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A level Chemistry > Chapter 14 - Alcohols > Flashcards

Chapter 14 - Alcohols Flashcards

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1
Q

the OH group?

A

the hydroxyl group, is responsible for both the physical and chemical properties of alcohols

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2
Q

methanol uses?

A
  • high performance fuel bc of its efficient combustion

- an important chemical feedstock - the starting material in many industrial syntheses

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3
Q

ethanol uses?

A

primarily in alcoholic drinks and as a fuel, solvent, and a feedstock

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4
Q

when there are two OH groups?

A
  • suffix is -diol

- -diol does not start with a vowel so the alkane chain name is not shortened e.g. not butan instead of butane

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5
Q

alcohols vs alkanes physical properties?

A
  • when alcohols and alkanes of the same number of C atoms are compared,
  • alcohols are less volatile, have higher melting points, greater water solubility than the corresponding alkane
  • the differences become much smaller as the C chain length inc
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6
Q

bonds in alkanes vs bonds in alcohols?

A
  • alkanes have non polar bonds as C&H have similar electroneg, so molecules = non polar
  • sp induced dipole forces, weak
  • alcohols have polar O-H bond, so mols r polar
  • Hydrogen bonds, much stronger
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7
Q

influence of OH group?

A

as the hydrocarbon chain length inc, the influence of the OH group becomes relatively smaller, solubility decreases

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8
Q

e.g.s of primary alcohols?

A

methanol and ethanol

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9
Q

what is a primary alcohol?

A

the OH group is attached to a C that is attached to 1 alkyl group

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10
Q

when alcohols are oxidised, why is there a colour change from orange to green?

A

-the orange solution containing dichromate (VI) ions is reduced to a green solution containing chromium (III) ions :
C2O7 2- -> Cr3+

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11
Q

when preparing carboxylic acids (full ox)?

A

excess acidified potassium dichromate is used which ensures that all of the alcohol is oxidised

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12
Q

when preparing an aldehyde ? is used, but when preparing a carboxylic acid ? is used

A
  • aldehyde: use distillation to remove the aldehyde from the reaction mixture
  • carboxylic acid: reflux
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13
Q

what colour change will happen when acidified potassium dichromate is added to a tertiaty alcohol?

A

stays orange

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14
Q

are alcohols saturated or unsaturated?

A

sat (single bonds only)

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15
Q

general formula?

A

CnH2n+1OH

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16
Q

Properties of alcohols?

A
  • gradation in physical properties - BP ⬆ w C chain length

- have similar chemical properties

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17
Q

Classed as ?

A

Primary, Secondary, tertiary

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18
Q

Trend in BP?

A
  • As chain length ⬆, the molecules get longer, there are more SA contact points, so stronger induced dipole forces, so stronger + more induced dipole forces means more energy required to overcome & BP ⬆
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19
Q

SOLUBILITY?

A
  • Soluble in polar solvents - ‘LIKE DISSOLVES LIKE’
  • The OH gr is polar, H2O mols r polar
  • alcs can form H bonds w H2O mols
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20
Q

vs. alkanes?

A
  • higher BP than alkanes - alchols can form H bonds, e.g. propanol has higher BP than propane
  • Less Volatile - As BP are ⬆ than alkanes, less volatile
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21
Q

what does volatile mean?

A

the tendency of a substance to evaporate

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22
Q

?

A

thru Ox, alcohols lose atoms of H - lost from OH and the H opposite the OH

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23
Q

why can tertiary alc not be ox?

A

OH present, but no H bonded to the C that’s bonded to the OH

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24
Q

Alcohols can b combusted as ?

A

a fuel source

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25
Q

what happens in dehydration of an alcohol?

A
  • an elimination reaction
  • H2O lost
  • alkene forms bc a π bond forms between the adjacent C atoms
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26
Q

2 ways to make ethanol?

A
  • Industrial production

- fermentation

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27
Q

Industrial production?

A

= hydration of ethene
Reagents/ Conditions: Ethene is passed over a phosphoric acid catalyst along w steam at 330 degrees C (has to be over 100) + under high pressure

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28
Q

hydration of ethene to form ethanol equation?

