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chemistry a- level > Alcoholes > Flashcards

Alcoholes Flashcards

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1
Q

For the partial reaction of primary alcoholes give the reaction in words (change in functional group) , the conditions and the reagents that should be used.

A

Reaction: primary alcohol goes to aldehyde
Reagent: potassium dichromate (VI) solution and dilutesulfuricacid.
Conditions: (use a limited amount of dichromate) warm gently and DISTIL out the aldehyde as it forms:

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2
Q

For the partial reaction of primary alcoholes give the reaction in words (change in functional group) , the conditions and the reagents that should be used.

A

Reaction: primary alcohol goes to aldehyde
Reagent: potassium dichromate (VI) solution and dilute sulfuric acid.
Conditions: (use a limited amount of dichromate) warm gently and DISTIL out the aldehyde as it forms:

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3
Q

When writting the structural formula of an aldehyde how must it be correctly written so it properly represents an aldehyde.

A

Write the ending as CHO (Never write COH)

For example CH3CH2CHO.

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4
Q

Describe and explain what is observed when Propan-1-ol is oxidised to propanal.

A

Microscopic change : the orange dichromate ion (Cr2O72-) reduces to the green Cr3+ion.
Macro Observation: Orange to green colour change.

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5
Q

How should any oxidisation equation be writen and write an equation using structural formula and displayed formula for the oxidation of propan-1-ol with K2Cr2O17 with the product being distilled off as it formes.

A

CH3CH2CH2OH + [O] INTO CH3CH2CHO + H2O

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6
Q

How should any oxidisation equation be writen and write an equation using structural formula and displayed formula for the oxidation of propan-1-ol with K2Cr2O7 with the product being distilled off as it formes.

A

Write the oxidation equations in a simplified form using [O] which represents O from the oxidising agent.
SEE PIC FOR DISPLAYED.
CH3CH2CH2OH + [O] INTO CH3CH2CHO + H2O

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7
Q

What in general is distilation used for.

A

In general used as separation technique to separate an organic product from its reacting mixture.

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8
Q

When distiling off an aldehyde from the partial oxidation of an alcohol how could you maximise the yield of aldehyde produced.

A

In order to maximise yield collected, only collect the distillate at the approximate boiling point of the desired aldehyde and not higher.

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9
Q

List the 5 things should be included on a distilation apparatus. Draw this labbled apparatus. What should you not do when drawing the set up.

A
  • Round bottom Flask
  • Some source of heat
    -Thermometeer
    -Leibig condenser
  • Colection flask
    See picture of the distilation apparatus.
    Don’t draw lines between flask, adaptor and condenser and across thermometer.
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10
Q

When distiling off an aldehyde from the partial oxidation of an alcohol how could you maximise the yield of aldehyde produced.

A

In order to maximise yield collected, only collect the distillate at the approximate boiling point of the desired aldehyde and not higher.
Also The collection flask can be cooled in ice to help improve the yield of distillate.

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11
Q

Why are electric heaters often used to heat organic chemicals.

A

Electric heaters are often used to heat organic chemicals. This is because organic chemicals are normally highly flammable and could set on fire with a naked flame.

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12
Q

Why does the water go in to the bottom of the condenser to go against gravity.

A

This allows more efficient cooling and prevents back flow of water.

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13
Q

Write an oxidation equation for propan-1-ol being heated under reflux with exess chromate and concentrated H2SO4. What type of oxidation is this. What is observed for this.

A

CH3CH2CH2OH + 2[O] INTO CH3CH2COOH + H2O.
Propan-1-ol goes into propanoic acid and water. This is the full oxidation of a primary alcohol.
The same observation and microscopic thing occurs as with partial oxidation of a primary alcohol.
Observation: the orange dichromate ion (Cr2O72-) reduces to the green Cr3+ion.

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14
Q

When and how does reflux work.

A

Reflux is used when heating organic reaction mixtures for long periods. The condenser prevents organic vapours from escaping by condensing them back to liquids.

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15
Q

What should be included in the drawing of a reflux set up. And what should not be included.

A

Don’t draw lines between flask and condenser.
•Don’t have top of condenser sealed.
•Condenser must have outer tube for water that is sealed at top and bottom•
Condenser must have two openings for water in and out that are open.

