3.5 Alcohols Flashcards
What is the alcohol group?
- OH
What are the bond angles involved in an alcohol?
- 109.5 between H-C-H and C-C-O because there are 4 bond pairs (tetrahedral)
- 104.5 between H-O-C because there are two bond pairs and two lone pairs
What is a primary alcohol?
1 carbon is attached to carbon with OH
What are the properties of alcohols?
- Polar molecules
- Soluble in water due to H bonds forming
- Low volatility
- Less acidic than water
What is the group of ketones of aldehydes?
Carbonyl group - C=O
What is the oxidation agent used with Alcohols?
- Acidified Potassium dichromate (dilute H2SO4)
What does partial oxidation of a Primary alcohol produce?
- Aldehyde
What does partial oxidation of a secondary alcohol produce?
Ketone
What does full oxidation of a Primary alcohol produce?
Carboxylic acid
What are the conditions for partial oxidation of a primary alcohol?
Warm gently and distill out aldehyde, use limited amount of acidified dichromte
What are the conditions for full oxidation of primary alcohols?
Excess of dichromate, heat under reflux
What is the test for carboxylic acid?
Add sodium carbonate, will fizz if an acid to produce CO2 which can be tested with limewater
What are the conditions to Oxidise a secondary alcohol?
Heat under reflux
Why can tertiary alcohols not be oxidised by potassium dichromate?
Because there is no hydrogen bonded to carbon with the OH group.
What are the two tests for aldehydes/ketones?
Tollens reagent
Feelings solution
What are the reagents,reactions,conditions and observations in using Tollens reagent?
Reagent- Formed using aqueous ammonia and silver nitrate
Reaction- Aldehydes are oxidised into carboxylic acid and silver ions become silver atoms
Conditions- Heat gently
Observations- Aldehydes- silver mirror forms inside test tube
Ketones- no visible change
What are the conditions,reagent,reaction and observations of Fehilings solution?
Reagent- feelings containing blue Cu2+
Conditions- Heat gently
Reaction- Aldehydes oxidised into carboxylic acid, Cu2+ ions reduced to copper
Observation- Aldehydes- Turns from blue to brick red precipitate
Ketones- No change
What is the colour change of acidified Potassium Dichromate?
Orange to green
Why do you not seal the top of a reflux apparatus?
Because it will explode
Definition of elimination?
- Removal of a small molecule
What are the conditions for elimination of alcohols?
- Concentrated H2SO4 in excess
- Vapours heated over Al2O3
What does the elimination of alcohols form?
Alkenes and water
What are the disadvantages of dehydration (elimination) of alcohols?
Conc H2SO4 is a strong oxidising agent:
- CO2 + SO2 can be formed which need to be removed by passing through NaOH solution
So H3PO4 is used which is safer but more expensive
What is the equation for fermentation?
C6H12O6 —-> 2C2H5OH + 2CO2
What are the conditions for fermentation?
35c
1 atm
Yeast catalyst
What is the equation for industrial production of ethanol?
C2H6 + H2O —-> C2H5OH
What are the conditions for industrial ethanol production?
300 c
60 atm
Phosphoric acid catalyst
What comparative points are there between ethanol production by fermentation or industrial?
Renewable vs Non renewable
Slow vs Fast
Batch vs Continuous
Impure vs Pure
‘Carbon neutral’ vs CO2 producing
What does carbon neutral mean?
- CO2 release when burnt is balanced by CO2 absorbed during photosynthesis
Why is carbon neutral not always correct?
Doesn’t take in to account CO2 released during farming,transport etc.
What is a biofuel?
A fuel made from biological material that has recently died
What are the advantages/disadvantages of using biofuels?
Advantages- Renewable,carbon neutral,regrowing plants
Disadvantages- Engines need to be modified,time consuming,still produces CO2
