3.5 Alcohols Flashcards
What is the functional group of an alcohol?
Hydroxyl group -OH
What is the general formula of an alcohol?
CnH2n+1OH
How do you name alcohols
Hydroxyl or OH
What kind of intermolecular forces do alcohols have? Why?
Hydrogen bonding, due to the electronegativity difference in the OH bond
How do alcohols m.p and b.p compare to other hydrocarbons of similar C chain length? Why?
Higher because they have hydrogen bonding—> 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 an alcohol primary?
C bonded to OH is only bonded to one other C atom
What makes an alcohol secondary?
C bonded to OH is bonded to two other C atoms
What makes an alcohol tertiary?
C bonded to OH is bonded to three other C atoms
How can ethanol be made from crude oil?
Hydration of ethene via electrophilic addition
What are the advantages and disadvantages of this method?
Advantages- fast, continuous process, ethanol has a high purity
Disadvantage- not renewable as from crude oil
How can ethanol be made by fermentation?
Plant carbohydrates broken down and fermented by enzymes in yeast—> ethanol
What conditions are needed for this reaction to take place?
Enzymes is yeast as catalyst 35 degree Celsius anaerobic conditions
Write an equation for the reaction which take place
C6H12O6(aq) —> 2C2H5OH + 2CO2
What are the 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 fractional 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 —> ethene
Not economical at the moment
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 e.g. transport
What is a commercial fuel that uses ethanol? What else does it contain and why?
Methylated spirits- methanol (toxic-can’t be drunk)
Write an equation for the 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 H (to form water)
What physical conditions are needed for the elimination reaction from alcohols to alkenes? (2 alternatives)
Excess hot concentrated sulphuric acid or pass vapour over hot aluminium oxide
Draw a mechanism for the dehydration of ethanol
Slide 52
Draw a method for dehydration of ethanol in the lab
Slide 54
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
Write an equation for the partial oxidation of ethanol
CH3CH2OH (l) + [O] —> CH3CHO (g) + H2O (l)
What forms of you fully oxidise a primary alcohol
A carboxylic acid
What conditions are needed for this reaction
Concentrated sulphuric acid, potassium dichromate (VI), reflux done for about 20 minutes, strong heating
Write an equation for the full oxidation of ethanol
CH3CH2OH (l) + 2[O] —> CH3COOH (g) + H2O (l)
What forms of you oxidise a secondary alcohol
A ketone
Why can it not be oxidised further and why can’t a tertiary alcohol be oxidised
A carbon-carbon bond would have to break
What conditions are needed for the oxidation of a secondary alcohol
Concentrated sulphuric acid, potassium dichromate (VI), reflux for about 20 mins, strong heating
Write an equation for the oxidation of propan2-ol
CH3CH(OH)CH3 (l) + [O] —> CH3COCH3 (g) + H2O (l)
What is an aldehyde. What is its functional group?
Molecule with C=O group at the end of a carbon chain, carbonyl functional group (C=O)
How do you name aldehydes? Give an example
Suffix - al
e.g. ethanal
What is a ketone? What is its functional group?
Molecule with C=O group in the middle of a carbon chain, carbonyl functional group (C=O)
How do you name ketones? Give an example?
Suffix -one
e.g. propanone
What is a carboxylic acid? What is its functional group?
Molecule with a COOH group, which has to be at the end of a carbon chain
Carboxyl functional group ( made up of carbonyl C=O and hydroxyl -OH group)
How do you name carboxylic acids? Give an example
Suffix -oic acid
e.g. propanoic acid
What does the tollens test give a positive result for
Aldehyde
What is in tollens reagents?
How does this react with the substance to be tested
Silver nitrate in NH3 (aq) - oxidises aldehydes but not ketones
Complex silver (I) ions reduced to Ag(S)
How do you carry out the tollens test
Add equal volumes of substances being tested and tollens reagent to a test tube, leave in water bath for 10mins and observe any changes
What is the result of the tollens test for aldehydes and ketones
Aldehydes - silver mirror forms (solid Ag)
Ketones - no visible change
What does Fehlings solution give a positive test result for
Aldehydes
What is in Fehlings ? How does this react with the substance to be tested?
Blue copper (II) complex ions - gentle oxidising agent
Reduced to Cu+ ions (brick red)
What conditions do you need to use the Fehlings solution
Heat
What result do aldehydes and ketones give in the Fehlings test
Aldehydes - brick red ppt
Ketones - no visible change
