Alcohols Flashcards
What are the functional groups of alcohols?
OH
What is the general formula of alcohols?
CnH2n+2
What type of series are alcohols?
Homologous
What are primary alcohols?
An alcohol with the carbon with the OH group only has one other carbon attached to it
What are secondary alcohols?
An alcohol with two carbons attached to the carbon with the OH group
What are tertiary alcohols?
Alcohols with three carbons attached to the carbon with the OH group
What are the two types of intermolecular forces between alcohol molecules?
Van der Waals forces and hydrogen bonding
Where are van der Waals forces present in alcohols?
Along the carbon chain of the alcohol
Why are van der Waals forces weaker in secondary and tertiary alcohols?
Their structures mean that they can’t lie as closely together
Where are hydrogen bonds present in alcohols?
Between the lone pair on the oxygen of one OH group of one molecule and the hydrogen in the OH group of another molecule
Why can hydrogen bonding be found in alcohols?
Because the OH groups are polar so there’s an attractive force between them
How can we increase the strength of the van der Waals forces?
Increasing the chain length
Which is stronger; hydrogen bonding or van der Waals forces?
Hydrogen bonding
What must happen before an alcohol can boil?
Enough energy has to be transferred from the surroundings to overcome intermolecular forces
Why are alcohols stronger than alkanes?
Alcohols have van der Waals and hydrogen bonding but alkanes just have van der Waals forces
Why are short chain alcohols soluble in water?
Because of the OH group
Why are alkanes insoluble in water?
Because they don’t have the OH group
What are the two ways in which ethanol can be produced?
Hydration of ethene and fermentation of glucose
What is the equation for the hydration of ethene?
C2H4 + H20 —> C2H5OH
What are the conditions used in hydration of ethene?
600K
pressure of 6000-7000Pa
phosphoric(V) acid catalyst in silica pellets
excess ethene for high yield
What is the equation for the fermentation of glucose?
C6H12O6 —-> 2C2H5OH + 2CO2
What are the conditions used in fermentation?
Absence of oxygen, presence of yeast and sugar solution and a temperature of 37-40
Why is yeast needed?
To produce enzymes which convert sugars into methanol
Why are anaerobic conditions needed in fermentation?
To prevent oxidation of ethanol into ethanoic acid
Why is a temperature of 35 needed in fermentation?
Because below 25 the reaction is too slow but above 40 the enzymes denature
When ethanol is formed after fermentation, what is done to it and why?
Yeast is killed by ethanol of a too high % of ethanol so it’s removed from the reaction mixture by fractional distillation and used to make biofuel
What are the disadvantages of fermentation/
Batch process (ineffiecient bc new equipment set up), very slow rate of reaction and impure ethanol produced which needs further purification
What are the advantages of fermenation?
Uses a renewable source and uses gentle temp and pressure
What are the disadvantages of hydration?
Uses finite sources and lot of energy to heat
What are the advantages of hydration?
Continuous flow process (flow over a catalyst) so more efficient, fast and purer ethanol
What is a biofuel?
Any fuel made from living organisms or their waste (biomass)
Why may biofuel not actually be carbon neutral?
Production of fertilisers and pesticide requires energy, transportation of ethanol produces CO2 and fractional distillation of ethanol requires CO2
Advantages of biofuel
Carbon-neutral and sustainable bc using renewable source of energy
Disadvantages of biofuel
Food crops used for fuel - ethical issues
Food crops subject to climate
Growing crops takes time
Gotta purify the ethanol
What is an example of an oxidising agent?
Acidified potassium dichromate (VI) solution
What can the oxidation of a primary alcohol produce?
An aldehyde or a carboxylic acid
What is the functional group of an aldehyde?
CHO
How can you get an aldehyde from a primary alcohol?
Excess primary alcohol
Distill product immediately to prevent further oxidation
How can you get a carboxylic acid from a primary alcohol?
Excess of acidified potassium dichromate solution
Reflux gently
What is the product from the oxidation of a secondary alcohol?
A ketone
What are the conditions for ketones to be formed?
Refluxed with excess potassium dichromate (VI) solution
What is the functional group of a ketone?
CO
Why can’t tertiary alcohols be oxidised?
Because they have no hydrogens attached to the carbon with the OH group attached
What is the C=O group called?
Carbonyl group
What is Tollen’s reagent?
A colourless solution of silver nitrate and dilute ammonia
How does the silver mirror test work?
Tollen’s reagent added to aldehyde and warmed gently, oxidising aldehyde to a carboxylic acid. Silver ions are reduced to atoms which are deposited on the sides to create a silver mirror effect.
What does Tollen’s reagent do in the presence of a ketone?
Does not react and the mixture stays colourless
What is in Fehling’s 1?
Copper sulphate
What’s in Fehling’s 2?
Sodium hydroxide
How is Fehling’s used to test for aldehydes?
Heated with the aldehyde and the blue colour disappears and an orange-red precipitate of copper oxide is formed
What is an elimination reaction?
Where a small molecule is removed from the reactant molecule
What is a dehydration reaction?
When a molecule of water is eliminated
What conditions are needed for the dehydration of alcohols?
Concentrated sulfuric acid catalyst at a temp. of 170 or alcohol vapour over heated aluminium oxide catalyst at 600C
How are alcohols formed?
from the hydration of alkenes with an acid catalyst
Explain what refluxing is?
The continuous boiling, evaporation and condensing of a mixture over a long period of time to ensure a reaction takes place
Why do you add reactants slowly during reflux?
Because reaction is exothermic. Adding slowly dissipates the heat
What are anti-bumping granules?
Small rough pieces of silica which provide a surface for gas bubbles to build up on - promotes smooth and even boiling
Why is a vertical condenser needed in reflux?
To condense evaporated gases back into the reaction mixture - ensures no vapour escapes
Why is there no stopper in the condenser in the reflux equipment?
So that the pressure doesn’t build up
What is the purpose of distillation?
To separate products
Which equations would you use to show that biofuel is carbon neutral?
photosynthesis
fermentation
combustion
How do anti-bumping granules prevent violent boiling?
They provide a surface for gas bubbles to form - prevent large gas bubbles from building up
Define carbon neutral
No net emission of CO2 into the atmosphere
How can you make a more concentrated solution of ethanol from fermentation?
Fractional distillation
Give an equation for the oxidation of a primary alcohol to an aldehyde
Primary alcohol + [O] —-> aldehyde + H2O
Give an equation for the oxidation of a primary alcohol to a carboxylic acid
Primary alcohol + 2[O] —> carboxylic acid + H2O
Give an equation for the oxidation of a secondary alcohol to a ketone
Secondary alcohol + {O] —-> ketone + H2O