A

ethene + water -> (phosphoric acid catalyst on arrow) ethanol
- C2H4(g) + H2O (g) -> C2H5OH(l)

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29
Q

+s of industrial production of ethanol?

A

+ the hydration of ethene is a much faster reaction producing a high conc of ethanol
+ continous process
+ unreacted ethene and H2O recycled
+ 100% atom economy
+ High % conversion to C2H5Oh >95%, catalyst reusable

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30
Q

-s of industrial production of ethanol?

A
  • requires conditions that take a lot of energy to sustain

- uses a non renewable starting materual - oil

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31
Q

fermentation?

A

Reagents/ Conditions: yeast, air kept out of fermentation vessels to prevent Ox of the ethanol to ethanoic acid - anaerobic
- temp carefully controlled, too low = slow R, too high = yeast enzymes won’t work effectively - 35 degrees used

32
Q

fermentation equation?

A
  • anaerobic respiration

- C6H12O6 -> (yeast on arrow) 2C2H5OH(aq) +2CO2(g

33
Q

+s of fermentation?

A

+ uses renewable starting materials

+ low energy costs

34
Q

-s of fermenatation?

A
  • batch process, labour intensive, produces a low conc impure sol o ethanol
  • alc needs separating
  • 15% alcohol (yeast denatures)
35
Q

what is the filtrate?

A

the liquid that passes thru the filter paper

36
Q

what is the residue?

A

the bit left over in the filter paper

37
Q

what are antibumping granules?

A

little pieces of an unreactive material that allow the mixture to boil evenly

38
Q

distillation flask can be either?

A

round or peark shaped

39
Q

what does the adaptor do?

A

‘T shaped’ - connects distillation flask to condensor

40
Q

what does the test tube do?

A

collect distillate

41
Q

why can you collect the ethanol when the distillation flask is heated to 80 degrees?

A
  • the ethanol will evaporate
  • as the H bonda and induced dipole forces between the ethanol molecules are weaker than the H bonds between H2O molecules
  • so the bonds between ethanol molecules break at a lower temp as less energy required
42
Q

what is the distillate?

A

the liquid that collects

43
Q

making ethanol by fermentation what is the residue, filtrate/

A 
residue = yeast - too large to pass thru filter paper 
filtrate = ethanol + H2O + dissolved glucose
44
Q

what happens when you ignite the distillate/

A

burns with an almost invisible blue flame suggesting its ethanol as H2O and glucose are NOT flammable, must be ethanol if it burns

45
Q

what can distillation be used to do?

A

seperate the most volatile liquids from a mixture

46
Q

what does volatile mean?

A

a substance w a low BP that easily changes to a gas

47
Q

in a distillation flask where does the water go and out and where does it come in?

A

water out at top, in at bottom

48
Q

why must the water go in at the bottom of the flask and come out at the top?

A

so the outer wall of the condenser can completely fill w water so the vapours can condense

49
Q

if fermentation was carried out under reflux (upwards appartus instead of reflux) what would happen?

A
  • the mixture would boil but no seperation of the alcohol would take place. No liquids would evaportae -> when the liquids evaporate , the vapours move up into the condenser and change back into iquids which drip down into the flask
50
Q

what does heating under reflux allow?

A

liquids to be heated for a long period of tim w/o any loss due to evap

51
Q

why are many organic chemicals heated under reflux?

A
  • organic chemicals are all volatile

- w/o refluxing, they would evaporate when we heated them to react

52
Q

Hydrogen bond definition?

A

the strongest type of IMF. A permanent dipole force forms between delta + H on one molecule and the lone pair of e-s on the delta - O or delta - N or delta - F of a neighbouring molecule

53
Q

distillation flask definition?

A

a round or pear shaped glass container that contains the mixture of chemicals

54
Q

filtrate definition?

A

the liquid that passes thru the filter paper, it contains dissolved chemicals

55
Q

anti-bumping granules definition?

A

an unevenly shaped piece of solif added to make liquids boil more calmly

56
Q

Distillate definition?

A

the liquid that has been condensed from a vapour and collected

57
Q

IMF definition?

A

a weak force of attraction between molecules

58
Q

distillation definition?

