Alcohols Flashcards
What is the functional group of alcohols?
The hydroxyl (oh) group
What is the suffix and prefix for alcohols?
Suffix- ol
Prefix- hydroxy
What defines primary alcohols?
They have one carbon attached to the carbon with the hydroxyl group
What defines secondary alcohols?
They have two carbons attached to the carbon atom with the hydroxyl group
What defines tertiary alcohols?
They have three carbons attached to the carbon with the hydroxyl group. This means they will have a methyl group
What is the general equation in the production of alcohols from steam and the appropriate alkene and give the equation for ethene and steam
CnH2n +H2O -> CnH2n+1OH
C2H4 +H2O -> C2H5OH
What is the reaction of ethene and steam called?
A hydration reaction because the reaction involves the addition of water
What are the conditions used in the hydration reaction?
A temperature of 600 K, a pressure of 6000-7000 kPa and a concentrated phosphoric (V) acid catalyst held in silica pellets
How do you achieve an overall 95 % conversion rate in the conversion of ethene to ethanol?
By removing the ethanol and recycling the unredacted ethene
What is the biological process in which glucose is converted into ethanol and carbon dioxide called?
Fermentation
Fermentation reactions are catalysed by enzymes called zymase which are found in yeast. What are the conditions for this process?
- the absence of oxygen (it is anaerobic)
- The presence of yeast and sugar (glucose) solution
- a temperature of 37-40 °c
What is a biofuel and what happens when it’s burnt?
It’s a fuel made from biomass. The plants that make up the biomass used carbon dioxide from the atmosphere to make sugar in photosynthesis. When they are burnt carbon dioxide is produced and returned to the atmosphere
What is an equation for the fermentation reaction?
C6H12O6 -> 2CH3CH2OH +2CO2
Glucose ethanol carbon dioxide
What is the equation for the combustion of ethanol?
C2H5OH + 3O2 -> 2CO2 + 3H2O
Why can it be said that the ethanol made by fermentation is a carbon neutral fuel?
Because making ethanol by fermenting a solution of glucose and the combusting the ethanol produces the same amounts of carbon dioxide and water as are used in photosynthesis
Why would it be said that the statement that ethanol produced by fermentation is a carbon neutral fuel is not valid?
Because it requires energy to obtain ethanol from the solution produced by fermentation. Power is also needed for various other operations in the manufacturing process. This energy may come from burning fossil fuels which also produces carbon dioxide
Give examples of the crops that can be used to provide sugars and starches for use in fermentation
Sugar cane, wheat or corn
Give the three stages of the process to produce ethanol fuel
1) starches are converted to glucose using enzymes
2) fermentation reactions convert glucose into ethanol and carbon dioxide. A mixture of ethanol, water, unreacted glucose and dead yeast cells is obtained
3) fractional distillation is used to separate the ethanol. By heating the reaction mixture ethanol can be boiled off at 78°c and the vapour condensed and collected
Compare the economic aspects of fermentation and production from ethene and steam. Give five comparisons
- fermentation is a batch process whereas production from ethene and steam is a continuous process which is more cost-effective as the reactants are recycled.
- fermentation is slow whereas ethene and steam is rapid
- fermentation occurs at a relatively low temperature and atmospheric pressure whereas ethene and steam uses a high temperature and pressure which are expensive to maintain
- fermentation is labour intensive whereas few workers are needed to operate the system in ethene and steam
- in fermentation fractional distillation is needed to purify the product which uses energy whereas in ethene and steam the ethanol produced is between 98 and 99% pure
Give two comparisons of the environmental aspects in fermentation and production from ethene and steam
- fermentation uses renewable resources whereas ethene us produced from crude oil
- in fermentation the land used for growing biomass for fermentation is also needed for food production whereas the production of ethene and steam does not use farming land
What are two examples of alcohol reactions?
Oxidation and elimination
What is the reagent used as an oxidising agent to oxidise alcohols?
Acidified potassium dichromate (VI) solution
What can primary alcohols be oxidised to?
An aldehyde and then further oxidised to a carboxylic acid
What conditions will help to produce an aldehyde from a primary alcohol?
An excess of alcohol is used and the aldehyde is distilled off as it forms
What is the equation to produce ethanal from ethanol?
CH3CH2OH + [O] -> CH3CHO + H2O
What conditions make it more likely that a carboxylic acid will be produced from the oxidation of a primary alcohol?
If an excess of acidified potassium dichromate solution is used and the reaction mixture is heated under reflux
What happens when a secondary alcohol is refluxrd with acidified potassium dichromate?
Two hydrogens are removed and a ketone if produced. Water is the other product of the reaction.
Draw the difference between the functional group of a ketone and aldehyde
Aldehyde:
H
|
C = O
|
R
Ketone:
R
|
C=O
|
R1What is the equation for the production of ethanoic acid from a primary alcohol?
CH3CH2OH + 2[O] -> CH3COOH + H20
Why cant tertiary alcohols be oxidised?
Because they have no hydrogens bonded to the carbon that carries the hydroxyl group that can be removed in the oxidation process.
Why is a ketone more difficult to oxidise than an aldehyde?
Because the carbon in the C=O o d in a ketone is bonded to two other carbons whereas in a aldehyde it is just one.
What are the two reagents that may be used to distinguish between an aldehyde and a ketone and what do they both give positive results for?
Tollen’s reagent and Fehlings solution
They both give positive results for aldehydes
Tollen’s reagent is prepared by mixing aqueous ammonia NH3 and silver nitrate solution AgNO3. What does the resulting solution contain?
Diamine silver ions [Ag(NH3)2] +
What would you observe when Tollens reagent is warmed with an aldehyde and why?
Silver atoms coat the inside of the test tube producing a silver mirror. The silver mirror forms because silver ions are reduced to silver atoms by the aldehyde which is oxidised to a carboxylic acid.
What does Fehlings solution contain and what to the act as?
Deep blue copper (II) ions dissolved in dilute ammonia.
The complex copper (II) ions act as a weak oxidising agent and oxidised an aldehyde to give a carboxylic acid.
What would you observe when an aldehyde is heated with Fehlings solution?
A brick red precipitate forming when copper (II) ions are reduced. This is because they are reduced to copper oxide
How can you identify whether an alcohol is primary and secondary or tertiary?
When primary and secondary alcohols are oxidised the oxidising agent is reduced and when potassium dichromate solution is the oxidising agent the colour changes from orange to green because dichromate (VI) ions (orange) are reduced to chromium (III) ions (green)
In distillation why are anti bumping granules used?
They help the contents to boil smoothly as bumping occurs when larger gas bubbles collect in the flask and then rise to the surface causing the distillation mixture to rise up in the apparatus
Why is the distillation mixture (flask) heated in a water bath
To reduce exposure to naked flame so less of a fire hazard
What do elimination reactions involve?
The loss of water from an alcohol to form an alkene
What is another word for an elimination reaction and why?
A dehydration because water is lost from the molecule.
What happens during an elimination reaction?
The C-O bond in the alcohol breaks and one hydrogen atom is lost from the carbon chain
What are the conditions for an elimination reaction?
Heating with a suitable catalyst such as concentrated sulfuric acid or concentrated phosphoric acid
Draw the mechanism for elimination reaction of alcohols
Picture on camera roll
Why can the sulfuric acid in an elimination reaction be said to be a catalyst?
The hydrogen sulfate ion HSO4 - accepts a hydrogen ion (H +) reforming sulfuric acid so it is unchanged at the end
In the laboratory what reaction can the dehydration of ethanol be done to produce ethene?
Dehydration of ethanol over a
Hot pumice stone or aluminium oxide
