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Chemistry 3.3 Organic chemistry > alcohols > Flashcards

alcohols Flashcards

(61 cards)

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1
Q

what is the general formula for alcohols?

A

Cn H2n+2 O

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2
Q

what is the functional group of alcohols?

A

R-OH

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3
Q

what can we classify alcohols as?

A

primary secondary or tertiary

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4
Q

what are functional group isomers of alcohols?

A

ethers (hydrogen from R-OH replaced with another R group)

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5
Q

what is hydrolysis?

A

breaking a bond using water

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6
Q

what are the three mechanisms of making alcohols?

A

-hydrolysis of organic hydrogensulfates
-nucleophilic substitution
-electrophilic addition (steam hydration of ethene)

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7
Q

how do we get alcohols from organic hydrogensulfates?

A

they are easily hydrolysed so hydrolyse using warm water to form alcohols

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8
Q

what is regenerated at the end of hydrolysis of organic hydrogensulfates and what does this act as?

A

sulfuric acid (H2SO4) so it acts as a catalyst

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9
Q

what are the 3 uses of alcohols?

A

-alcoholic drinks
-solvents
-chemical feedstock (used to make other chemicals)

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10
Q

what kind of boiling points do alcohols usually have and why?

A

high because they form hydrogen bonds with each other

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11
Q

why are only some alcohols soluble?

A

ones with a lower Mr are soluble in water because they can form hydrogen bonds with water

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12
Q

what are the conditions for making an alcohol via nucleophilic substitution?

A

aqueous sodium hydroxide, warm

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13
Q

what reaction is used in industry to produce ethanol and what mechanism does it use?

A

steam hydration (addition of water) of ethene

electrophilic addition

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14
Q

what are the conditions for steam hydration of ethene?

A

steam (300 degrees), pressure of 60atm and phosphoric acid catalyst (H3PO4)

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15
Q

what type of reaction is steam hydration of ethene and what does this mean for the yield?

A

it is reversible and the yield is very low

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16
Q

how is yield improved by steam hydration of ethene?

A

any unreacted ethene gas can be recycled and increases the overall yield

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17
Q

what are some advantages of using steam hydration of ethene?

A

-product is pure (No waste product including CO2)

-we can manipulate the reversible reaction to increase yield

-higher temperature, therefore, fast rate of reaction

-can recycle unused reactants such as ethene gas.

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18
Q

what are some disadvantages of steam hydration of ethene?

A

-reversible reaction so not 100% yield

-ethene is from crude oil contributing to environmental pollution. Thermal cracking of crude oil requires energy.

-higher temps required so higher energy consumption

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19
Q

what is the alternative industrial method for making alcohols that doesn’t use a mechanism?

A

fermentation

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20
Q

what are the reagents of fermentation?

A

yeast and glucose (C6H1206)

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21
Q

what are the conditions for fermentation?

A

30-40 degrees, aqueous, anaerobic

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22
Q

what is the role of yeast in fermentation?

A

catalyst

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23
Q

why is it important that fermentation occurs in anaerobic conditions?

A

yeast won’t ferment in oxygen and oxyegn would cause the ethanol to be oxidised to ethanal

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24
Q

why do we use 30-40 degree temperatures for fermentation?

