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OCR B A Level Chemistry > colour by design > Flashcards

colour by design Flashcards

1
Q

What are the main features of the stationary phase used in gas-liquid chromatography?

A

The stationary phase is a small amount of liquid with a high boiling point, held on a finely divided inert porous solid support.

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2
Q

What are the reagents and conditions for the synthesis of a diazonium salt?

A

Nitrous acid + phenylamine + HCl -> benzenediazonium chloride

<5 degrees

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3
Q

How and why is HNO2 made in situ?

A

It is unstable

Sodium nitrile (NaNO2) + HCl

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4
Q

What are the reagents for a coupling reaction?

A

Phenol + NaOH + chilled benzenediazonium chloride

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5
Q

How is the colour of an azo dye produced?

A

The result of light absorption by the delocalised electron system

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6
Q

What is an electrophile?

A

A molecule/ion with a positive or partial positive charge that is attracted to an area of high electron density.

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7
Q

What does a coupling agent do?

A

Increases the electron density

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8
Q

what is the light you see with regards to solutions?

A

transmitted light

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9
Q

what are complementary colours?

A

two colours which combine to form white light

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10
Q

why might a compound absorbing high energy be colourless?

A

it is absorbing UV light, which is out of the visible spectrum of light

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11
Q

what is a conjugated system?

A

a molecule containing a series of alternating double bonds.

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12
Q

why are conjugated systems considered delocalised?

A

the electrons in these p-orbitals which make up the pi bond of each double bond are able to spread out.

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13
Q

state and explain a factor which can affect colour of a compound

A
  • the more electrons that are delocalised = smaller energy gap
  • smaller energy gaps result in the absorption of longer wavelengths of light absorbed
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14
Q

give the features of the delocalised model

A
  • regular planar hexagon
  • bond angles 120
  • all c-c bonds same length
  • a more delocalised substance is more stable
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15
Q

why is the enthalpy change of hydrogenation for benzene different to that of the kekule model?

A

the value for benzene is much less exothermic

the delocalised model is more stable, and much less energy is released.

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16
Q

define chelate

A

a chelate is a complex ion in which the metal ion is bonded to two or more atoms in the same molecule

17
Q

what is a fibre reactive dye?

A

a dye molecule containing a reactive group (such as Cl) that can bond covalently to molecules of the fibre. bonds to molecules with frequent OH or NH2 groups.

18
Q

what is a disperse dye?

A

when the dye molecule is small and non-polar

  • it is suspended in water rather than dissolved
  • weak instantaneous dipole-induced dipoles form between dye and fibre
19
Q

what type of bonding is present between a dye molecule with ionic groups and a polymer with pos. charged ionic groups?

A

ionic bonds to nylon, silk or wool molecules

20
Q

what type of bonding is present between a linear dye with frequent NH2 groups, and a polymer with frequent OH groups?

A

hydrogen bonding- cotton

21
Q

what is a triglyceride?

A

an ester molecule formed by the reaction of propan-1,2,3-triol and 3 fatty acid molecules

22
Q

how can you identify a fat?

A

by breaking it down into glycerol and fatty acids. heat with c. NaOH to produce the sodium salts of the fatty acids, then react with HCl to isolate the fatty acids.

23
Q

what are the reagents and conditions required for the synthesis of nitrobenzene from benzene?

A
  • c. H2SO4 + HNO3 (nitrating mixture)

- temperature >55 degrees unless multiple substitutions desired

24
Q

what is the electrophile in the nitration of benzene?

A

NO2+

25
Q

what are the reagents and conditions required for the synthesis of benzenesulfonic acid from benzene?

A
  • benzene and c. sulfuric acid

- heated under reflux for several hours

26
Q

What is an elimination reaction

A

A small molecule is removed from a larger one, leading an unsaturated molecule

27
Q

What is a condensation reaction?

A

Two molecules react to form a larger molecule and a small molecule which is removed

28
Q

What is fehlings solution and what does it test for?

A
  • Copper(II) ions dissolved in NaOH

- is reduced to a brick red copper oxide precipitate in the presence of aldehydes.

29
Q

What is tollens reagent, how is it prepared and what does it test for?

A
  • Ag(NH3)2+

- silver nitrate + dilute NaOH -> brown precipitate -> add dilute NH3

30
Q

by what measurement are compounds identified by using Gas-Liquid Chromatography?

A

retention time

OCR B A Level Chemistry (12 decks)

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