CD  Colour by Design

 

CD1 Synopsis

 

The chemical basis of colour, in pigments, paints and dyes, and the use of chemistry to provide colours to order. Main topics:

• the chemical origins of colour;

• aromatic compounds;

• paints and pigments;

• chemistry in the art gallery: analysing pigments and oils, restoring paintings;

• dyes and dyeing.

 

 

CD2 Learning outcomes

 

Candidates should be able to:

(a)           explain the absorption of ultraviolet light and visible light in terms of transitions between electronic energy levels;

 

(b)           use ultraviolet (u.v.) and visible spectroscopy to help identify unsaturated organic molecules;

 

(c)           recall that colour changes may be associated with the following chemical changes:

 

(i)                 acid-base (indicators),

(ii)                 ligand exchange,

(iii)                 redox,

(iv)            precipitation,

(v)                 polymorphism (different crystal structures);

 

(d)           relate the desirable properties of pigments (such as colour shade, colour intensity, fastness) to relevant properties;

 

(e)           outline the general principles of gas-liquid chromatography (g.l.c.);

 

 

(f)

show awareness of the techniques used to identify the materials used in a painting,

 

including:

 

(i)

gas-liquid chromatography,

 

 

(ii)

atomic emission spectroscopy,

 

 

(iii)

visible spectroscopy (reflection and transmission);

 

(g)

given relevant information, interpret results from analytical techniques used to identify

 

components of unknown materials, such as those used in paintings;

(h)

recall that fats and oils consist mainly of mixed esters of propane-1,2,3-triol with varying

 

degrees of unsaturation;

(i)

describe in general terms the process of oxidative cross-linking by which unsaturated oils

 

harden, and relate to their use as media in oil-based paints;

(j)

recognise arenes and arene derivatives (aromatic compounds);

(k)

 

relate the characteristic properties of aromatic compounds to the delocalisation of electrons  in the benzene ring

(l)

describe and explain the following electrophilic substitution reactions of arenes:

 

(i)

halogenation of the ring,

 

(ii)

nitration,

 

(iii)

sulphonation,

 

(iv)

 Friedel-Crafts alkylation,

 

(v)

Friedel-Crafts acylation;

(m)

describe and explain the formation of azo dyes by coupling reactions involving diazonium

 

compounds;

(n)

describe and explain the structure of a dye molecule in terms of its functional components:

 

chromophore, groups which modify the chromophore, groups which affect the solubility of the dye, groups which attach the dye to the fibre.

 

(o)

 

explain, in terms of intermolecular forces, ionic attractions and covalent bonding, how some dyes attach themselves to fibres.

 

(p)

relate the colour of a dye to the presence of a chromophore, and groups that modify the

 

chromophore, in the dye molecule.