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Questions and Answers
What is the main purpose of after-treatments of direct dyes?
What is the main purpose of after-treatments of direct dyes?
- To decrease the molecular weight of the dye
- To increase the solubility of the dye
- To render the dye less soluble in water (correct)
- To enhance the light fastness of the dye
Why is it important for the preliminary deposition to be achieved with a soluble and comparatively small molecule?
Why is it important for the preliminary deposition to be achieved with a soluble and comparatively small molecule?
- To facilitate the in situ reaction (correct)
- To improve the color intensity of the dye
- To prevent the dye from entering the fiber
- To ensure easy removal of the dye
What group in the dye molecule allows it to be diazotized during the in situ reaction?
What group in the dye molecule allows it to be diazotized during the in situ reaction?
- Carboxylic group
- Primary amino group (correct)
- Sulfonyl group
- Phenolic group
In what year was the oldest method of improving fastness by an in situ reaction discovered?
In what year was the oldest method of improving fastness by an in situ reaction discovered?
Direct dyes exhibit good wet-fastness properties without any additional treatments.
Direct dyes exhibit good wet-fastness properties without any additional treatments.
The oldest method of improving fastness involved diazotizing the primary amino group attached to the aromatic nucleus.
The oldest method of improving fastness involved diazotizing the primary amino group attached to the aromatic nucleus.
What causes a complete alteration in shade when added to a dye molecule?
What causes a complete alteration in shade when added to a dye molecule?
After diazotization, the dye molecule is coupled with phenols or aromatic amines to form new azo dyes in situ on the fiber.
After diazotization, the dye molecule is coupled with phenols or aromatic amines to form new azo dyes in situ on the fiber.
The addition of another chromophore to the dye molecule during the in situ reaction does not affect the shade of the dye.
The addition of another chromophore to the dye molecule during the in situ reaction does not affect the shade of the dye.
If the dye molecule is too large, it will not enter the fiber, resulting in uneven dyeing.
If the dye molecule is too large, it will not enter the fiber, resulting in uneven dyeing.
The preliminary deposition of the dye should be achieved with a soluble and comparatively large molecule.
The preliminary deposition of the dye should be achieved with a soluble and comparatively large molecule.
The diazotization reaction is carried out in a hot solution containing sodium nitrite and excess hydrochloric acid.
The diazotization reaction is carried out in a hot solution containing sodium nitrite and excess hydrochloric acid.
The dye molecule Primuline, discovered by A.G. Green, exhibited good fastness to both light and washing before any after-treatments.
The dye molecule Primuline, discovered by A.G. Green, exhibited good fastness to both light and washing before any after-treatments.
The in situ reaction increases the molecular weight of the dye, rendering it less soluble in water and more fast to wet treatments.
The in situ reaction increases the molecular weight of the dye, rendering it less soluble in water and more fast to wet treatments.
$\text{The primary amino group in the Primuline dye molecule is represented by the structure } -NH_2$.
$\text{The primary amino group in the Primuline dye molecule is represented by the structure } -NH_2$.
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