Alcohols Flashcards
Define alcohol
Alcohol’s are organic compounds which are characterised by the presence of one or more hydroxyl groups (−OH) that are attached to the carbon atom in an alkyl group or hydrocarbon chain.
Alcohols can be classified as one of three groups based on the number of carbons attached to the carbon with the hydroxyl group. What are the groups called?
Primary, secondary or tertiary
How many carbons does primary alcohols have attached to the carbon with the hydroxyl group?
One carbon
How many carbons does a secondary alcohol have attached to the carbon atom with the hydroxyl group?
2 Carbons
How many carbons does a tertiary alcohol have attached to the carbon atom with the hydroxyl group?
3 carbons
Why did ethanol production change from fermentation to an alternative industrial process?
Fermentation is too slow so using steam and ethane is easier.
What’s the general formula for other alcohols produce from steam and an appropriate alkene?
CnH2n + H2O —> CnH2n+1OH
Draw the overall equation to make ethanol from ethene.
C2H4(g) + H20 —> C2H5OH (g)
enthalpy change = -45kJmol-1
What is the reaction called called that converts Alkenes from alcohols with the addition of water?
Hydration
What is the theoretical atom economy of the reaction converting ethene to ethanol?
100%
Define fermentation
The biological process in which glucose is converted into ethanol and carbon dioxide
What enzyme is used for the fermentation of ethanol to make glucose
Zymase, found in yeast
What’s the optimum temperature for zymase?
37-40 degrees Celsius
What is the formula for the reaction between ethanol glucose and carbon dioxide?
Glucose —> Ethanol + Carbon Dioxide
C6H12O6(aq)—> 2CH3CH2OH(aq) +2CO2(g)
What are the conditions for the fermentation of glucose to make ethanol?
The absence of oxygen, the presence of yeast and sugar ( glucose ) solution and a temperature of 37-40 degrees Celsius
What is biofuel?
A biofuel is a fuel made from biomass
Write out the formula of ethanol reacting exothermically with oxygen to produce carbon dioxide and water.
C2H5OH(g) + 3O2(g) — 2CO2(g) + 3H2O(l)
Enthalpy change = -1367kJmol-1
Draw the equations that demonstrate ethanol made by fermentation as being carbon neutral and explain why it is carbon neutral?
Find in camera roll 27th of January
Explanation: Making ethanol by fermentation makes the same amount of carbon dioxide and water as in photosynthesis
Why do the statement that ethanol produced by fermentation is carbon neutral
Because it requires energy that may come from burning fossil fuel power, or in fossil fuel power stations which produces carbon dioxide
Process of producing ethanol fuel involves three stages what are those?
Stage 1: Starches are converted to glucose using enzymes. These digest the starches in a similar way to the enzymes in your digestive system
Stage 2: Fermentation reactions convert glucose into ethanol and carbon dioxide. A mixture of ethanol, water, unteaches glucose and dead yeast cells is obtained
Stage 3: Fractional distillation is used to separate the ethanol. Fractional distillation is used to separate liquids with different boiling points. The boiling point of ethanol is 78 degrees Celsius(dc) and water 100 (dc) By heating the reaction mixture, ethanol can be boiled off at 78(dc) and the vapour condensed and collected
Draw a comparison table of fermentation to produce ethanol and production from ethene and steam
Find on page 300 in text book or in camera roll on 27th of January.
Dilute acidified potassium dichromate (VI) solution can be used as….
An oxidising agent to oxidise alcohols in a reaction to its dilute sulphuric acid added
Products d pens in whether the alcohol is primary, secondary or tertiary alcohol
What type of alcohol is ethanol?
Ethanol is a primary alcohol
What is the product of ethanol oxidation under conditions where the aldehyde is distilled off as it forms?
Ethanal (aldehyde)
Why is the aldehyde distilled off during the oxidation of ethanol?
To prevent further oxidation of the aldehyde to a carboxylic acid.
What happens to ethanol molecules during oxidation to form an aldehyde?
Two hydrogens are removed one from the carbon skeleton and one from the hydroxyl group.
What is the general naming rule for aldehydes?
