Organic Compounds

Some simple tests for common substances suitable for secondary school classes.

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A. Carbohydrates

Simple Sugars

Benedict's Solution (alkaline solution of copper sulfate) will react when heated in the presence of simple sugars to form a red precipitate.

• Link to view of positive test with honey
• Link to negative test with sucrose

Starches

I2KI (Solution of elemental ioding and potassium iodide) will become opaque purple in the presence of starch

• Link to positive starch test in a corn grain

Testing the hypothesis, "Chlorophyll is necessary for Photosynthesis."

• Link to each step in processesing a Coleus leaf
• Link to view of live leaf and processed leaf stained with iodine

B. Lipids

Sudan IV: this stain is dissolved in alchohol. It has a greater affinity for nonpolar compounds than for polar compounds like water. It will diffuse into plant tissues containing lipids and color them light red.

• Link to photomicrograph of peanut tissue testing positive for starch
• Link to photomicrograph of peanut tissue testing positive for lipids

C. Proteins

Concentrated Nitric Acid: will react to phenolic "R" groups on amino acids to form a yellowish product. When followed by a treatment with ammonium hydroxide, will form an orangish color.

• Link to positive protein test in a corn grain

Enzyme Action:

• Link to view of experimental results. These samples were made from a beaker of startch after the addition of the enzyme diastase.

 

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