Write an Ib Lab Report

THE CHEMICAL CONSTITUENTS OF LIVING MATTER
Relevant IB topic: T3 Time: 2 hours

BACKGROUND

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

TEST FOR CARBOHYDRATES A. IODINE TEST
MATERIAL REQUIRED

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

METHOD

• 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. B. BENEDICT’S TEST
MATERIAL REQUIRED

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.

TEST FOR LIPIDS

A. SPOT TEST
MATERIAL REQUIRED

Brown wrapping paper Whole milk
Corn oil Skimmed milk
Distilled water Medicine droppers
METHOD
• With a medicine dropper add a drop of corn oil, of water, of whole milk, and of skimmed milk on different locations of a sheet of brown wrapping paper. You can mark the different sites beforehand.

• Let the paper dry, and then examine each spot by holding the paper up to the light.

• Record and analyze your observations.

B. SUDAN III/IV TEST
MATERIAL REQUIRED

Distilled water Whole milk
Corn oil Skimmed milk
Sudan III / IV dye 4 test tubes
Test tube rack marking pen METHOD • Fill 4 test tubes with 2 ml of the following: distilled water (tube 1), corn oil (tube 2), whole milk (tube 3), skimmed milk (tube 4).

• Add to each of the 4 test tubes few grains of the Sudan III/ IV dye.

• Record and analyze your observations C. ALCOHOL TEST
MATERIAL REQUIRED

Distilled water
Corn oil
Absolute alcohol
Test tube rack METHOD • Add 1 cm3 of corn oil to a 5 ml alcohol in a test tube and shake to dissolve. Add about 10 ml of distilled water and note any cloudiness.

• Record and analyze your observations.

TEST FOR PROTEINS

*BIURET TEST
MATERIAL REQUIRED

Albumin solution 3 test tubes
10% Sodium hydroxide test tube rack
0.5% Copper sulfate marking pen
Distilled water
Whole milk
*(Biuret’s reagent consists of sodium hydroxide & copper sulfate) METHOD • Fill 3 test tubes with 2 ml of the following: distilled water (tube 1), albumin solution (tube 2), whole milk (tube 3).

• Add an equal volume of 10% NaOH solution.

• Add 0.5% CuSO4 drop by drop and watch for a change in color, then stop adding.

• Record and analyze your observations.
TEST FOR VITAMINS[pic]

MATERIAL REQUIRED

1 ml pipettes 0.05% Vitamin C solution test tubes 2% Starch suspension
0.01M iodine solution teat pipettes METHOD • Use a pipette to measure 1.0ml of vitamin C solution obtained by crushing 2x250 mg tablets in 1L distilled water.

• Using a teat pipette add 6 drops of starch solution to the vitamin solution.

• Using another clean teat pipette, carefully add the iodine solution 1 drop at a time, mixing after each drop until the natural color of the solution is replaced by a blue black color.

• Record the number of drops.

• Repeat steps 1 and 2 three times and record your results.

• Knowing the relative mass of Ascorbic acid (176), using the solutions and technique suggested, and assuming 15 drops of I2 per mL, you can calculate the approximate concentration of Ascorbic acid (mg/L) in solution by multiplying the number of drops of iodine taken by 120.
In this investigation you will be assessed on: Data collection, Data analysis, Manipulative skills.