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OCR B A Level Chemistry > Colour by Design > Flashcards

Flashcards in Colour by Design Deck (23)
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How do dyes attach themselves to fibres?

By intermolecular bonds, ionic bonds, or by covalent bonding


Why do good dyes need to be colourfast?

So they don't wash out too quickly or fade in light


What does colourfastness depend on?

The strength of the bond between the dye and the fibre.


If there's a -NH2 group in a dye, how will it bond to fabrics?

The -NH2 group allows H-bonding to take place with fibre. This type of bonding works particularly well with cellulose fibres because there's lots of -OH groups


Are dyes that use H-bonding colourfast?

Not particularly because H-bonds aren't that strong


How do dyes with acidic groups bond to fibres?

If there's an -NH2 group in the fibre, H+ ions from the dye move to the -NH group to make -(NH3)+. This allows ionic interactions to take place


What are the two strategies attaching dyes to fibres by covalent bonds?

Mordanting or adding fibre-reactive groups to the dye


Describe mordanting

This makes use of a metal ion to join the dye to the fabric: groups on the fabric and the dye form dative covalent bonds to the metal ion. This forms a chelate complex ion


What is a chelate?

A complex ion in which the metal ion is bonded to two or more atoms on the same molecule


Why is adding fibre-reactive groups to dyes used?

The reactive groups attached to the dye form a bridge between the dye and the fibre


When do instantaneous dipole-induced dipole bonds form between dyes and fabrics?

If the fibre doesn't have many polar groups, it can only bond using instantaneous dipole-induced dipole bonds. These dyes are known as disperse dyes


How are disperse dyes added to fabrics?

The dyes are suspended in water. Then the mixture is added to the fibre and the small dye molecules are able to diffuse into the fabric. They are held there by instantaneous dipole-induced dipole bonds.


What is a chromophore?

The part of a molecule, which is delocalised, that causes it to absorb light.


What types of functional groups modify the chromophore?

Groups that affect the degree of delocalisation, like benzene rings


Name a functional group that makes a dye more soluble.

Sulfonic acid groups on benzene rings


How does the addition of a nitro group to a benzene ring modify the chromophore?

It changes its properties by changing the wavelength of light the chromophore absorbs, thereby changing the colour of the mixture.


Which functional groups can affect a dye's ability to bond to fibres?

The addition of -OH and -NH2 groups mean that more H bonds can form between the dye and the fibre.
The addition of ionic groups like SO3- mean that more ionic bonds can form between the dye and the fibre.


Define the term 'triglyceride'

An ester molecule formed by the esterification of glycerol by three fatty acids


Why are triglycerides also known as triesters?

The systematic name of glycerol is propan-1,2,3-triol, and so can form three ester linkages to carboxylic acids.


What are two examples of triglycerides?

Fats and oils


What is the main difference between fats and oils?

Fats are solid at room temperature and oils are liquid at room temperature


Describe the hydrolysis of triglycerides.

They are heated with concentrated sodium hydroxide to give glycerol and the sodium salts of the fatty acids. The fatty acids are then released from their salts by adding dilute HCl.


Explain why fats and oils aren't soluble in water (4 marks)

-Intermolecular bonds in fats/oils are instantaneous-induced dipole
-Intermolecular bonds in water are hydrogen bonds
-Only instantaneous-induced dipole/permanent-induced dipole are possible between water and fats/oils
-Energy released when fat/oil dissolved isn't enough to break bonds in solute and solvent