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16
Q

What should be included in the drawing of a reflux set up. And what should not be included. Draw this set up.

A

Don’t draw lines between flask and condenser.
. Need : round bottomed flask with anti bumping granuals
•Don’t have top of condenser sealed.
•Condenser must have outer tube for water that is sealed at top and bottom•
Condenser must have two openings for water in and out that are open. SEE PICTURE.

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17
Q

What two safety measures can be used for a reflux and distilation aparatus.

A

1) Never seal the end of the condenseras the build up of gaspressure could cause the apparatus to explode. This is true of any apparatus where volatile liquids are heated including the distillation set up.
2) Anti-bumping granules are added to the flask in both distillation and reflux to prevent vigorous, uneven boiling by making small bubbles form instead of large bubbles.

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18
Q

Why is it not necassary to consider secondary alcoholes in terms of partial and full oxidation and so why is reflux or distialtion not a choice condition that needs tobe changed.

A

This is as there is only one possible product, a ketone, that cant be oxidised any further under thease conditions. If there is only one product to choose from then there would no need to distil off the products and so reflux is the only choice.

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19
Q

Why is it not necassary to consider secondary alcoholes in terms of partial and full oxidation and so why is reflux or distialtion not a choice condition that needs to be changed.

A

This is as there is only one possible product, a ketone, that cant be oxidised any further under thease conditions. If there is only one product to choose from then there would no need to distil off the products and so reflux is the only choice.

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20
Q

Give an equation in word structural and displayed formula for the oxidatuion of propan-2-ol.

A

propan-2-ol into propanone.

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21
Q

What are the conditions reagent/ what is observed for propan-2-ol into propanone heating with potassium dichromate(VI) solution and dilutesulfuric acid under reflux.

A

Reaction: secondary alcohol into ketone Reagent: potassium dichromate(VI) solution anddilutesulfuricacid.Conditions: heat under reflux
Observation: the orange dichromate ion (Cr2O72-) reducesto the green Cr3+ ion as always when this reagent is involved.

22
Q

Why can tertiary alcoholes not be oxidised at all by potasium dichromate.

A

Tertiary alcohols cannot be oxidised at all by potassium dichromate: This is because there is no hydrogen atom bonded to the carbon with the-OH group.

23
Q

What is a dehydaration reaction.

A

Dehydration Reaction: removal of a water molecule from a molecule.

24
Q

Give the conditions for the reaction of alcoholes with dehydrating agents. Also state the role of the catalyst that is used.

A

Reaction: Alcohol into Alkene
Reagents: Concentrated sulfuric or phosphoricacids Conditions: warm (under reflux) Role of reagent:dehydrating agent/catalyst
Type of reaction:acid catalysed elimination

25
Q

Give the conditions for the reaction of alcoholes with dehydrating agents. Also state the role of the catalyst that is used and the type of reaction that this is and the product and reactants in general terms.

A

Reaction: Alcohol into Alkene
Reagents: Concentrated sulfuric or phosphoric acid catalyst
Conditions: warm (under reflux) Role of reagent: dehydrating agent/ catalyst
Type of reaction: acid catalysed elimination.
Hot Concentrated H2SO4/ H3PO4

26
Q

What is a big heads up that a dehydration reaction has occured.

A

If you see anything to do with “Hot conc H2SO4 or H3PO4.

27
Q

What is formed when an alcohol undergoes dehydration / acid catalysed elimination.

A

An Alkene AND WATER

remember the water is lost and so doesnt just disapear.

28
Q

State the dehydrating agent for acid catalysed elimination of an alcohol. What is an alternative that could be used.

A

“Hot conc H2SO4 or H3PO4.

29
Q

State the dehydrating agent for acid catalysed elimination of an alcohol. What is an alternative that could be used.

A

“Hot conc H2SO4 or H3PO4.

Aluminium oxide granuals.

30
Q

What types of alcohols would produce isometric products from dehydration and state the 2 possible isomers from bunanol undergoing acid catalysed elimaination (dehydration).

