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Organic chemistry > Alcohols > Flashcards

Alcohols Flashcards

(39 cards)

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1
Q

Describe bond angles and
the shape of alcohols

A

HCH bonds and the CCO bonds are 109.5 degrees, tetrehederal shape
4bp

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2
Q

Describe boiling points of alcohols

A

High boiling points due to their ability in forming hydrogen bonds between alcohol molecules, this means they have a higher bp than alkanes of their same molecular mass

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3
Q

What is a primary alcohol?

A

Alcohols where only one carbon is attached to the carbon adjoining the oxygen molecule in the OH e.g Propan-1-ol

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4
Q

What is a secondary alcohol?

A

Alcohols where two carbon atoms are attached to the carbon that adjoins the oxygen molecule in the OH e.g Propan-2-ol

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5
Q

What is a tertiary alcohol?

A

Alcohols where 3 carbon atoms are attached to the carbon that adjoins the oxygen molecule in the OH e.g Methylpropan-2-ol

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6
Q

Describe the solubility of alcohols

A

-OH group in alcohols means that hydrogen bonding can occur with water molecules, however the rest of the chain cannot as it is non polar
- This means alcohols with short hydrocarbon chains are soluble in water as hydrogen bonding predominates, however in long hydrocarbon chains non polar region of the hydrocarbon chain dominates and alcohols become insoluble in water

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7
Q

Give the equation for the production of ethanol using fermentation

A

Glucose= ethanol+ carbon dioxide
C6H12O6= 2CH3CH2OH+ 2CO2

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8
Q

Give the conditions needed for the production of ethanol using fermentation

A

-Yeast
-No air
-Temperatures of around 30 degrees to 40 degrees
- Optimum temp of 38 degrees

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9
Q

Give the optimum temperature used for the production of ethanol using fermentation and explain why

A

38 degrees
Lower temps reaction is too slow
Higher temps yeast dies and enzymes denature

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10
Q

Explain why fermentation of glucose to produce ethanol is done in the absence of air

A

Presence of air can cause extra reactions to occur
Oxidises the ethanol produced to be ethanoic acid

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11
Q

Describe advantages of using fermentation to produce ethanol from glucose

A
  • Sugar is a renewable resource
    -Production uses low level technology so its cheap
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12
Q

Describe how ethanol is produced industrially

A

Uses ethene from the cracking of fractions from distilled crude oil
In a hydration/addition reaction
( addition of a water molecule)

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13
Q

Describe conditions needed for the production of ethanol industrially

A

High temp of 300 degrees
High pressure of 70 atm
Strong acidic catalyst= conc H3P04

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14
Q

Describe the advantages of producing ethanol industrially

A

-Faster reaction
- Purer product
-Continuous process( cheaper manpower)

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15
Q

Describe the disadvantages of producing ethanol industrially

A

High tech equipment needed( expensive initial costs)
Ethene is a non renewable resource( it becomes more expensive when raw materials run out)
High energy costs for pumping to produce high pressures

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16
Q

Describe the disadvantages of producing ethanol by fermentation

Study These Flashcards
A

Batch process which is slow and gives high production costs
Ethanol is made impure which means it needs purifying by fractional distillation
-Depletes land used for food crops

17
Q

What is a biofuel

Study These Flashcards
A

A fuel produced from plants

18
Q

What does carbon neural mean

Study These Flashcards
A

An activity that has no net annual carbon emmisions into the atmosphere

19
Q

Why may people believe that ethanol produced from fermentation is classed as carbon neural?

Study These Flashcards
A

Because any carbon dioxide given off when the biofuel is burned would of been extracted from the air by photosynthesis when the plant grew, no net CO2 emmison into the atmosphere

20
Q

Give the equations that show there is no net contribution to CO2

Study These Flashcards
A

Removal of CO2 by photosynthesis
6CO2+ 6H2O= C6H12O6 + 6O2
6 CO2 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 = 2CH3CH2OH + 2 CO2
2CH3CH2OH + 6O2 = 4 CO2 + 6 H2O
When 1 molecule of glucose is fermented 2 molecules of CO2
is emitted. The two ethanol molecules produced will then produce 4 molecules of CO2 when they are combusted.
For every 6 CO2 molecules emitted 6CO2 molecules are absorbed

21
Q

Why is the statement that ethanol produced from fermentation is carbon neural invalid?

Study These Flashcards
A
  • Doesnt take into account the fact that energy is needed to irrigate plants
    -Energy is also needed to fractionally distill the ethanol from the reaction mixture or process the fuel
  • If the energy needed for this process comes from fossil fuels
22
Q

Details of oxidation of primary alcohols ( partial)

Study These Flashcards
A

Partial oxidation of primary alcohols forms aldehydes
Reagent used is potassium dichromate(VI) solution and dilute H2SO4
Conditions needed are a limited amount of the dichromate, warm gently and distill out the aldehyde as it forms, excess of alcohol is used as it means there isnt enough oxidising agent to carry out the second stage

23
Q

Give the structural formula equation of propan-1-ol being oxidised to propanal ( partial oxidation of P alcohols)

