CH15 Alcohols Flashcards
Functional group of an alcohol
Hydroxyl group -OH
General formula
CnH2n+1OH
Prefix and suffix of naming alcohols
Hydroxyl- or -OH
Intermolecular forces do alcohols have - why
Hydrogen bonding - electronegativity difference in OH bond
Alcohols MP and BP compared to hydrocarbons of similar C chain lengths - why
Higher - hydrogen bonding is stronger than van der Waals forces
Are alcohols soluble in water - why does solubility depend on chain length
Soluble when short chain - OH hydrogen bonds to hydrogen bond in water
Insoluble when long chain - non-polarity of C-H bond takes precedence
What makes a primary alcohol
C bonded to OH is only bonded to 1 other C atom
What makes an alcohol secondary
C bonded to OH is bonded to 2 other C atoms
What makes an alcohol tertiary
C bonded to OH is bonded to 3 other C atoms
How can ethanol be made from crude oil
Hydration of ethene via electrophilic addition
phosphoric acid catalyst
What are the advantages and disadvantages of this method
Advantages - fast, continuous process, ethanol ha a high purity
Disadvantages - not renewable as from crude oil
How can ethanol be made by fermentation
Plant carbohydrates broken down and fermented in yeast –> ethanol
What conditions are needed for this reaction to take place
Enzymes in yeast as catalyst, 3 degrees C, anaerobic conditions
Equation for this reaction
C6H12O6 (aq) –> 2C2H5OH + 2CO2
Advantages and disadvantages of this method
Advantages - renewable as from plants
Disadvantages - slow, batch process, enzymes stop working at 15% alcohol so solution is not pure, needed to be fractionally distilled
In the future, how might most ethene be made - why is it not made like this at the moment
Dehydrate ethanol made by fermentation
Not economically viable
Define carbon neutral
No net addition of CO2 to the atmosphere - carbon dioxide released when combusted = carbon dioxide absorbed as a plant
Explain how using ethanol in petrol engines could be considered to be carbon neutral
Carbon dioxide released in fermentation and combustion = carbon dioxide absorbed when growing
Why would it probably not be entirely carbon neutral to use ethanol
Other “carbon costs” associated with it (transport)
What is a commercial fuel that uses ethanol? What else does it contain and why
Methylated spirits - methanol
Equation for combustion of ethanol
C2H5OH (l) 3O2 (g) –> 2CO2 (g) + 3H2O (l)
What is an elimination reaction
The removal of a smaller molecule from a larger one
Which group leaves the parent molecule in the case of alcohols
OH and a H
What physical conditions needed for the elimination reaction from alcohols to alkenes
Excess hot concentrated sulphuric acid or pass vapour of hot aluminium oxide
What forms if you partially oxidise a primary alcohol
An aldehyde
What conditions are needed to partially oxidise a primary alcohol
Dilute sulphuric acid, potassium dichromate (VI), distill product as it’s produced, gentle heating
Equation for partial oxidation of ethanol
CH3CH3OH (l) + [O] –> CH3CHO (g) + H2O (l)
What forms if you fully oxidise a primary alcohol
A carboxylic acid
What conditions are needed for this reaction
Concentrated sulphuric acid
Potassium dichromate (VI)
Reflux
Strong heating
Equation for full oxidation of ethanol
CH3CH2OH (l) + 2[O] –> CH3COOH (g) + H2O (l)
What forms if you oxidise a secondary alcohol
Ketone
Why can it not be oxidised further and why can’t a tertiary alcohol be oxidised
A C-C bond would have to break
What conditions are needed for the oxidation of a secondary alcohol
Concentrated sulphuric acid
Potassium dichromate (VI)
Reflux
Strong heating
Equation for oxidation of propan-2-ol
CH3CH(OH)CH3 (l) + [O] –> CH3COCH3 (g) + H2O (l)
What is an aldehyde - functional group
Molecule with C=O (carbonyl) group at the end of a carbon chain
Suffix of aldehydes
-al
What is a ketone - functional group
Molecule with C=O (carbonyl) group in the middle of carbon chain
Suffix of ketones
-one
What is a carboxylic acid - functional group
Molecule with COOH (carboxyl) group at the end of a carbon chain
Suffix of carboxylic acids
-oic acid
What does Tollen’s test give a positive result for
Aldehydes
What is in Tollen’s reagent
Silver nitrate in NH3 (aq) - oxidises aldehydes but not ketones Complex silver (I) ions reduced to Ag (s)
Result of the Tollen’s test for aldehydes and ketones
Aldehydes - silver mirror forms
Ketones - no visible change
What does Fehling’s solution give a positive result for
Aldehydes
What is in Fehling’s reagent
Blue copper (II) complex ions - gentle oxidising agent Reduced to Cu+ ions (brick red)
Conditions needed with Fehling’s solution
Heat
