Alcohols Flashcards
What is the general formula for an alcohol
Cn H2n+1 OH
What is the Symbol equation for Hydration(ethene is used as an example)
(done in strcutural formula)
CH2=CH2 (g) + H2O (g)→ CH3CH2OH (l)
A hydroxyl group (OH−) attaches to one carbon of the double bond, and a proton (H+) adds to the other. The reaction is highly exothermic
What are the conditions required for Hydration(3)
- High temperature
- High pressure
- Strong acidic catalyst of Phosphoric acid
(represented as H+)
What are the disadvantages of Hydration(3)
- High technology equipment required which costs money
- Ethene is a non renewable resource so will runn out one day
- High energy costs for pumping to produce high pressures
Advanages of HYDRATION (3)
- Faster reaction
- Purer product
- Continuous process
What regeant is required for hydration
Ethene
What is the Balanced symbol equatin of Fermentation
C6H12O6 (aq)–> 2C2H5OH(aq) + 2CO2(g)
What are the conditions required for fermentation
- Yeast
- Anaerobic conditions -no oxygen- (because oxygen could cause extra reactions- it oxidises the ethanol produced to ethanoic acid (vinegar)
- Temp of 30-40 (38 is optimum temp)
What happens if the temperature is too high or too low in fermnetation
Too low: Reaction will be very slow
Too high:Yeast dies and enzymes denature
Advantages of fermentation
- Sugar is a renewable resource
- Production uses low level technology
- Cheap equipment
Disadvantages of fermentation
- Batch process which is slow and gives high production costs
- Ethanol made is impure and needs purifying by fractional distillation
- Depletes land as crops need land
What is the Dehydration of ethanol
The removal of water from ethanol also known as an elimination reaction
What are the steps in the dehydration of ethanol
- Draw arrow from the lone pairs on the O in the alcohol to the H+(Catalyst)
- H gets added to the hydrocl group which forms RC-O-H2 (O becomes positive)
- A H from the next carbon over gives an electron to the C (draw arrow from H to the C
- Draw arrow from C to the O
- You get your product (ooverall reation =Alkene + water + H+
What is a biofule
A biofuel is a fuel produced from plants
Define carbon neutral
An activity that has no net annual carbon (greenhouse gas) emissions to the atmosphere”
Why is ethanol 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.
Equations to show no net contribution to CO2
6 CO2 + 6 H2O –> C6H12O6 + 6 O2 -6 CO2 molecules are removed from the atmosphere when the plants grow by photosynthesis to produce one molecule of glucose.
C6H12O6 –> 2 CH3CH2OH + 2 CO2 -When 1 molecule of glucose is fermented 2 molecules of CO2 is emitted.
2 CH3CH2OH + 6O2 –> 4 CO2 + 6 H2O -The two ethanol molecules produced will then produce 4 molecules of CO2 when they are combusted.
Overall for every 6 molecules of CO2 absorbed, 6 molecules of CO2 are emitted. There is no net contribution of CO2 to the atmosphere.
What are the conditions, Reagents Role of reagent and type of reaction for the reaction: Alcohol —> Alkene
Reagents: Conc sulfuric acid or phosphoric acid
Conditions: Warm under reflux
Role of reagents: Dehydrating agent/Catalyst
Type of reaction: Acid catalysed elimination
What is an example of the products given out when the double bond forms between different carbon atoms in secondary and tertiary alcohols
For example Butan 2 ol can give you But 1 ene and But 2 ene which can also exist as E-Z isomers
Fact
Producing alkenes from alcohols provides a possible route to polymers without using monomers derived from oil
What are the conditions, Reagents, Role of reagent and type of reaction for the oxidation of secondary alcohols
Reaction: Secondary alcohol —>Ketone
Reagent: potassium dichromate solution and dilute sulfuric acid
Conditions: heat under reflux
Naming for ketone
When ketones have 5C’sor more in a chain then it needs a number to show the position of the double bond. E.g. pentan-2-one
Word equation for how you get a ketone
And what is the observation
Propan-2-ol + [O] —> Propanone(CH3C=OCH3) +H2O
Observation: the orange dichromate ion (Cr2O7^2-) reduces to the green Cr 3+ ion
There is no further oxidation of the ketone under these conditions.
Can tertiary alcohols be oxidised?
