carbohydrates, lipids, proteins, and we shall estimate the concentration of Vitamin C, an organic compound, in a solution, by the iodometric technique. • Carbohydrates include simple sugars, disaccharides and polysaccharides. They are the most important source of energy for most organisms. Polysaccharides change color in the presence of iodine solution: Glycogen gives a red-brown color and starch a dark blue–violet color. While simple sugars, having an aldehyde group, or a ketone group act as reducing agents in the presence of Benedict’s reagent producing a range of colors from green to brown depending on the degree of reduction they exhibit. In a solution of sufficiently high pH, sugars can reduce weak oxidizing agents such as cupric ions. Benedict’s solution contains sodium bicarbonate, sodium citrate and copper sulfate. If combined with a reducing sugar and heated, the divalent copper ion Cu of copper sulfate is reduced to the monovalent copper ion of cuprous oxide Cu2O which forms a precipitate ranging in color from green to brick red.              Glucose + CuSO4 + heat -------------- Cu2O + H2O + oxidized glucose  • Lipids such as fats and oils are important in cell membranes and also as an energy reserve. They produce translucent spots on paper. In addition they dissolve a non-polar Sudan III /IV dye, and produce cloudiness with alcohol.

• Proteins have a vital role in the growth and repair of tissues; also they have a role to play in cellular metabolism since most enzymes are proteins. The presence of two or more peptide bonds gives a violet color with Biuret’s reagent (NaOH & CuSO4).

• Vitamins are organic compounds required in small doses, most of them act as coenzymes. The iodometric technique has been developed for the estimation of Vitamin C conc. As iodine is added to the solution it combines rapidly with Ascorbic Acid to form the iodocompound according to the equation;                          C6 H8 O6 + I2    →    C6 H8 O6 I2  


Starch paste (cornstarch)                      4 test tubes Glucose solution                                   marking pen Sucrose solution                                   Iodine solution Glycogen solution                                 test tube rack Distilled water


• Fill 5 test tubes with 2 ml of the following: distilled water (tube 1), glucose solution (tube 2), sucrose solution (tube 3), starch solution (tube 4), and glycogen sol (tube 5).

• Add 3 drops of iodine solution to each of the above test tubes and swirl to mix.

• Record and analyze your observations.

Glucose solution                       dilute hydrochloric acid Galactose solution                    Benedict’s reagent Sucrose solution                       distilled water Starch suspension                     boiling water bath Test tube holders                      test tube rack                Marking pen                             6 test tubes  METHOD

• Mark 6 test tubes and fill each test tubes with 2ml of the following: distilled water (tube 1), glucose sol (tube 2), galactose sol (tube 3), starch sol (tube 4), sucrose sol (tube 5). Fill tube 6 with 2ml of sucrose sol and add few drops of hydrochloric acid.

• Add 2ml of Benedict’s reagent to each of the 6 test tubes.

• Place the test tubes either in a boiling water bath or in a beaker of boiling water and wait for few minutes.

• Record and analyze your observations.

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