3.3.5.1 Alcohol production
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Why do alcohols have a greater boiling point than alkenes with similar Mr?
Both have VdW forces of similar strength (Mr is similar so number of electrons is similar). However alcohols have hydrogen bonding as well, which is stronger than the VdW forces in the alkene
Describe the solubility of alcohols
The O-H group allows for solubility in polar solvents e.g. H2O as the O-H group can form hydrogen bonds with H2O molecules. This is true for shorter molecules, but as the alkyl group length increases, the non-polar forces begin to dominate and the solubility in polar solvents decreases.
What are the three classifications of alcohols?
Primary Secondary Teriary
What does the classification of alcohols depend on?
The number of alkyl groups attached to the carbon that holds the O-H group e.g. one alkyl group implies primary alcohol
What are the two ways to produce alcohol?
Fermentation Hydration of ethene
Describe alcohol production through the hydration of ethene
C2H4 +H2O <-> C2H5OH Mechanism: electrophilic addition Catalyst: phosphoric acid (H3PO4) Pressure: 60 atm Temp.: 600K High yield: Increase the amount of ethene/ use excess of ethene
Why is phosphoric acid used as a catalyst in the hydration of ethene over sulfuric acid?
Phosphoric has more hydrogen ions that dissociate so more acidic
Describe alcohol production through fermentation
C6H12O6 -> 2C2H5OH + 2 CO2 Catalyst: Yeast catalyst (enzyme) Conditions: Anaerobic conditions - prevents oxidation of ethanol to ethanoic acid Temperature: compromise temperature of 37 deg. C or 35 deg. C pH: Neutral
What happens if extreme temperatures are used in fermentation?
Too high: enzyme denatures Too low: Slow rate of reaction
What happens if the concentration of ethanol gets too high in fermentation and what can be done about this?
The enzymes lose function - ethanol is removed from the reaction mixture through fractional distillation
Compare fermentation and hydration of ethene
Raw material: sugars from plants and trees are renewable/ cracking of crude oil, non-renewable Type of process: Batch process/ Continuous process Rate of reaction: Slow/ Fast Quality of product: Imputer; ethanol has to be removed from aqueous mixture/ Pure Reaction conditions: Temp and pressure is low/ Temp/ pressure is high so more energy and more expensive
What is a biofuel?
Any fuel made from plants or animal waste
What is bioethanol?
Made from the fermentation of sugar (sugar beet or sugar cane) followed by fractional distillation
What are carbon neutral activities?
Those in which the total amount of CO2 produced is equal to the total amount of CO2 taken in i.e. net zero emissions of CO2
Why can biofuels not be considered carbon neutral?
CO2 is released during the planting, harvesting and transport, as they burn fossil fuel and release CO2