A

compromise because too high temp causes yeast to denature and not ferment

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25
what is the equation for fermentation?
C6H1206 (aq) --------> 2 C2H5OH (aq) + 2 CO2 (g)
26
when does fermentation stop and what do we do once it has stopped?
when the reaction mixture contains 15% ethanol we use simple distillation
27
during simple distillation, where does water go in and out of the condenser?
in at bottom out at top
28
what is the type of alcohol we make during fermentation and what does this term mean?
biofuel biofuel is fuel that is derived from biomass- that is, plant, algae material or animal waste
29
what do some people argue about fermentation and the production of bioethanol that is not true?
that it is carbon-neutral
30
what does carbon-neutral mean?
uses the same amount of CO2 from the atmosphere in its production as is released into the atmosphere when used
31
what can we give in support of why fermentation is supposedly carbon neutral?
3 equations photosynthesis of glucose 6 CO2 + 6 H2O -------> 6O2 + C6H12O6 fermentation of glucose C6H12O6 --------> 2 C2H5OH +2 CO2 combustion of ethanol 2 C2H5OH + 2 O2 --------> 4 CO2 + 6 H2O total = 0 CO2 released
32
why is fermentation not carbon neutral? (3)
-we produce NH3 (ammonia to use for plant fertiliser) which uses a lot of energy and releases CO2 -transport of plants and processing plants requires combustion of fuel which releases CO2 -processing of plants requires energy.
33
what can we (acid catalysed) eliminate alcohols to?
alkenes
34
what are the reagents and conditions for elimination of alcohols?
concentrated sulfuric acid or phosphoric acid, heat (under refluc)
35
what is removed and formed during elimination of alcohols?
OH removed H atom on an adjacent carbon removed double bond formed between two C atoms
36
why is elimination of alcohols useful?
can get alkenes without needing to obtain alkenes from fractional distillation followed by thermal cracking. these alkenes can be used to make polymers in future it may become more economical to produce ethene from ethanol made by fermentation
37
what is oxidation and reduction in terms of alcohols?
oxidation : gain of oxygen and loss of H atoms (electrons) reduction: loss of oxygen and gain of H atoms (electrons)
38
what can alcohols be oxidised by doing?
oxidising agents such as acidified potassium dichromate (VI) (it is acidified with dilute sulfuric acid)
39
what do oxidising agents do?
cause something (alcohol) to gain an oxygen but loses one itself in other words; oxidises something but itself is reduced
40
what colour change do we observe when acidified potassium dichromate (VI) acts as an oxidising agent?
orange to green
41
what does the type of organic product obtained via oxidation of an alcohol depend on?
the structure of the alcohol used
42
what are possible oxidation products of primary, secondary and tertiary alcohols?
primary: aldehyde or carboxylic acid secondary: ketone tertiary: NOT OXIDISED as no hydrogen atoms on C with OH
43
what is the apparatus needed to oxidise primary alcohols to aldehydes?
simple distillation to produce an aldehyde anti-bumping granules in flask
44
what do anti-bumping granules do?
prevent the formation of large bubbles forming that result in violent boiling
45
what is the apparatus needed to oxidise primary alcohols to carboxylic acids?
reflux as the boiling point of carboxylic acids is much higher than due to hydrogen bonding anti-bumping granules
46
how we do test for an aldehyde?
-tollens reagent (silver mirror test) it is a colourless solution containing Ag+ ions -fehling's solution, it is a blue solution of copper (II) ions both are weak oxidising agents
47
describe how to use tollens reagent to test for an aldehyde?
put 2 cm3 silver nitrate in a test tube. add a few drops NaOH to form a brown precipitate. Add dilute NH3 to dissolve precipitate. warm this with the unknown
48
what is a positive test with tollens?
a silver mirror forms and a carboxylic acid has been made from the aldehyde
49
describe how to use fehling's solution to test for an aldehyde?
add 2cm3 of fehlings to unknown and warm in water bath
50
what is a positive test with fehlings?
a brick red precipitate forms due to Cu2O and a carboxylic acid has been produced from an aldehyde
51
how do we test for carboxylic acids using tollens and fehlings?
tollens and fehlings give a negative result
52
how do we test for carboxylic acids?
sodium carbonate (Na2CO3) or sodium hydrogen carbonate (NaHCO3) produces CO2 gas which we bubble through limewater and observe a milky white emulsion (fizzing/ bubbling)
53
what are the products of testing for a carboxylic acid?
carbon dioxide, salt and water
54
why is there no test for ketones?
can't be oxidised further
55
how do we test for an alcohol?
react with sodium to produce a salt and hydrogen observation; fizzing
56
what are the bond angles in alcohols and why?
all the H-C-H bonds and C-C-O bonds are 109.5 (tetrahedral), because there are 4 bonding pairs of electrons repelling to a position of minimum repulsion the H-O-C bond is 104.5 because there are 2 bonding pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion. Lone pairs repel more than bond pairs so bond angle reduced.
57
in distillation, what can be done to increase yield of distillate?
only collect the distillate at the desired b.p. of the aldehyde and not higher collection glass can be cooled in ice
58
what is reflux used for?
when heating organic reaction mixtures for long periods of time. the condenser prevents organic vapours from escaping by condensing them ack to liquids.
59
why is the end of the condenser never sealed in reflux?
build up of gas pressure could cause apparatus to explode
60
what is a good thing about producing alkenes from alcohols?
provides a possible use to polymers without using monomers derived from oil
61
What is a general equation for the oxidation of primary alcohols?
RCH2OH + [O] ——-> RCHO + H2O

Chemistry 3.3 Organic chemistry (10 decks)

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