3.5 Alcohols Flashcards
What is the functional group of an alcohol?
Hydroxyl group -OH
What is the general formula of an alcohol?
Cn H2n+1 OH
How do you name alcohols?
Hydroxyl- or -OH
What kind of intermolecular forces do alcohols have? why?
Hydrogen boning, due to the electronegative 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 hydrogen bond in water
Insoluble when long chain- non-polarity of C-H bond takes precedence
What make 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 (phosphoric acid catalyst H3PO4)
What are the advantages and disadvantages of making ethanol from crude oil?
Advantages- fast, continuous process, ethanol, has a high purity
Disadvantages- not renewable as from crude oil
How can ethanol be made by fermentation?
Plant carbo hydrates broken down and fermented by enzymes in yeast —> ethanol
What conditions are needed for ethanol to be formed by fermentation?
Enzymes in yeast as catalyst, 35 degrees C, anaerobic conditions
Write an equation for the reaction which takes place when ethanol is being formed by fermentation
What are the advantages and disadvantages of making ethanol by fermentation?
Advantages- renewable as from plants
Disadvantages- slow, batch process, enzymes stop working at 15% alcohol so the solution is not pure, needs 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- 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, so it can’t be drunk)
Write an equation for the combustion of ethanol?
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 (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
Draw a method for dehydration of ethanol in the lab
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
What forms if you fully oxidise a primary alcohol?
A carboxylic acid
What conditions are needed for a primary alcohol to be fully oxidised?
Concentrated sulphuric acid, potassium, dichromate (VI), reflux for about 20 mins, strong heating
Write an equation for the full oxidation of ethanol
What forms if 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
How do you name aldehydes?
Suffix - al
e.g ethanal
Write an equation for the oxidation of propane-2-ol.
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=0)
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?
Suffix -one
e.g propanone
What is a carboxylic acid? What is its functional group?
Molecule with COOH group, which has to be at the end of a carbon chain.
Carboxyl functional group (made up of carbonyl C=O and hydoxyl OH- group)
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 mins and observe any changes
What is the result of the Tollens’ test for aldehydes and ketone?
Aldehydes- silver mirror forms
Ketones- no visible change
What does Fehling’s solution give a positive test result for?
aldehydes
What is in Fehling’s? 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 condition do you need to use the Fehling’s solution?
Heat
What result do aldehydes and ketone five in the Fehling’s test?
Aldehydes- brick red ppt
Ketones- no visible change
