Synthesizing Pigment and Dyeing Cloth

Teacher: Christine Smith
School: Hubbard High School
Suggested Grade Level: High School
Title: Indigo: Synthesizing Pigment and Dyeing Cloth
Subject: Chemistry
Time: 30 minutes

Index:
Background
Materials
Vocabulary
Objectives
Procedure
Safety Precautions
Assessment
State Goals and Chicago Academic Standards

Background
Indigo was originally a plant-derived blue dye, but it is now synthesized through chemical reactions. Generally, the chemical molecule is able to show color because of the pi bonds in its structure. In order to dye fabric, indigo must be made water-soluble by reducing it in a basic solution. At this point in the process, the dyed fabric appears yellow. When the fabric is exposed to air, it reacts with oxygen. The oxidized dye turns blue and is no longer water soluble, allowing the dye to stay affixed to the fabric.

Materials
Flinn Scientific Kit #AP9319 Vial Organic Indigo Dye Lab
Gloves

Vocabulary
Oxidation/reduction
Vat dyes
Soluble/insoluble
Double bonds/pi bonds
Indigo/leucoindigo

Objectives
1. Create a synthetic dye
2. Oxidize this dye and record the effects

Procedure
Have students
1. Combine o-Nitrobenzaldehyde with acetone in a base to make the indigo dye
2. Filter and dry the dye
3. Make the dye water soluble by reducing it with sodium dithionite in a strong base. It will become yellow.
4. Place fabric into dye and let soak for several minutes. Then remove from dye and let fabric air dry. The color will change to blue.

Safety Precautions
Never use an open flame — a hot plate works well. Acetone is flammable and a fire risk. This dye will stain so wear gloves and aprons. NaOH is very dangerous to the eye. As always, goggles must be worn. o-Nitrobenzaldehyde and acetone are moderately toxic by ingestion (and inhalation for acetone).

Assessment
Evaluate students on their manipulative skills and on their ability to recognize the reasons for the steps required to make dye usable.

State Goals and Chicago Academic Standards

Chemistry
State Goal 12/Chicago Academic Standard C
Chicago Framework Statement 1, 2, 4

Conceptual Statement—Chicago Program of Study
Chemical reactions occur when atoms, molecules, and ions interact. These interactions follow definite patterns of charge with measurable rates.

Supporting Ideas
The Law of Conservation of Matter and Energy is expressed in terms of balanced chemical equations (e.g. the mole concept, reaction categories, and oxidation-reduction).

Oxidation in characterized as the loss of electrons, whereas reduction is the gain of electrons.

The rate of a reaction is affected by changes in temperature, by the use of a catalyst, by changes in surface area, and by agitation.