A

Only secondary and tertiary alcoholes would produce position isomers.
But-2-ene and but-1-ene are both possible isomers. But-2-ene would then produce a further isomer since it will exibit geometrical isomerism due to the double bond.
So you have 3 possible products in total:
but-1-ene , Z-but-2-ene , E-but-2-ene.

31
Q

What types of alcohols would produce isometric products from dehydration and state the 2 possible isomers from bunan-2-ol undergoing acid catalysed elimaination (dehydration).

A

Only secondary and tertiary alcoholes would produce position isomers.
But-2-ene and but-1-ene are both possible isomers. But-2-ene would then produce a further isomer since it will exibit geometrical isomerism due to the double bond.
So you have 3 POSSIBLE PRODUCTS in total:
but-1-ene , Z-but-2-ene , E-but-2-ene.

32
Q

Draw a mechanism for the dehydration of butan-2-ol and state the major product and how you know that this is the major product. Give the structural formula for this reaction and the temperature.

A

See picture for the mechanism of dehydration.
More but-2-ene would be formed as the major product. This is as you need to understand thar dehydration is just an eleimination reaction , you dont actually need to explain why there would be more but-2-ene.
CH3CH2CH2OH INTO CH2=CHCH3+ H2O
600K

33
Q

Give the 3 steps to a mechanism of dehydrating an alcohol and all the subleties to consider.

A

The H+ from the acid catalyst Accepts 2e- from the lone pair on the oxygen.
The oxygen now has a positive charge and so the oxygen takes an e- from the carbon it is bonded to.
To make up for this the neiboring caabon will “swing in” (transfer) its electrons from its C-H bond to form a C=C with the the carbon that originally lost its electrons to neutralise the O.

SUBTLETIES
During the neutralisation step H2O molocule is lost.
There will also be a H+ lost during the formation of the doube bond.
It may feel intuitive to draw the arrow from the H+
IT IS THE O: that the electrons move from so the arrow needs to go FROM O: to the H+ not the other way around.

34
Q

In a dehydration reaction where does the H+ come from and what does it act like in a normal elimination reaction.

A

It comes from whatever acid is used: HOT CONC H2SO4 or H3PO4.
Acts like an electrophile

35
Q

What condition must be met in order for an alcohol to be dehydrated and why cant a ketone be further oxidsed.

A

An alcohol must have a hydrogen atom on the carbon nect to the -OH so that it can “swing in” the e- from the C-H and form the C=C.

36
Q

What is the significance of dehydration in industry.

A

Producing alkenes from alcohols provides a possible route to polymers without using monomers derived from oil.

37
Q

Give an equatuion in words structural and skeletal formula for the oxidation propan-1-ol with exess dichromate(VI) when heated
under reflux. What are significant about such reactions.

A

They all require 2[O] rather than [O] since there is two partial oxidations taking place. Twice as much oxidising agent is used compared to oxidising a primary alcohol to its corrosponding aldehyde.
Reactions
- propan-1-ol into propanoic acid.
- CH3CH2CH2OH + 2[O] INTO CH3CH2COOH + H2O
All still require H2O so the 2[O] will balance.
See picture.

38
Q

What conditions and reagents are used for the full oxidation of primary alcoholes. Hint - consider the different things that must be done together.

A

Reagent: potassium dichromate(VI) solution and dilute sulfuric acid
Conditions: use an excess of dichromate, and heatunder reflux: (distil off product after the reactionhas finished).
Since it is is reflux, a mixture will be left in the flask (consisting of which will be needed to be distiled off in the distilation aparatus that is used for partial oxidation of primary alcoholes.

39
Q

Draw a mechanism for the hydration of ethene and give the teqnical name of the mecanism that you may need to give in an exam. State the catalyst that produces the H+.

A

SEE PICTURE FOR MECHANISM.
It is an acid catalysed addition mechanism.
H+ comes from concentrated H3PO4 catalyst.

40
Q

If in doubt weather to give concentrated H2SO4 or HPO3 which should you go for.

A

Go for H3PO4 since it is a possible catalyst in both the a acid catalysed elimination and acid catalysed addition reaction (hydration or dehydration) or ethanol / ethene.

41
Q

What are the two ways that one could produce ethanol.

A

Fermentation or industrial hydration of ethene.

42
Q

Give a word and structural formula equation for the production of ethanol by fermentation.

