Colour by Design Flashcards Preview

Chemistry OCR B Alevel > Colour by Design > Flashcards

Flashcards in Colour by Design Deck (45)
Loading flashcards...
1
Q

what are the 3 bonds which can attach a dye to fambric?

A

intermolecular bonds

ionic bonds

covalent bonds

2
Q

which 2 groups modify a chromocaphore?

A

OH and NH2 as they contain lone pairs in p orbitals which add to the delocalised system

3
Q

what group does cotton have to make bonds to and hence what type of bond do dyes make to it?

A

OH groups which form hydrogen bonds with amine groups (to the nitrogen)

4
Q

what groups do nylon, wool and silk fibres have?

A

amine groups

5
Q

how can ion bonds form between a dye and a fabric?

A

between NH3+ (fabric in acid conditions) and sulponate group on the dye

6
Q

what holds together dye wh=ith carboxylic acid groups to a dye with amine groups?

A

ionic interactions - becomes COO- NH2+

7
Q

what is a chromophore?

A

delocalised electron systems in molecules that give them their colour

8
Q

what happens when you change the chromophore?

A

the colour changes, the longer the delocalised system, the smaller the energy gap to lower frequency of light absorbed

9
Q

what groups make dyes more soluble?

A

ionic groups such as sulphonium

10
Q

what are arenes?

A

compounds that contain atleast 1 bezene ring

11
Q

what properties does the delocalisation give aromatic compounds

A

they are more stable (as negative charge is more spread than if it were in localised double bonds)

so addition reactions would need to take out electrons from the stablised ring to form new bonds

so substitution more likely to happen as the stability of the delocalised electrons is preserved - this is often slow however

12
Q

what are the 2 common representations of benzene?

A

kekule and hexagon with circle in middle

13
Q

what shape is benzene?

A

planar ring with bond angles of 120

14
Q

what are the 3 bits of evidence against kekules structure?

A

doesn’t react with bromine water to go colourless

bond lengths are actually identical

the enthalpy change of hydrogenation of benzene is less than 3 times the hydrogenation of cyclohexene (as more energy needed to break bonds as the delocalised pi system makes it more stable so more positive enthalpy change).

15
Q

what are the 5 electrophillic substitution reactions that benzene undergoes?

A

halogenation

nitration

sulfonation

alkylation

acylation

16
Q

what are the conditions and reagents for halogenation?

A

halogen

AlX3 -(e.g AlCl3)

anhydrous reflux

17
Q

what are the conditions and reagents for nitration?

A

concentrated nitric acid (HNO3)

concentrated sulphuric acid

below 55 degree celcius

18
Q

what are the conditions and reagents for sulfonation?

A

concentrated sulfuric acid

reflux

19
Q

what are the reaction conditions and reagent for freidal crafts acylcation?

A

acyl chloride

AlCl3

anhydrous reflux

20
Q

what are the reaction conditions and reagent for freidal crafts alkylation?

A

haloalkane

AlCl3

anhydrous reflux

21
Q

what are the reagents and conditions for diazotisation ?

A

nitrous acid (HNO2) or NaNO2 +HCl(dilute)

<5 degrees celcius

22
Q

what are the reagents and conditions for coupling reaction?

A

NaOH

<5 degrees celcius

23
Q

what are the 2 steps needed to make an azo dye?

A

diazotization and coupling reaction

24
Q

what is the mechanism of a coupling reaction?

A

electrophillic substitution

25
Q

why cant ketone be oxidised?

A

no hydrogen to be removed

26
Q

what mechanism occurs when carbonyls react with cyanide ions and what is formed?

A

nucleophillic addition

forms a cyanohydrin

27
Q

what are the 3 tests for aldehydes?

A

fehlings solution
positive test goes from blue solution to red precipitate

tollens reagent
forms a silver mirror when warmed gently from colourless

add acidified sodium dichromate
goes orange to green

28
Q

why can organic molecules absorb ultraviolet or visible light?

A

as by absorbing the energy proportional to the energy gap you can excite electrons to higher energy levels (to higher empty molecular orbitals)

29
Q

why are chromophores coloured?

A

the delocalised pi systems make the energy gap smaller so they need to absorb lower frequency to be excited as deltaH= hv.

as delocalisation increases , enrgy gap decreases and the frequency of light absorbed drops.

30
Q

what is the mobile phase is gas liquid chromatography?

A

carrier gas - an inert gas such as Ar or N2

31
Q

what is the stationary phase in gas liquid chromatography?

A

porous solid support soaked in a liquid with high boiling point

32
Q

what are the 4 main stages of gas liquid chromatography?

A

sample is vaporised and injected into the carrier gas

sample moves through the column

samplr is detected and retention time is measured

retention time is compared to known data base

33
Q

what is the retention time?

A

time taken from injection to detection

34
Q

if the retention time is very short what physical properties does this suggest?

A

insoluble in the stationary phase

volatile (stays as a gas)

35
Q

what extra analysis can make glc results more accurate?

A

similar compounds have similar retention times so use mass spec to find Mr and fragmentation patterns

36
Q

Compare the different reactivities of benzene and alkenes towards chlorine.

A

In benzene, π electrons are delocalised/spread out (1)
In alkenes, π electrons are concentrated between 2 carbons (1)
Electrophiles attracted more to greater electron density in alkenes (1)

37
Q

describe the bonding in benzene?

A

p-orbitals overlap (1)
above and below the ring (1)
(to form) π-bonds / orbitals (1)
(π-bonds / electrons) are delocalised (1)

38
Q

what does a curly arrow represent?

A

a pair of electrons

transferred

covalent bond breaks/ forms

39
Q

what is an electrophile?

A

accepts a pair of electrons

40
Q

how does an electron carrier allow halogenation to take place?

A

it induces a permanent dipole on chlorine, forming Cl+

41
Q

describe the bonding and structure of benzene

A
p-orbitals overlap (1)
 above and below the ring (1)
 (to form) π-bonds / orbitals (1)
any of the first three marks are available from a labelled
diagram
eg
bonds
 (π-bonds / electrons) are delocalised (1)
4 marks
42
Q

describe how the bonding in bezene accounts for the fact that bond lengths are equal

A

one electron from each carbon is delocalised so all bonds are equal

43
Q

explain in terms of delocalisation and energy levels why dye is coloured and benzene is yellow

A
  1. Electrons move to a higher energy level 
  2. absorbing em radiation Δ E = hv
  3. Yellow dye has more delocalisation/ larger chromophore
    AND energy levels are closer together/ Δ E is smaller 
  4. Energy absorbed is at lower visible frequencies 
  5. complementary colour is transmitted
44
Q

explain why compounds with an aromatic ring usually form substituted derivatives rather than adition compounds

A

(aromatic compounds have) delocalised electrons that
are lost on addition AND retained on substitution 
(loss of delocalisation causes) less stability AW 

45
Q

what inorganic substance forms when fehilings solution is added to an aldehyde?

A

Cu2O