Tag: dyes and pigments

If a homogeneous solution is observed in the direction of light, it appears clear and when it is observed from a direction at right angles to the direction of the light beam, it appears perfectly dark. 

Auxochromes are commonly called as color helpers or color intensifiers. Dyes containing auxochromes are basically aromatic compounds and include the presence of aryl rings which have delocalized electron systems. These are responsible for the absorption of different radiations with different wavelengths based on the energy of the electron. If an auxochrome is present in the meta position of the chromophore, then there is no change in the color. Electrons present in the chromophore get excited from the ground level to the excited state.

When visible light falls on them. Chromophores also alter the energy in
the delocalized systems. A chromophore gives the dye the property of absorbing different radiations whereas auxochrome imparts it with the property of being colored.
Hence option A is correct.

Vat dyes are essentially insoluble in water and incapable of dyeing fibers directly. However, reduction in alkaline liquor produces the water-soluble alkali metal salt of the dye, which, in this leuco form, has an affinity for the textile fiber. Subsequent oxidation reforms the original insoluble dye. The color of denim is due to indigo, the original vat dye.

Hence option A Is correct.

Auxochrome is a Greek word arising from; Auxo meaning to increase and chrome meaning color. An auxochrome is a group of atoms which will impart a particular color when attached to a chromophore but when present alone, will fail to produce that color.
Chromophore is that part of the molecule which when exposed to visible
light will absorb and reflect a certain color.
Hence option A is correct.

Auxochrome is a Greek word arising from two-word roots; Auxo meaning to
increase and chrome meaning color. An auxochrome is a group of atoms
which will impart a particular color when attached to a
chromophore but when present alone, will fail to produce that color.

A chromophore is that part of the molecule which when exposed to visible light will absorb and reflect a certain color. Auxochrome increases the color of any organic substance.
Hence option B is correct.

Auxochrome is a Greek word arising from two-word roots; Auxo meaning to
increase and chrome meaning color. An auxochrome is a group of atoms
which will impart a particular color when attached to a chromophore but when present alone, will fail to produce that color.

The chromophore is that part of the molecule which when exposed to visible
light will absorb and reflect a certain color.
Hence option A is correct.

Dispersed dyes were originally developed for the dyeing of Cellulose acetate and are water-insoluble. The dyes are finely ground in the presence of a dispersing agent and sold as a paste, or spray-dried and sold as a powder.
Hence option A is correct.

An auxochrome (Greek auxnein: "to increase" and chrma: "colour") is a group of atoms attached to a chromophore which modifies the ability of that chromophore to absorb light. They themselves fail to produce the colour; but when present along with the chromophores in an organic compound intensifies the colour of the chromogen.[1] Examples include the hydroxyl group (-OH), the amino group (-NH2), the aldehyde group (-CHO), and the methyl mercaptan group (-SMe).[2]

 An auxochrome is a functional group with nonbonded electrons when attached to the chromophore, changes both the wavelength and intensity of absorption. If these groups are in direct conjugation with the pi-electron system of the chromophore, they may increase the wavelength of light
that  is being absorbed and as a result,t intensify the absorption. A feature of these auxochromes is the presence of at least one lone pair of electrons which can be viewed as extending the conjugated system by resonance.

Hence option B is correct.

A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution and may require a mordant to improve the fastness of the dye on the fiber.
Hence option C is correct.

Basic dyes are water-soluble cationic dyes that are mainly applied to acrylic fibres but find some use for wool and silk. Usually acetic
acid is added to the dye bath to help the uptake of the dye onto the fiber.
Basic dyes are also used in the coloration of paper.
Hence option D is correct.