A

heating a liquid to evaporate it, then cooling the vapour in a condenser & collecting it - a sep tech.

59
Q

reflux definition?

A

continual boiling and condensing of liquids to ensure the reaction takes place w/o loss of the liquids due to evaporation

60
Q

volatile definition?

A

a liquid w a low BP that readily changes into a gas

61
Q

compare and explain the solubility of pentan-1-ol and methanol in H2O?

A
  • both soluble as both form H bonds to H2O
  • the short C chain in Methanol will not prevent methanol molecules from bonding to H2O molecules so methanol will be soluble in H2O
  • the non polar C chain in Pentanol will bond to other C5H11 chains by induced dipole forces. The Pentanol molecules will stay bonded to each other and not mix w H2O
62
Q

reactions: combustion?

A
  • alcohols burn releasing energy
  • Reagent: O2
  • e.g. C2H5OH (l) + 3O2(g) -> 2CO2(g) + 3H2O(l)
  • this reaction is exothermic, releasing a large quan. of energy in the form of heat
  • as the no. of C atoms in the chain ⬆, the quan of heat released per mole also ⬆
  • plentiful supply of O2 needed
63
Q

reactions: reaction w Na forming H2(g) and a salt e.g. sodium ethoxide (this is the chemical test for an alcohol)

A

ethanol + sodium -> sodium ethoxide + hydrogen
R: Na (s)
Equation for propanol: CH3CH2CH2OH(l) + Na(s) -> CH3CH2CH2ONa(aq) + 1/2 H2(g)
-> sodium propoxide is formed (an ionic salt)
the slow release of H2 is used as a test for OH

64
Q

reactions: dehydration of an alcohol to form an alkene?

A
  • isomers possible
  • conditions: acid catalyst (conc H2SO4or H3PO4), heat under reflux
  • reagent: none
  • cycloalkenes can also be formed from the dehydration of cycloalcohols
  • H2O AND ALKENE FORMED
65
Q

distillation vs reflux position?

A

condenser in the vertical position is known as the reflux position and when condenser is sideways = distillation position

66
Q

reactions: substitution of the OH group for a halogen, forming a haloalkane?

A
  • the alc is heated under reflux w H2SO4 & a Na or K halide. These reagents form the H halide.
  • OH group is swapped for a halogen
  • R: NaBr + H2SO4
    c: Under reflux
67
Q

reactions: substitution of the OH group for a halogen, forming a haloalkane - equations?

A

NaBr(s) + H2SO4(aq) -> NaHSO4 (aq) + HBr(aq)

HBr + CH3CH2CH2OH -> CH3CH2CH2CH2Br +H2O- the H halide reacts w the alc

68
Q

the OH group should have its own what in a skeletal formula?

A

LINE, can’t just write it on the last C

69
Q

reactions: substitution of the OH group for a halogen, forming a haloalkane -overall equation?

A

CH3CH2CH2CH2OH + NaBr + H2SO4 -> CH3CH2CH3CH2Br + H2O + NaHSO4

70
Q

when can dehydration give 2 possible products?

A

when there is 2 ways of removing a molecule of water - where the molecule is removed bond determines the position of the C=C

71
Q

What are the reagents and conditions used for Ox of alcs?

A
  • acidified Potassium or Sodium Dichromate (H2SO4 & K2CR2O7) which changes colour from orange -> green during reaction +Ox agent [O], conditions vary depending on class
72
Q

Ox of a primary alc?

A
  • can be either mild or full
  • mild under distillation & forms an aldehyde - al ending
  • full under reflux and forms carboxylic acid - oic acid
  • water is always formed - mild Ox needs 1[O] and full needs 2[O]
73
Q

aldehyde FG?

A

CHO

74
Q

CA FG?

A

COOH

75
Q

Ox of a 2ndry alc?

A
  • under reflux

- ketone formed - none ending

76
Q

What is the difference between ketone and aldehyde?

A

Aldehyde C=O is on the end of the mol and is bonded to a H, Ketone is not bonded to a H and is the middle

77
Q

Ox rememver?

A

2 H’s have to be lost from same C + react w {O} to form the water

A level Chemistry (39 decks)

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