Alcohols Flashcards
What are the bond angles in alcohols?
H-C-H bonds and C-C-O are 109.5
H-O-C bond is 104.5
What is the boiling point of alcohols?
- Relatively low volatility and high bp
Why do alcohols have high BP?
- Ability to form H-bond between alcohol molecules
Why can smaller alcohols dissolve in water?
Can form h-bonds to water molecules
What is the oxidising agent that causes alcohols to oxidise?
Potassium dichromate
Describe the partial oxidation of primary alcohols
Reaction: Primary alcohols to aldehyde
Reagent: potassium dichromate (VI) and dilute sulfuric acid
Conditions: warm gently and distil out the aldehyde as it forms
What is the observation for oxidising alcohols?
Orange dichromate ion reduces to green Cr3+ ion
What are the two ways ethanol can be produced?
- Hydration of ethene
- Fermentation
Describe hydration of ethene?
Reagent: Excess steam
Catalyst: concentrated h3po4
Conditions: high temperature, high pressure (60 atm), excess steam
Mechanism: electrophilic addition
Why is high pressure used in hydration?
- Equilibrium shifts to the right as there are fewer gaseous molecules
- Yield of alcohol increases
What is a biofuel?
A fuel produced from plants
What are the conditions for fermentation?
- Anaerobic
- 37 degrees
- Yeast
Why are anaerobic conditions used for fermentation?
Oxygen from air is kept out to prevent oxidation of ethanol to ethanoic acid
Give an advantage and a disadvantage of carrying fermentation at higher temperatures
Advantage: ethanol is produced at a faster rate
Disadvantage: more energy is used
How is pure ethanol obtained from industrial fermentation?
- Use fractional distillation to separate water and ethanol
- They have different BP
- The BP of water is 100 degrees and ethanol is 78 degrees
What is the raw material used in hydration of ethene
Ethene from crude oil- non renewable
What is the raw material used in fermentation?
Sugar- renewable
Is the product of hydration if ethene pure or impure?
Pure
Is the product of fermentation pure or impure
Impure - requires fractional distillation
What is the ROR of hydration of ethene
Fast
What is the ROR of fermentation
Slow
Describe the process of hydration of ethene and fermentation
Hydration of ethene - continuous
Fermentation - batch
What is the cost of hydration of ethene?
High set up cost/ low labour costs
What is the cost of fermentation
Low set up costs/ high labour costs
Define the term carbon neutral
No overall carbon dioxide emission to the atmosphere
- Photosynthesis
- Fermentation
- Combustion
Q) explain why the ethanol produced may not be a carbon neutral biofuel
CO2 is released during planting, harvesting and transport as it burns fuels that release CO2
What is the role of dichromate ions?
Oxidising agent ( electron acceptor)
What is the observation with Fehling’s or Benedict’s solution for ketones?
Stays blue ( no visible change)
What is the observation with Tollen’s reagent for ketones?
No visible change, stays colourless
What is the observation with Fehling’s solution for an aldehyde
Blue to brick red ppt
What is the observation with Tollen’s reagent for an aldehyde
Colourless solution forms a silver mirror
How do you test for carboxylic acids
Reagent: solid sodium carbonate
Observation: effervescence/ bubbles
Outline the mechanism of elimination?
Reagent: concentrated sulfuric acid or phosphoric acid
Conditions: heat/warm
What does the elimination do?
Remove water molecule from alcohol to form alkene