A

Glucose INTO ethanol + carbon dioxide.

C6H12O6 INTO 2CH3CH2OH + 2 CO2.

43
Q

What are the ESSENTIAL conditions you should give in an exam for the fermentation of glucose.

A

Go to conditions should be:

1) Yeast ( to provide enzyme catalysts ).
2) Temperatures of 30-40 degrees.

Other possibility if other two not available for any reason is anerobic conditions so that the ethanol doesn’t get oxidised to ethanoic acid.

44
Q

Explain all of the conditions that are Essential for the production of ethanol by way of Fermentation.

A

The optimum temperaturefor fermentation is around 38oC . At lower temperatures the reaction is too slow. At higher temperatures the yeast dies and the enzymes denature. Fermentation is done in an absence of air because the presence of air can cause extra reactions to occur. It oxidises the ethanol produced to ethanoic acid (vinegar).

45
Q

Give the advantages and disadvantages of producing ethanol by fermentation.

A

Advantages: - sugar is a renewable resource (MAIN ADVANTAGE TO LEARN) since crops grow back anualy.
-production uses low level technology / cheap equipment.
Disadvantages : -BATCH PROCESS which is SLOW and gives high production costs
- ethanol made is not pure and needs purifying by fractional distillation.
depletes land used for growing food crops (examiners love this one).

46
Q

Give the essential conditions for the indutrial formation of ethanol from ethene.

What is the technical name for this.

A

Essential Conditions : high temperature of 300°C
high pressure of 70 atm strong acidic catalyst of conc H3PO4.

Hydration (addition of water to a molecule)

47
Q

Give a reaction , in structural formula , for the industrial production of ethene by reacting with steam and state where the reagent comes from.

A

CH2=CH2 gas + H20 gas into CH3CH2OH luiqid. H3PO4 catalyst above the reaction.
The ethene reagent comes from the cracking of fractions of crude oil.

48
Q

Give the advantages and disadvantages of produing ethanol by hydration of ethene (acid catalysed addition mechanism) of ethene rather than by fermentation.

A

Advantages:•
faster reaction•
purer product•
continuous process (which means cheaper man power)
Disadvantages:
•high technology equipment needed (expensive initial costs)• ETHENE IS NON RENEWABLE (will become more expensive when raw materials run out )
•highenergy costs for pumping to produce highpressures

49
Q

Define the term biofuel and define the term carbon neutural.

A

A biofuel is a fuel produced from plants.
The term carbon neutral refers to “an activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere.

50
Q

State the type of fule ethanol produced from fermentation is and give the argument for why this is the case. Then also give a counter argument for why in reality this may not be the case.

A

Ethanol produced from fermentation is a biofuel. It can be argued that ethanol produced from this method is classed as carbon–neutral because any carbon dioxide given off when the biofuel is burnt would have been extracted from the air by photosynthesis when the plant grew. There would be no net CO2 emission into the atmosphere.
However: This does not take into account any energy needed to irrigate plants, fractionally distil the ethanol from the reaction mixture or process the fuel. If the energy for these processes comes from fossil fuels then the ethanol produced is not carbon neutral.

51
Q

Write , with the aid of equations , why theoreticaly there is no net contribution of CO2 to the atmosphere when ethanol is produced via fermentation , label all of the steps in your answer. Write in brief terms something about this equation that could potentially catch you out.

A

Removal of CO2 by photosynthesis:
6CO2+ 6H2O INTO C6H12O6+ 6O2
6CO2 molecules are removed from the atmosphere when the plants grow by photosynthesis to produce one molecule of glucose.
Production of CO2 by fermentation and combustion:
C6H12O6 INTO 2CH3CH2OH+2 CO2
2CH3CH2OH+ 6O2 INTO 4CO2+ 6H2O
The fermentation process will balance nicely with the products having 2 moles each.
YOU NEED TO BALANCE YOUR COMBUSTION EQUTION ALL AROUND MAKING 4 MOLES OF CO2 - just do this even if it doesnt follow usual combustion balancing rules.

52
Q

When would high resolution mass spectrometry be used.

A

When compounds APPEAR to have a similar Mr to the nearest whole number,

chemistry a- level (18 decks)

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