The names of aldehydes end in “-al,” and the first part of the name is based on the alkyl group present.
What is the aldehyde formed by the oxidation of ethanol?
Ethanal
What is the simplified equation for the oxidation of ethanol to ethanal?
CH3CH2OH + [O] —> CH3CHO + H2O
What is the role of acidified potassium dichromate(VI) in the oxidation of ethanol?
It acts as the oxidising agent.
What happens when ethanol is oxidised using excess acidified potassium dichromate(VI) under reflux?
A carboxylic acid (ethanoic acid) is produced.
What is the simplified equation for the oxidation of ethanol to ethanoic acid?
CH3CH2OH + 2[O] —> CH3COOH + H2O
What additional atom is gained when an aldehyde is oxidised to a carboxylic acid?
One oxygen atom is gained.
What is the carboxylic acid formed by the complete oxidation of ethanol?
Ethanoic acid.
What is the elimination reaction of alcohols commonly called?
Dehydration, because water is lost from the molecule.
What happens to bonds in the dehydration of alcohols?
The C–O bond in the alcohol breaks, and one hydrogen atom is lost from the carbon chain.
Write the reaction for the dehydration of ethanol.
Answer on page 307 or camera on date 27 January
What are the required conditions for the dehydration of alcohols?
Heating with a suitable catalyst, such as concentrated sulfuric acid (H₂SO₄) or phosphoric acid (H₃PO₄).
What role does sulfuric acid play in the dehydration reaction of alcohols?
Sulfuric acid acts as a catalyst and is chemically recovered unchanged at the end.
What happens to ethanol in the presence of sulfuric acid during the dehydration process?
A proton (H⁺) is transferred from sulfuric acid to ethanol, initiating a series of electron rearrangements that lead to the formation of ethene and water.
What is the role of the hydrogen sulfate ion (HSO₄⁻) in the reaction?
It accepts a proton (H⁺), reforming sulfuric acid and completing the catalytic cycle.
Describe the laboratory method to dehydrate ethanol to ethene.
Ethanol vapor is passed over a hot catalyst, such as pumice stone or aluminum oxide, and the ethene produced is collected over water.
What is the product of ethanol dehydration?
Ethene (C₂H₄) gas and water (H₂O).
Why is a catalyst like pumice stone or aluminum oxide used in the laboratory method?
To provide a surface for the reaction and help the dehydration process occur.
What type of process is fermentation in ethanol production?
Fermentation is a batch process, meaning the reaction vessels must be emptied, cleaned, and restocked after each batch.
What type of process is ethanol production from ethene and steam?
It is a continuous process, where ethene and steam are continuously fed over a catalyst, and unreacted reactants are recycled. Continuous processes are generally more cost-effective than batch processes.
How does the reaction rate of fermentation compare to that of production from ethene and steam?
The reaction in fermentation is slow, while the reaction in production from ethene and steam is rapid.
What are the temperature and pressure conditions for fermentation?
Fermentation occurs at a relatively low temperature and atmospheric pressure.
What are the temperature and pressure conditions for ethanol production from ethene and steam?
The process requires a high temperature and pressure, which makes it expensive to maintain.
How labor-intensive is fermentation compared to production from ethene and steam?
Fermentation is labor-intensive, from growing the crops to purifying the final ethanol product. In contrast, ethanol production from ethene and steam requires fewer workers, as it is largely automated with low labor requirements.
Why does fermentation require fractional distillation?
Fractional distillation is needed to purify the ethanol product in fermentation, which uses additional energy.
Does ethanol produced from ethene and steam require purification?
No, the ethanol produced is between 98-99% pure, meaning it does not require purification for most purposes.
What type of resources does fermentation use?
Fermentation uses renewable resources, as it relies on biomass such as sugarcane or corn.
What type of resources does ethanol production from ethene and steam use?
Ethene is produced from crude oil, which is a finite resource, making this method dependent on non-renewable resources.
How does land use differ between fermentation and production from ethene and steam?
Fermentation requires land for growing biomass, which could also be used for food production. In contrast, ethanol production from ethene and steam does not require farming land.
