CD.6

Question 1

What is a chromophore?

Answer 1

The part of the molecule that is responsible for its colour.

Question 2

What are three types of functional groups that are important in a dye molecule?

Answer 2

1. Functional groups that modify the colour of the chromophore, i.e. by extending delocalisation or altering adsorption.
2. Functional groups that allow bonds with fibres.
3. Functional groups that alter the solubility of the dye.

Question 3

What are three ways dyes can be bonded onto fibres?

Answer 3

1. Ionic bonding
2. Covalent bonding
3. Intermolecular bonding

Question 4

Which type of dye will bond ionically with protein fibres?

Answer 4

Acid dyes.

Question 5

Which functional group is important in acid dyes that allow bonding with fibres?

Answer 5

SO3H sulfonic acid side group, which when dissolved in water becomes SO3- sulfonate group.

Question 6

What condition is required for acid dye to be applied to protein fibres?

Answer 6

Acidic condition.

Question 7

What group on protein fibres allows it to bond ionically with acid dyes?

Answer 7

In acidic conditions, protein fibres will have NH3+ side group, which can form ionic bonds with SO3- groups on the dye.

Question 8

What are some examples of fabric that contain protein fibres?

Answer 8

Animal products like nylon, wool, silk.

Question 9

What are two ways of attaching dyes to fabric using covalent bonds?

Answer 9

1. Mordanting.

2. Fibre reactive dyes.

Question 10

What is used in mordanting to attach dyes to fibres?

Answer 10

Metal ions are used. Groups on dye and fibre form dative covalent bonds to the metal ions, forming chelate complex ions.

Question 11

What is used in fibre reactive dyes to attach dyes to fibres?

Answer 11

Reactive groups, such as triazine derivative are added to the dye to form covalent bridges betweent the dye and fibre.

Question 12

What groups are required on the fibre for covalent bonding?

Answer 12

OH groups and NH2 groups, typically present in cotton and cellulose.

Question 13

What are two types of intermolecular bonds that can be used to attach dyes to fibres?

Answer 13

1. Hydrogen bonds

2. Instantaneous dipole - induced dipole bonds (id-id)

Question 14

Which types of fibre contain lots of OH hydroxyl groups?

Answer 14

Plant/cellulose based products like cotton, hemp, bamboo.

Question 15

What are two important functional groups in dyes that allow hydrogen bonding?

Answer 15

OH and NH2 groups.

Question 16

What are two important things about hydrogen bonding between dyes and cotton fibres that prevent water to break these bonds?

Answer 16

1. Dyes should be linear molecules. This way they can align closely with fibre and have stronger intermolecular bonds.
2. They should attach in several places so its harder to break all the bonds and remove the dye from the fibre.

Question 17

Which type of fibre bond to dyes using id-id bonds?

Answer 17

Polyesters.

Question 18

What kind of dyes are used for polyesters?

Answer 18

Disperse dyes.

Question 19

What is a feature of disperse dyes?

Answer 19

They have very few polar groups.

Question 20

Are disperse dyes soluble in water?

Answer 20

No, they are not soluble in water. So they are disperse in water when dyeing. This also prevents colour loss due to washing.