Tertiary alcohols cannot be oxidised at all. This is because there is no hydrogen atom bonded to the carbon with the -OH group.
How do you distinguish between Aldehydes and Ketones
- Aldehydes can be further oxidised to carboxylic acids whereas ketones cannot be further oxidised.
- This is the chemical basis for two tests that are commonly used to distinguish between aldehydes and ketones.
What are the two reagents used when testing whether an alcohol is a ketone or an aldehyde
Reagent: Tollens’ reagent formed by mixing
aqueous ammonia and silver nitrate. The
active substance is the complex ion of
[Ag(NH3)2]+
Reagent: Fehling’s solution containing blue Cu 2+ ions.
What are the conditions required for both the reagents used when testing for an aldehyde or ketone
Conditions: heat gently
What are the observations for tollens reagent
Observation: with aldehydes, a silver mirror
forms coating the inside of the test tube.
Ketones result in no visible change
CH3CHO + 2Ag+ + H2O —-> CH3COOH + 2Ag + 2H+
What are the observations for Fehlings solution
Observation: Aldehydes :Blue Cu 2+ ions in
solution change to a red precipitate of Cu2O.
Ketones do not react
CH3CHO + 2Cu2+ + 2H2O —> CH3COOH + Cu2O + 4H+
How can carboxylic acids be tested
By the addition of sodium carbonate. It will fizz and produce carbon dioxide.
What are the conditions and Reagents for the Full oxidation of primary alcohols
Conditions: Use an excess of dichromate and heat under reflux (Distill of product after the reaction has finished
Reagent: Potassium dichromate (VI) solution and dilute sulfuric acid
Reaction:Primary alcohol–>Carboxylic acid
Strcutural formula for propan-1-ol to propanoic acid
CH3CH2CH2OH + 2[O] –> CH3CH2COOH + H2O
What is the observation for carboxylic acids
- Orange to green
- The orange dichromate ion (Cr2O7^2-) reduces to the green Cr 3+
- Sodium carbonate–> fizzing and produces CO2
When is reflux used
Reflux is used when heating organic reaction mixtures for long periods. The condenser prevents organic vapours from escaping by condensing them back to liquids.
What should you never do in reflux
Never seal the end of the condenser as the build up of gas pressure could cause the apparatus to explode. This is true of any
apparatus where volatile liquids are heated including the distillation set up.
Why are antibumping granules used
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.
What is potassium dichromate
Potassium dichromate K2Cr2O7 is an oxidising agent that causes alcohols to oxidise.
What are the conditions and Reagents for the partial oxidation of primary alcohols
Partial Oxidation of Primary Alcohols
Reaction: primary alcohol –> 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:
Naming aldehyde
- An aldehyde’s name ends in –al
- It always has the C=O bond on the first carbon of the chain so it does not need a number in its name
Give the oxidation reaction for propan-1-ol —-> propanal
CH3CH2CH2OH + [O] –> CH3CH2CHO + H2O
When is distillation used
In general used as separation technique to separate an organic product from its reacting mixture. In order to maximise yield collected, only collect the distillate
at the approximate boiling point of the desired aldehyde and not higher.
Why is water filled from the bottom in a Liebig condenser
- To go against gravity
- This allows more efficient cooling and prevents back flow of water.
Naming alcohols
These have the ending -ol and if necessary the position number for the OH group is added between the name stem and the –ol
If the compound has an –OH group in addition to other functional groups that need a suffix ending then the OH can be named with the prefix hydroxy-):
If there are two or more -OH groups then di, tri are used. Add the ‘e’ on to the stem name though e.g. ethane-1,2-diol propane-1,2,3-triol
What is a tertitary alcohol
Tertiary alcohols are alcohols where 3 carbon are attached to the carbon adjoining the oxygen.
Alcohol solubility
Smaller alcohols can dissolve in water because they can form hydrogen bonds to water molecules.
Boiling points in alcohols
The alcohols have relatively low volatility and high boiling points due to their ability to form hydrogen bond between alcohol molecules.
Bond angles in alcohols
All the H-C-H bonds and C- C-O are 109.5o
(tetrahedral shape), because there are 4 bonding pairs of electrons repelling to a position of minimum repulsion.
The H-O- C bond is 104.5 (bent line shape), because there are 2 bonding pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion. Lone pairs repel more than bonding pairs so the bond angle is reduced.
