alcohols (organic) Flashcards
What is the functional group of an alcohol?
Hydroxyl group -OH
General formula of an alcohol
CnH2n+1OH
How do you name alcohols (1 prefix, 1 suffix)
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’ melting point and boiling points compare to other hydrocarbons of similar C chain lengths? 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 1 other carbon atom
What makes an alcohol secondary?
C bonded to OH is bonded to 2 other carbon atoms
What makes an alcohol tertiary?
C bonded to OH is bonded to 3 other carbon atoms
How can ethanol be made from crude oil?
Hydration of ethene via electrophilic addition (phosphoric acid catalyst H3PO4)
What are the advantages and disadvantages of this method? (hydration)
Advantages - fast, continuous process, ethanol has a high purity.
Disadvantages - 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 fermentation to take place?
Enzymes in yeast as catalyst, 35’C, anaerobic conditions
Write an equation for fermentation?
C612O6(aq) > 2C2H5OH + 2CO2
What are 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 ethene be made? Why is it not 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 as fuel?
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 (toxic so it can’t be drunk)
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 alohols?
OH and a H (to form water)
What physical conditions are needed for the elimination reaction from alcohols to alkenes (2 alternatives)
Excess hot concentrated sulfuric acid or pass vapour over 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 sulfuric acid, potassium dichromate (VI), distill product as its produced, gentle heating
equation for the partial oxidation of ethanol
CH3CH2OH(l)+ [O] > CH3CHO(g) + H2O(l)
What forms if you fully oxidise a primary alcohol?
A carboxylic acid
What conditions are needed to fully oxidise a primary alcohol?
Concentrated sulfuric acid, potassium dichromate (VI), reflux for about 20 mins, strong heating
equation for full oxidation for ethanol
CH3CH2OH(l) + 2[O] > CH3COOH(g) + H2O(l)
What forms if you oxidise a secondary alcohol?
a ketone
Why can a secondary alcohol not be oxidised further / why cant a tertiary alcohol not be oxidised?
A C-C bond would have to break
What conditions are needed for the oxidation of a secondary alcohol?
Concentrated sulfuric acid, potassium dichromate (VI), reflux for about 20 minutes, strong heating
equation for the oxidation of propan-2-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 (ethanal)
What is a ketone? What is its functional group?
Molecule with C=O group in the middle of a carbon chain, carbonyl group (C=O)
How do you name ketones? Give an example
Suffix -one (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 (propanoic acid)
What does the Tollens’ test give a positive result for?
aldehydes
What is in Tollens’ reagent? 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 substance being tested and tollens reagent to a test tube, leave in water bath for 10 minutes 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 Fehlings? How does this react with the substance to be tested?
Blue copper (II) complex ions - gentle oxidising agent.
Reduced 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
