Alcohols Flashcards
as chem
Describe alcohols..
They have functional group OH
There are:
1) Primary alcohol
(1 alkyl group)
2) Secondary alcohol
(2 alkyl groups)
3) Tertiary alcohol
(3 alkyl groups)
How can alcohols produce alkenes?
-proviidng that the alcohol was made via fermentation of glucose from pants DEHYDRATION reaction can occur.
Water can be eliminated from an alcohol to produce an alkene.
CONDITIONS:
acid catalyst : sulphuric acid/ phosphoric acid
Why is producing an alkene better by using an alcohol made from fermentation?
By using alcohol made from fermentation of plants we are making alkenes more
sustainably.
alternative) Normally alkenes are sourced from crude oil which is non-renewable.
What mechanisms are involved in alcohols?
elimination mechanism
What process is conducted for the dehydration of alcohol and why + how?
Distillation- in order to separate useful alkene from the impurities.
Distillation separates chemicals by boiling point.
What may have to be conducted on top of distillation to ensure majority of impurities are removed?
Further separation and purification. This is done by using a separation funnel and addition of a drying agent.
Identify and describe step 1 FOR MAKING CYCLOHEXENE:
Distillation step:
Add concentrated sulfuric, phosphoric acid and cyclohexanol into a round bottomed flask. Add several anti-bumping granules to allow a smooth boiling process.
Use a heating mantle to warm the reactants up to 83°C (the boiling point of cyclohexanol). We don’t use a Bunsen burner to heat this as the cyclohexanol is flammable.
Chemicals with boiling points less than 83°C will evaporate, enter the condenser, cool down and condense back into a liquid. The condenser has cold running water running through the wall.
The product is collected in a vessel e.g. a conical flask. However this product will still have small amounts of impurities such as unreacted cyclohexanol and water
Identify and describe step 2 FOR MAKING CYCLOHEXENE:
Seperation step:
Add the products from step 1 into a separating funnel (shown to the left). Add water to dissolve soluble impurities an create an aqueous solution.
After allowing the solution to settle, 2 layers will form
Top layer - Impure cyclohexene
Bottom layer - Aqueous layer containing water soluble impurities
Drain the aqueous layer off (remember to remove the stopper)
Identify and describe step 3 FOR MAKING CYCLOHEXENE:
Purification step:
Take the impure cyclohexene from step 2 and add to a round bottomed flask.
Add anhydrous CaCt, (calcium chloride). This is a dehydrating agent and will remove and aqueous substances still remaining.
INVERT the flask and leave for 20-30 minutes.
How are alcohols produced from alkenes? + conditions
Through hydration of alkenes
CONDITIONS:
steam and acid catalyst
300 degrees
60 atm pressure
How is ethanol produced from fermentation?
Fermentation uses yeast in anaerobic conditions. The reaction is exothermic.
glucose–>ethanol + carbon dioxide
c6h12o6–> c2h5oh +2co2
yeast is an enzyme which confers the glucose to products.
Then fractional distillation is used to obtain pure ethanol.
What is the use of Biofuels and what are they made from?
Biofuels are made from dead biological matter and are used as a fuel.
Sugar is fermented to produce the alcohol to be used as a biofuel
What are the advantages and disadvantages of using biofuels?
ADVANTAGES:
Biofuels are renewable so they are a more sustainable than crude oil
Biofuels produce CO, when they are burnt however they are classed as carbon neutral as the CO, is absorbed by the sugar cane when it’s growing.
DISADVANTAGES:
Expensive to convert existing petrol engines to take fuels with a higher concentration of ethanol.
Land that could have been used to grow food is being used to make fuel.
This could cause food shortages in countries that grow sugar cane e.g.
India and Brazil
Why are biofuels not completely carbon neutral?
Fossil fuels are burnt to transport the biofuel across the country, fossil fuels are used to make fertilisers put on the crops and on the machinery to harvest the crop.
What products are made when alcohols are oxidised?
Aldehydes
Ketones
Carboxylic acids
How are alcohol oxidised?
Using acidified potassium dichromate.
It turns from orange to green
What can primary alcohols be oxidised into?
Aldehydes —> carboxylic acids.
What can secondary alcohols be oxidised into?
Ketones through reflux
What determines what product is made from primary alcohols ?
The method used
either distillation or reflux.
Aldehyde produced if DISTILLATION used and oxidising agent.
Carboxylic acid produced if REFLUX used and excess oxidising agent.
How to distinguish between aldehydes and ketones?
Using Fehling’s solution or Tollens reagent
Results using Fehling’s solution
If aldehyde is present : Blue precipitate into a red precipitate of Cu2O.
Ketones do not react
Results using Tollens’ reagent?
No reaction with ketones
Aldehydes only get oxidised
If aldehyde present a silver mirror forms coating inside of test tube
