AS - Alcohols Flashcards
How are alcohols produced industrially?
By hydration of alkenes using steam in the presence if an acid catalyst.
How is ethanol produced industrially?
By the fermentation of glucose.
What is the general formula of an alcohol? What is this often shortened to?
CnH2n+1OH.
ROH.
What is the functional group in an alcohol? Name this group.
-OH, the hydroxyl group.
How are alcohols classified?
Either as primary, secondary or tertiary depending on how many other groups (R) are bond to the carbon that had the hydroxyl group.
Define a primary alcohol.
The carbon with the -OH group had one R group and two hydrogen atoms attached.
What classification is methanol considered as?
Primary.
Define a secondary alcohol.
The -OH group is attached to a carbon with two R groups and one hydrogen atom.
Define a tertiary alcohol.
Three R groups are attached to the carbon bonded to the -OH group.
Outline the mechanism for the formation of an alcohol by the reaction of an alkene with steam in the presence of an acid catalyst.
- A pair of electrons from the double bond in the alkene bonds to an H+ ion if the acid catalyst.
- A lone pair of electrons from a water molecule bonds to the resulting carbocation.
- The water loses an H+ ion forming an alcohol and H+.
What conditions are used in the production of ethanol from the hydration of ethene?
300 degrees Celsius, pressure of 60 atm and the catalyst is solid phosphoric (V) acid.
What is a biofuel?
A fuel thats made from renewable biological material that’s recently died.
Is fermentation an exothermic or endothermic process?
Exothermic.
Outline the conditions required for the fermentation of glucose to form ethanol.
- Carried out by yeast.
- Anaerobic conditions (without oxygen).
- Temperature of 30-40 degrees C (the optimum temperature for the enzyme produced by yeast.
Give the equation for the fermentation of glucose to form ethanol.
C6H12O6 (aq) —> 2C2H5OH (aq) + 2CO2 (g)
How does the process of fermentation of glucose to form ethanol work?
Yeast is used in anaerobic conditions and produces an enzyme which converts sugars, such as glucose, into ethanol and carbon dioxide.
Why is a temperature of 30-40 degrees C used in the fermentation of glucose?
The enzyme produced by yeast functions at an optimum temperature. If the temperature is too cold, the reaction is slow, if it’s too hot, the enzyme is denatured.
What happens once ethanol is formed by the fermentation of glucose?
Ethanol is separated from the rest of the mixture using fractional distillation.
What are the advantages of fermentation?
- It’s low-tech so uses cheap equipment.
2. Uses renewable resources.
What are the disadvantages of fermentation?
Fractional distillation is required which takes extra time and money.
Why is air kept out of a fermentation vessel?
To prevent the oxidation of an alcohol.
What type of fuel can ethanol be used as?
A biofuel - bioethanol.
Why can bioethanol be thought of as carbon neutral? Give equations to support this statement.
Bioethanol does produce CO2 when burnt but the plants used to make the bioethanol take in the same amount of CO2 when growing. This is seen as carbon neutral.
Equations:
- Plants take in CO2 from the atmosphere to produce glucose by photosynthesis where 6 moles of CO2 are taken in by the plant
6CO2 + 6H2O —> C6H12O6 + 6O2
- Glucose is converted into ethanol in fermentation where 2 moles of CO2 are produced
C6H12O6 —> 2C2H5OH + 2CO2
- When ethanol is burned, 4 moles of CO2 and water are produced
2C2H5OH + 6O2 —> 4CO2 + 6H2O
So 6 moles of CO2 are taken in and 6 moles are given out.
Why, in reality, are biofuels not carbon neutral?
Fossil fuels will need to be burned to power the machinery used to make fertilisers for the crops, harvest the crops and refine and transport the bioethanol. Burning the fuel to power this machinery produces carbon dioxide.
