F335 - Colour By Design

Question 1

Conditions and reagents for Hydrolysis of Esters

Answer 1

Heating under reflux with moderately concentrated sodium hydroxide solution.

Question 2

What is a conjugated system?

Answer 2

A system with alternate C=C and C-C bonds. The delocalised electrons in this system require less energy to get excited so will absorb UV/Visible frequencies.

Question 3

If a substance ABSORBS blue and green light, what colour will it appear in white light?

Answer 3

Orange

Question 4

How is the colour of substance found from an absorption/wavelength graph?

Answer 4

The wavelength for which absorption is greatest is found. The colour of the substance is the complementary colour of this wavelength.

Question 5

How does gas liquid chromatography work?

Answer 5

• Stationary phase: a non volatile liquid coated on the surface of finely divided solid particles.
• This material is packed inside a long thin column, which is coiled in an oven.
• Mobile phase: An unreactive carrier gas (Often nitrogen) carries the mixture through the column.
• Components emerge from the column, peak is recorded on the chromatogram.
• The area under the peak is proportional to the amount of component in the mixture. The time that a component takes to emerge is called the retention time.

Question 6

Does benzene react with bromine water?

Answer 6

No. Benzene does not contain any carbon carbon double bonds, the bonds are delocalised therefore they do not react with bromine water. The bromine water does not turn from brown to colourless.

Question 7

What type of reactions do a arenes normally undergo? And why?

Answer 7

Benzene will normally undergo substitution reactions and rarely addition reactions. Substitution reactions keep the delocalised electrons structure where as addition would destroy this structure. This means the vast majority of benzene reactions are electrophilic substitutions.

Question 8

Reagents and conditions for nitration of benzene.

Answer 8

Benzene and concentrated nitric acid mixed with concentrated sulphuric acid. Temperature kept below 55°C.

Question 9

Reagents and conditions for sulphonation of benzene.

Answer 9

Benzene and concentrated sulphuric acid. Heat under reflux for several hours.

Question 10

Reagents and conditions for chlorination of benzene.

Answer 10

Benzene and chlorine and anhydrous aluminium chloride. At room temperature.

Question 11

Reagents and conditions for bromination of benzene.

Answer 11

Benzene and bromine and anhydrous iron (III) bromide. Room temperature.

Question 12

Reagents and conditions for Alkylation of benzene.

Answer 12

Benzene and chloroalkane and anhydrous aluminium chloride. Heat under reflux.

Question 13

Reagents and conditions for acylation of benzene.

Answer 13

Benzene and acyl chloride and anhydrous aluminium chloride. Heat under reflux.

Question 14

Characteristics and examples of Friedel-Crafts reactions.

Answer 14

• add carbon sidechains to a benzene ring, which can then be modified further.
• involve a halogen carrier.
• Alkylation and acylation are examples of this.

Question 15

Reagents and conditions for formation of diazonium ions. (Diazotisation)

Answer 15

Phenylamine dilute hydrochloric acid, sodium nitrate (III). Temperature kept below 5°.

Question 16

Formation of azo compounds (coupling reaction).

Answer 16

diazonium Ion and Phenylamine (coupling agent).

Question 17

Affect of adding SO3 Na to chromophore.

Answer 17

The solubility of the dye in water is improved, due to the ionic group-it can form ionic bonds with a protein fibre such as wool.

Question 18

Affect of adding NH2 or NR2 to a chromophore.

Answer 18

The colour of the dye is modified or enhanced.

Question 19

Why are transition metal ions coloured?

Answer 19

Electrons in the D orbitals can be excited. When a transition metal ion is surrounded by ligands the D orbitals are split into two different energy levels. Electrons in the lower energy level can be excited to the higher energy level. The excitation energy required corresponds the absorption of visible light.

Question 20

Factors that affect the excitation energy and therefore the colour of the complex.

Answer 20

• The type of ligand
• The shape of the complex-octahedral or tetrahedral.
• The coordination number of the complex.
• The charge on the central transition metal ion.

Question 21

How is nitrous acid made?

Answer 21

Reacting sodium nitrate (III) and hydrochloric acid.