The Color of Chemistry Name: Pre-Lab Questions: 1. Which of the dyes used in this experiment are considered to be azo dyes? Why does Date: this name apply? 2. Redraw the structure of methyl orange (Fig. 2), and identify the groups in the dye that will bind to ionic and polar sites in the fabric. The purpose of this activity is to investigate the interaction of dyes with different fabrics. The dyes are methyl orange, m green, and crystal violet (direct dyes); congo red (a substantive dye); and alizarin (a mordant dye). See Figure 2 for the struc the dye molecules. The dyes will be tested on a multifiber test fabric that contains strips of six different fibers–wool, acryli ester, nylon, cotton, and acetate (Figure 3). Experiment Overvievw CH3 O3S N-N Methyl Orange N (CH3)2 о он Alizarin Malachite Green (X=H) Crystal Violet [X N(CH3)2l NH2 NH2 SO3 Nat Figure 2. Chemical Structures of Dye Molecules.
The Correct Answer and Explanation is :
1. Which of the dyes used in this experiment are considered to be azo dyes? Why does this name apply?
Among the dyes used in this experiment, methyl orange is an azo dye. The term “azo dye” refers to a class of synthetic organic compounds characterized by the presence of one or more azo groups (–N=N–) in their molecular structure. These azo groups consist of two nitrogen atoms connected by a double bond, linking two aryl or substituted aryl groups. The presence of the azo group imparts vivid colors to these compounds, making them widely used in the textile and food industries.
Methyl orange contains an azo group connecting two aromatic rings, one of which is substituted with a sulfonic acid group (–SO₃H) and a methyl group (–CH₃), while the other is substituted with a dimethylamino group (–N(CH₃)₂). This structure classifies it as an azo dye.
2. Redraw the structure of methyl orange (Fig. 2), and identify the groups in the dye that will bind to ionic and polar sites in the fabric.
Methyl orange has the following structure:
CH₃
|
N–N
|
SO₃H
|
C₆H₄–N(CH₃)₂In this structure, the groups that can interact with ionic and polar sites in the fabric are:
- Sulfonic Acid Group (–SO₃H): This group is highly polar and can form hydrogen bonds with polar sites on the fabric, such as hydroxyl groups in cellulose fibers like cotton.
- Dimethylamino Group (–N(CH₃)₂): This group is polar and can interact with polar sites on the fabric through dipole-dipole interactions.
These interactions facilitate the binding of methyl orange to the fabric, influencing the dyeing process and the resulting color intensity.
For a detailed explanation of the chemistry behind methyl orange synthesis, you might find the following video helpful: