Alcohols Flashcards
State the test to distinguish an alcohol from a carboxylic acid?
Add sodium hydrogen carbonate
Carboxylic acid: Effervescence
Alcohol: No reaction
How is biofuel ethanol purified?
Using fractional distillation
Why has direct hydration of ethene replaced the fermentation method?
The direct hydration does not require a catalyst
Which compound is formed when 1-phenylethanol reacts with acidified potassium dichromate?
C6H5COCH3
(Phenyl group) + ( C=O ketone)
How to test alcohol has been dehydrated into alkene?
Add bromine water
The solution will turn colourless if alkene is present
Why is sodium carbonate added to the distillate in the dehydration of alcohols involving phosphoric acid?
To neutralise the phosphoric acid
Give a property of anhydrous calcium chloride that allows it to act as a drying agent in dehydration of alcohols?
Anhydrous-absorbs water
Does not react with alkene
Where is the OH group in a primary alcohol?
At the end of the chain
Where is the OH group in a secondary alcohol?
In the body of the chain
Where is the OH group in a tertiary alcohol?
At a branch in the chain
How many R groups does a primary alcohol have?
1
How many R groups does a secondary alcohol have ?
2
How many R groups does a tertiary alcohol have?
3
How are alcohols classified?
Primary, secondary, tertiary according to how many R groups are bonded to the carbon that has the OH group.
Why are short chain alcohols soluble in water?
Soluble due to hydrogen bonding predominating
Why are long chain alcohols insoluble in water?
Non-polar hydrocarbon chain dominates and so alcohol is insoluble in water.
How is ethanol made by fermentation? (Reaction)
Glucose -> ethanol + carbon dioxide
How is ethene produced at present?
Crude oil fractions are cracked , ethene is hydrated so water is added across the double bond
Disadvantages of ethene production by fermentation
-slow rate of reaction
- aqueous solution of ethanol is produced rather than pure
- requires batches rather than continuous production
Advantages of making ethene by carbohydrates (fermentation)
Renewable
Can be viewed as carbon neutral.
Advantages of ethene production by crude oil?
Fast rate of reaction
Continuous process
Essentially pure product
Disadvantages of ethene production by crude oil?
Non renewable - as crude oil is finite resource
Releases CO2
General Equation for the complete combustion of alcohols ?
Alcohol + oxygen -> carbon dioxide and water
What type of reaction are alcohols involved in?
Elimination reactions
Specifically Dehydration as water is lost
Give two dehydrating agents for alcohols?
Phosphoric acid
Sulfuric acid
What can elimination reactions of longer or branched alcohols form?
Mixture of alkenes including E/Z isomers
What are primary alcohols oxidised to?
Aldehydes ( C=O at the end and H at the end )
What can aldehydes be oxidised to?
Carboxylic acids ( C=O bond at end and OH at the end )
What are Secondary alcohols oxidised to?
Ketones ( C=O group within carbon chain)
Can tertiary alcohols be oxidised and why?
Not easily oxidised
Need C-C bond to break
What solution is added to oxidise alcohols to aldehydes and ketones?
Potassium dichromate,acidified with dilute sulphuric acid
What does potassium dichromate act as in the oxidising of alcohols ?
Oxidising agent
What colour change is show in the oxidation of alcohols to aldehydes/ ketones
Orange to green
Tests for aldehydes and ketones?
The tollens (silver mirror) test- silver nitrate in aqueous ammonia
The fehlings test - blue copper solution
Positive result for tollens with aldehyde ?
Silver mirror formed
Positive result for fehlings with aldehyde?
Blue -> brick red precipitate
Disadvantages of production of ethanol by fermentation?
Transport (petrol car engines would have to be modified to use fuels with high ethanol conc)
This burns fuel that releases CO2
Extracting/ planting / harvesting which burns fuel that releases CO2
Why can ethanol production by fermentation be deemed carbon neutral?
CO2 released when it is burnt is balanced by CO2 absorb by the plant
Conditions of ethanol production by fermentation?
Anaerobic - used glucose
30-40 degrees
Yeast - converts sugar into glucose
Balanced reaction for industrial fermentation of glucose ?
C6H12O6 —> 2 C2H5OH + 2CO2
