Colour By Design

Question 1

Describe beta-carotene.

Answer 1

Orange colour given to vegetables. Present in leaves, absorbs energy from sunlight.

Question 2

Define a conjugated system.

Answer 2

Alternating double and single bonds.

Question 3

What factors affect colour?

Answer 3

More delocalised electrons, smaller energy gap. Absorption of longer wavelengths.

Question 4

What is the bond angle in benzene?

Answer 4

120.

Question 5

How is cyclohexane formed?

Answer 5

Benzene reacts with hydrogen in an addition reaction.

Question 6

Describe chlorination.

Answer 6

Aluminium chloride catalyst, anhydrous conditions.

Question 7

Describe bromination.

Answer 7

Iron bromide catalyst, heat.

Question 8

Describe alkylation.

Answer 8

Aluminium chloride catalyst, heated under reflux.

Question 9

Describe acylation.

Answer 9

Aluminium chloride catalyst, anhydrous conditions.

Question 10

Describe nitration.

Answer 10

Nitric acid and sulfuric acid, concentrated, less than 55C.

Question 11

Describe sulfonation.

Answer 11

Sulfuric acid, heated under reflux. Produces benzenesulfonic acid, forms salts in alkaline conditions.

Question 12

How are azo functional groups formed?

Answer 12

Diazonium salt + coupling agent.

Question 13

Describe azo groups.

Answer 13

Unstable, diazonium group easily lost forming nitrogen gas. If attached to benzene ring, stabilised. Prepared in ice-cold solutions.
Dissolved in HCl and sodium nitrite, below 5C, diazotisation.

Question 14

Define a chromophore.

Answer 14

Energy levels of delocalised electron system.

Question 15

Describe cationic dyes.

Answer 15

N+ forms ionic bonds with COO-. Applied in alkaline conditions. Relies on hydrogen bonding, easily washed out.

Question 16

Describe colourfast dyes.

Answer 16

Azo modified with trichlorotriazine, attacked by nucleophilic groups reacted with hydroxyl groups, strong covalent bonds.

Question 17

Describe wool and silk.

Answer 17

Protein fibres. Able to be ionised. Strong electrostatic forces, under acidic conditions. Ionic bonding.

Question 18

Describe fibre reactive dyes.

Answer 18

Fast forming, more covalent bonds, trichlorotriazine.

Question 19

Describe disperse dyes.

Answer 19

Insoluble in water, instantaneous induced dipoles.

Question 20

Describe mordanting.

Answer 20

Metal ion joined to dye through dative covalent bonds. Chelate complex ions Al3+ or Cr3+.

Question 21

Describe a triglyceride.

Answer 21

Propane-1,2,3,-triol. Forms 3x H2O. Saturated, cis. Unsaturated, trans.Produces sodium salts with sodium hydroxide.

Question 22

What catalyst is used with hydrogenation?

Answer 22

Nickel.

Question 23

Describe the mobile phase of gas-liquid chromatography.

Answer 23

Inert gas, helium or nitrogen.

Question 24

Describe the stationary phase of gas-liquid chromatography.

Answer 24

A liquid with a high boiling point on an inert porous solid.

Question 25

Describe gas-liquid chromatography.

Answer 25

Sample is injected into a heated column and vaporised with a carrier gas. The carrier gas moves the sample through the stationary phase. Only works on volatile substances.

Question 26

Define retention time.

Answer 26

Time taken for each component to pass through the stationary phase.

Question 27

Describe Fehling’s.

Answer 27

Oxidising agent Cu2+ and a bidentate ligand. Aldehydes are oxidised to carboxylic acids (blue to red)

Question 28

Describe Tollen’s.

Answer 28

Silver oxide in ammonia. Aldehydes are oxidised to carboxylate ions and form a silver mirror.

Question 29

Describe tetrahydroborate.

Answer 29

Reduces aldehydes to primary alcohols and ketones to secondary alcohols.