Study These Flashcards
A

CH3CH2CH2OH + (O)= CH3CH2CHO+ H2O
Propan-1-ol is being oxidised to the aldehyde propanal and water is produced
Always condense an aldehyde with the end being CHO instead of COH

24
Q

Describe the observation seen when primary or secondary alcohols are oxidised

Study These Flashcards
A

The orange dichromate ion (Cr2O7)2- in the reagent potassium dichromate (VI) is reduced to the green Cr3+ ion ( chromium III ion)
Colour change - Orange to green observation
Electron half equation- Cr2O72- + 14H+ +6e- = 2Cr3 + 7H2O

25
Which method is used to obtain an aldehyde from partial oxidation of primary alcohol? e.g ethanol
Distillation -Mixture of the ethanol, dilute sulfuric acid and the potassium dichromate is heated gently in a round bottomed flask - Reciever is cooled in ice to reduce evaporation of the product (improve the yield of the distillate) - Ethanal vapourises as soon as it is formed and distills off to stop it from being oxidised further to ethanoic acid - Unreacted ethanol remains in the flask - An electric heater is used to heat the bottom of the flask ( heat the organic chemicals) because these are usually highly flammable and can set on fire with a naked flame -Thermometer bulb is placed at the T junction connecting to the condenser to measure the correct boiling point
26
Give details about the full oxidation of primary alcohols
Reaction- primary alcohols are fully oxidised to form carboxylic acids Reagent- Potassium dichromate(VI) solution and dilute sulfuric acid Conditions- use an excess of dichromate and heat under reflux ( distill off product until the reaction has been finished) Make sure the aldehyde stays in the mixture when it is formed as a half way product
27
Give the structural formula equation to show propan-1-ol being fully oxidised
CH3CH2CH2OH+ 2(O) = CH3CH2COOH + H2O Propan-1-ol is oxidised by potassium dichromate(VI) solution to form propanoic acid( carboxylic acid) and a water molecule is formed
28
Describe the method used for fully oxidising primary alcohols to form a carboxylic acid?
Reflux is used as we are heating organic mixtures for long periods of time - The condenser prevents organic vapours from escaping by condensing them back to liquids - End of condenser is never sealed as the build up of gas pressure could cause the apparatus to explode, true of any experiment where volatile liquids are heated including the distillation set up - Antibumping granules are added to the flask in both distillation and reflux to prevent vigarous, uneven bubbling by making small bubbles form instead of large bubbles
29
Give details for the oxidation of secondary alcohols
Reaction is a secondary alcohol is fully oxidised to form a ketone Reagent- Potassium dichromate (VI) solution and dilute sulfuric acid -Conditions ( heat under reflux)
30
Naming ketones
-They end in -one -When ketones have 5Cs in a chain or more, it needs a number to show the position of the double bond e.g pentan- 2 -one
31
Why cant tertiary alcohols be oxidised by the potassium dichromate (VI)?
No hydrogen atom bonded to the carbon with the -OH group, so there is no hydrogen attached to the carbon for the oxidising agent to remove
32
Why are chemical tests used to distinguish between aldehydes and ketones?
Aldehydes can be oxidised to form carboxylic acids However ketones dont get oxidised any further
33
Describe the reaction and the observation when tollens reagent is used to distinguish between aldehydes and ketones
Aldehydes only are oxidised by Tollens reagent into a carboxylic acid. The silver (I) ions are reduced to silver atoms Observations- with aldehydes a silver mirror is formed coating the inside of the test tube Ketones result in no visible change
34
Describe the conditions of the reaction using tollens reagent to distinguish between aldehydes and ketones with equation
Tollens reagent is formed by mixing aqeous ammonia and silver nitrate, active substance is a complex ion called (Ag(NH3)2)+ Need to heat gently Equation- CH3CHO+ 2Ag+ H2O= CH3COOH + 2Ag 2H+ Aldehyde gets oxidised by the reagent to form silver atoms
35
Describe the observation reaction and equatons of using fehlings solution to distinguish between aldehydes and ketones
Aldehydes only are oxidised by the fehlings solution into a carboxylic acid, the copper(II) ions are reduced to copper(I) oxide Observation shows that when an aldehyde is present, the blue CU2+ ions in the solution change to a red precipitate of CU2O Ketones dont react CH3CHO+ 2Cu2+ 2H2O= CH3COOH + Cu2O+ 4H+
36
Describe method of using tollens solution
To carry out the test, you add a few drops of the aldehyde or ketone to the freshly prepared reagent, and warm gently in a hot water bath for a few minutes.
37
Describe the reagent and conditions used to form alkenes from alcohols ( acid catalysed elimination)
Reagent- conc sulfuric or phosphoric acid Conditions-warm ( under reflux) Conc sulfuric or phosphoric acid are used as dehydrating agents/ catalysts
38
What is the purpose of of producing alkenes from alcohols?
Provides a possible route to polymers without using monomers derived from crude oil
39
What is a dehydration/elimination reaction?
Removal of a water molecule is dehydration( elimination reactions in alcohols are always dehydration reactions) Elimination in general is when a small molecule is removed from a large molecule

Organic chemistry (9 decks)

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