Summary notes for AQA A-Level Chemistry Unit 3.3.5 - Alcohols
14 views 0 purchase
Course
Unit 3.3.5 - Alcohols
Institution
AQA
Book
AQA A Level Chemistry Student Book 1
Summary notes for AQA A-Level Chemistry Unit 3.3.5 - Alcohols by an Imperial College London MSci Chemistry graduate. Notes divided into the following sections: Physical Properties of Alcohols, Classification of Alcohols, Ethanol Production, Oxidation of Alcohols, Elimination
Summary notes for AQA A-Level Chemistry Unit 3.3.6 - Organic Analysis
Summary notes for AQA A-Level Chemistry Unit 3.3.4 - Alkenes
Summary notes for AQA A-Level Chemistry Unit 3.3 - Halogenoalkanes
All for this textbook (5)
Written for
A/AS Level
AQA
A Level Chemistry
Unit 3.3.5 - Alcohols
All documents for this subject (26)
Seller
Follow
bookishresearcher
Content preview
Section 3: Organic Chemistry
Alcohols
Alcohols are a homologous series w/ the general formula CnH2n+1OH and the functional group -OH.
Physical Properties of Alcohols
Alcohols have a higher b.p. than alkanes w/ a similar Mr because…
• When a molecular covalent liquid is vaporised, energy is supplied to break the intermolecular forces
of attraction between the molecules.
• Alkane molecules are held together by van der Waals’ forces.
• Alcohol molecules are held together by both van der Waals’ forces + hydrogen bonding.
• Hydrogen bonding is stronger than the weak van der Waals’ forces ∴ alcohols = higher b.p.
• Alcohols are soluble in water as they can hydrogen bond w/ water molecules. Alkanes are not soluble
in water as they contain no hydroxyl groups + ∴ can’t hydrogen bond w/ water molecules.
• The greater the no. of hydroxyl groups, the greater the no. of H-bonds + ∴ the greater the solubility
of the alcohol.
Classi cation of Alcohols
Alcohols are classi ed as primary, secondary + tertiary depending on the position of the -OH group in
the carbon chain and the no. of alkyl groups, R groups, attached to the carbon bonded to the -OH group.
Methanol is classi ed as a primary alcohol as the -OH group is at the end of the chain.
Ethanol Production
Ethanol is used as a solvent to make many common substances such as detergents + pharmaceuticals.
It is also used as a solvent to remove ink or paint stains.
Fermentation of Glucose
Ethanol can be produced by the fermentation of glucose, which is a batch process (this is inef cient).
• Raw materials: crops (such as maize, sugar cane and sugar beet) = renewable resource
• Conditions: Temperature: 35°C (as below this temp. reaction rate = too slow + above this
temp. enzymes in yeast are denatured ∴ compromise temp. used)
Pressure: 1atm
Catalyst: enzymes produced by yeast
Other: anaerobic conditions (to prevent the oxidation of ethanol to ethanoic acid)
• Energy requirements: low
• Reaction rate: slow (due to lower temp.)
• Costs: high labour costs
low equipment costs
• Purity of ethanol: impure as it also contains water (fractional distillation used to make it pure)
• Atom economy: 75%
• Product yield: fairly low (because at high ethanol conc. the enzymes in yeast stops functioning)
fi fifi fi
, Section 3: Organic Chemistry
Biofuels
Ethanol produced industrially by fermentation is separated by fractional distillation to make it pure +
can then be used as a biofuel.
• Biofuel: a fuel produced from plants or material derived from plants (biomass).
Advantages of biofuel use…
• biofuels are renewable energy sources ∴ more sustainable.
• most biofuels are considered carbon-neutral (although this is not quite true - see below).
Disadvantages of biofuel use…
• if countries start using land to grow biofuel crops instead of food, they may be unable to feed
everyone in the country.
• it takes a long time to grow the crops and they are subject to the weather + climate.
• in some places, deforestation may occur to create more land to grow crops for biofuels. Deforestation
destroys habitats + removes trees, which means less carbon dioxide is taken in. Trees that are cut
down are also often burnt, releasing even more carbon dioxide.
• fertilisers added to soils to increase biofuel production can pollute waterways, + some fertilisers also
release nitrous oxide (a greenhouse gas).
• practical problems including the fact that most current car engines would be unable to run on fuels
w/ high ethanol concentrations w/out being modi ed.
Is ethanol a carbon-neutral biofuel?
Carbon-neutral activity: one in which there is no net annual emissions of carbon dioxide into the
atmosphere.
∴ a fuel can be considered carbon neutral when the amount of carbon dioxide released when the fuel is
manufactured + combusted = the amount of carbon dioxide absorbed when the raw material is grown.
So bioethanol is sometimes thought of as a carbon neutral fuel. Here are the chemical equations to
support that argument:
1. During photosynthesis, 6 moles of carbon dioxide are absorbed from the atmosphere to produce 1
mole of glucose:
2. During fermentation, 2 moles of carbon dioxide are released into the atmosphere when 1 mole of
glucose is converted to 2 moles of ethanol:
3. During the combustion of ethanol, 4 moles of carbon dioxide are released into the atmosphere when
2 moles of ethanol are burned completely.
Combining all 3 equations shows that 6 moles of carbon dioxide are absorbed + exactly 6 moles of
carbon dioxide are released back into the atmosphere. This shows that bioethanol can be considered a
carbon neutral fuel.
HOWEVER, energy is required to power the machinery used to make fertilisers for the crops + the
machinery used to harvest the crops. Re ning + transporting bioethanol also uses a lot of energy, and
this energy comes from fossil fuels. Burning fossil fuels produces carbon dioxide, which is released into
the atmosphere. ∴ bioethanol isn’t a completely carbon neutral fuel.
fi fi
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller bookishresearcher. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $3.87. You're not tied to anything after your purchase.
