Starch-Iodine Test for Carbohydrates

Detecting starch in food samples using iodine solution

Qualitative Analysis Beginner (Middle School) 30 min ~$5.00

Objective

Use the iodine test to identify starch in various food samples and understand the molecular basis of the blue-black color complex.

Background

The starch-iodine test is one of the most visually striking qualitative tests in chemistry. Iodine (I₂) forms a deep blue-black complex with amylose, the helical component of starch. The iodine molecules slip inside the amylose helix, creating a charge-transfer complex that absorbs light strongly. This test does not work with simple sugars (glucose, sucrose) or with amylopectin alone, making it specific for amylose-containing starch.

Safety Warnings

  • Iodine solution stains skin and clothing
  • Do not taste any samples after adding iodine
  • Handle knife carefully when cutting food samples

Required PPE

goggles lab_coat

Materials

  • Iodine solution (Lugol's) (10 mL)
    I₂/KI solution
  • Starch solution (1%) (10 mL)
    Positive control
  • Glucose solution (1%) (10 mL)
    Negative control
  • Food samples (Various)
    Potato, bread, rice, apple, etc.
  • Distilled water (50 mL)

Equipment

Spot plate or small dishes Dropper pipettes Knife for cutting food samples White paper background

Procedure

1

Place small amounts of each food sample and control solutions in separate wells of the spot plate.

5 min
2

Add 2–3 drops of Lugol's iodine solution to the starch solution (positive control). Observe the blue-black color.

3 min
3

Add 2–3 drops to the glucose solution (negative control). Observe that the color remains amber/brown.

3 min
4

Add 2–3 drops of iodine to each food sample. Record the color change observed.

10 min
5

Classify each sample as starch-positive (blue-black) or starch-negative (amber/brown). Record in a data table.

9 min

Expected Results

Potato, bread, and rice should test strongly positive (deep blue-black). Apple and pure sugar solutions should remain amber/brown. The intensity of the blue color correlates with starch content.

Cleanup

Dispose of iodine-treated samples in general waste. Rinse spot plates and pipettes with water.

Details

Category
Qualitative Analysis
Difficulty
Beginner (Middle School)
Duration
30 min
Est. Cost
$5.00
Steps
5
Materials
5

More Experiments

Anion Identification Tests 60 min Beilstein Test for Halogens 25 min Borax Bead Test for Metal Ions 45 min Cation Identification by Precipitation 90 min Chromatography of Plant Pigments 60 min Flame Emission Spectroscopy 60 min Hard Water Testing with Soap Solution 40 min pH Indicator Rainbow 45 min Unknown Substance Identification Challenge 75 min

Frequently Asked Questions

What is the objective of Starch-Iodine Test for Carbohydrates?
Use the iodine test to identify starch in various food samples and understand the molecular basis of the blue-black color complex.
How difficult is Starch-Iodine Test for Carbohydrates?
This experiment is rated as Beginner (Middle School). It takes approximately 30 minutes to complete.
What safety precautions are needed for Starch-Iodine Test for Carbohydrates?
Key safety precautions include: Iodine solution stains skin and clothing; Do not taste any samples after adding iodine; Handle knife carefully when cutting food samples.
What materials are needed for Starch-Iodine Test for Carbohydrates?
The main materials required are: Iodine solution (Lugol's), Starch solution (1%), Glucose solution (1%), Food samples, Distilled water.
What results should I expect from Starch-Iodine Test for Carbohydrates?
Potato, bread, and rice should test strongly positive (deep blue-black). Apple and pure sugar solutions should remain amber/brown. The intensity of the blue color correlates with starch content.