đŸ”´đŸ”¸2.7 -Alcohols And Carboxylic Acids Flashcards
Define alcohol
A homologous series containing -OH as the functional group
Define fermentation
An enzyme catalysed reaction that converts sugars to ethanol
How is alcohol produced on a large scale? (2)
- Hydration of ethane
2. Fermentation
How is ethane produced on a large scale in the hydration of ethene
By cracking hydrocarbons produced from petroleum, reacting with steam to produce ethanol
Ch2=Ch2(g) + H2O(g) —<> CH3CH2OH(g)
đŸ”ºH = -45 (Exothermic)
What conditions are used in the hydration of ethene?
Compromise temperature of 300degrees, pressure of 60-70 atmospheres and a catalyst of phosphoric acid
What happens to the ethene not converted in the hydration of ethene
Only 5% converted and the remaining is recycled back to the reaction chamber
Basic description of fermentation
Dissolving sugar in water, adding yeast and leaving in warm place
(Process where sugars are converted to ethanol)
Why is yeast essential for fermentation?
It contain enzymes that catalyse the reaction :: C6H12O6 —> 2C2H5OH + 2CO2
C6H12O6 —> 2C2H5OH + 2CO2
How is ethanol separated?
Co2 is gas :: escapes :: 2C2H5OH remaining
Ethanol has boiling point of 80 degrees and :: to separate use fractional distillation
Why is fractional distillation rather than distillation needed to separate ethanol in fermentation?
Boiling temperatures of ethanol (80) and water (100) are quite close together
Define biofuel
A fuel that has been produced using a biological source
What are the two main forms of biofuel
Why can they be used as fuels?
Bioethanol and biodiesel
Can be used as fuels since both burn exothermically
How is bioethanol obtained?
From sugars in plants by fermentation
How is biodiesel obtained?
From the oils and fats present in the seeds of some plants
Name 3 advantages of using biofuels
- Renewable (grown and produced by animal waste)
- Carbon neutral (as plants use CO2 for photosynthesis, then produce CO2 when burnt) :: less overall greenhouse gases
- Economic and political security (countries that don’t have fossil fuels are less dependent on changes in price and availability)
Name disadvantages of biofuels
1) land use (land can’t be used to produce food + forests cleared for biofuel production)
2) resource use (needs large quantities of water and fertilisers to grow :: causes water pollution)
3) not carbon neutral as use Co2 to build/run factories for biofuel production
What forms when an alcohol is dehydrated?
Show an example equation
Dehydrated to form alkenes
E.g CH3CH2CH2OH —> CH3CH=CH2 + H2O
What are most commonly used to dehydrate alcohols
Concentrated sulphuric acid or heated aluminium oxide
Why is the dehydration of alcohol an elimination?
A double bond is produced by the removal of OH from one carbon atom and H from adjacent atom
Define classification of alcohols
Classification into primary, secondary or tertiary according to their structures
What is a primary alcohol
Occurs when the -OH is joined to a carbon that is itself joined to not more than one other carbon atom e.g methanol or propan-1-ol (check book if unsure)
What is a secondary alcohol
occurs when the -OH is joined to a carbon that is itself joined to two other carbon atom
E.g Propan-2-ol
What is a tertiary alcohol
occurs when the -OH is joined to a carbon that is itself joined to 3 other carbon atoms
E.g 2-methyl butan-2-ol
(Check on pg 155 if unsure)
What can be used to oxidase alcohols
How is this carried out?
Acidified potassium dichromate (VI)
Carried out by heating the alcohol with a mixture of aqueous potassium dichromate(VI) and sulphuric acid
What is the oxidising agent usually shown by?
[O]
Write the word equation for the oxidation of a primary alcohol using ethanol as an example: Stage 1
What is the functional group of the main product of This reaction?
Ethanol + [o] —> ethanal + water
(LOOK AT DIAGRAM JESS)
O
||
C-H (an aldehyde)
Write the word equation for the oxidation of a primary alcohol using ethanol as an example: Stage 2
What is the functional group of the main product of This reaction?
Ethanal + [O] —> ethanoic acid
```
Functional group
O
||
C-OH
carboxylic acid e.g ethanoic acid
~~~
Write the word equation for the oxidation of a SECONDARY alcohol using propan-2-ol
Propan-2-ol + [O] —> propone (keytone with functional group (-C=O) and 2 hydrogens removes +water
(DIAGRAM)
Write the word equation for the oxidation of a TERTIARY alcohol using 2-methylpropan-2-ol as an example
No reaction takes place as no hydrogen in the adjacent carbon that can be lost
Write a summary of oxidation reactions (1,2,3)
1) Primary—> aldehydes—> carboxylic acids
2) Secondary—> ketones
3) tertiary alcohols are not oxidised
What is the colour change of acidified potassium dichromate as an oxidising agent?
Orange—> green
Test for primary and secondary alcohols but not tertiary
Define carboxylic acid
A homologous series containing -COOH as the functional group
Name some carboxylic acids and where they’re present
1- Methanoic acid (formic acid) in venom from ant bites
2- ethanoic acid in vinegar
3-citric acid in lemons and other fruits
4-Malic Acid in many fruits
Define a weak acid
An acid that is only partially ionised in aqueous solution
Why are carboxylic acids acidic?
Because they release H+ ions when added to water
Show the carboxylic acid dissociation equation
RCOOH —<> RCOO- + H+
When R is a variable group
What kind of acids are carboxylic acids?
What does this cause?
Weak acids shown through pH and :: the ionisation needed to produce H+ is an equilibrium
What reactions occur with carboxylic acids?
- As an acid
2. Esterification
general word equation and example of carboxylic acid + base
Is there a visible change?
General: acid + base = salt + water
Example using base NaOH
Ethanoic acid —> sodium ethanoate
No visible change as all reagents and products are colourless and soluble in water
General Word equation and example of carboxylic acid + carbonates and hydrogencarbonates
What is observed? How can this be tested?
General: acid + carbonate —> salt + water + co2
Effervescence is seen as co2 produced, gas can be collected and tested with limewater
Give the general equation for esterification
Carboxylic acid + alcohol —> Ester + water
What is esterification catalysed by?
Concentrated sulfuric acid
Describe how esterification is carried out
Heat carboxylic acid with an alcohol and concentrated sulfuric acid
How can you tell esterification is a test for an alcohol/carboxylic acid?
Esters produced gave a sweet fruity odour
How do you obtain a pure sample of an ester?
- Carboxylic acid, alcohol and concentrated sulfuric acid are heated together in a flask
- Produces equilibrium mixture of Ester with some carboxylic acid and alcohol
- Flak is attached to allow the removal of the Ester as soon as it’s formed
(DIAGRAM PG 159)
How does le chatelliers principle support the distilling of Ester
The removal of Ester pulls the equilibrium to the right and more Ester is made
Why can the Ester by distilled off by leaving the other organic substances in the reaction flask
The Ester has the lowest boiling temperature: alcohols, carboxylic acids and water all contain the -Oh group and can hydrogen bond, this increases their boiling temperatures. Esters can’t hydrogen bond
Explain why 2-bromopropane is the main product opposed to 1-bromopropane
- 2 bromopropane is formed from secondary carbocation (1 is from primary carbocation)
- secondary carbocations are more stable than primary carbocations
