Alcohols and Carboxylic Acids - Topic 9 Flashcards
What is the general formula for alcohols?
Are alcohols hydrocarbons?
no as hydrocarbons only contain C and H
What is the functional group of alcohols?
-OH
How can alcohols form alkenes?
alcohols can be dehydrated to form alkenes
Are alcohols flammable?
- alcohols are generally flammable
- they will undergo combustion - this means they can be used as a fuel
- (like all fuels some are better than others)
What happens when alcohols burn?
when alcohols burn they release energy
What could the energy released through the combustion of alcohols be used for?
- this energy could power cars, heat homes and generate electricity
- so alcohols could be used as fuel in place of fossil fuels
Method to investigate different types of alcohol as a fuel:
- Put the alcohol in a spirit burner and measure the mass of the burner and fuel (with lid on)
- Measure 100cm3 of water into a copper calorimeter
- Insulate the calorimeter by using a draught excluder, then cover with an insulating lid after placing a thermometer inside - helps to make sure that minimal energy is lost to the surroundings
- Measure the initial temperature of the water using the thermometer and put the burner under the calorimeter and light the wick
- Stir the water using a glass rod, when heat from the burner has made the temperature of the water ‘rise by 20 degrees C, put the lid of the spirit burner back on the burner to blow out the flame
- Immediately reweigh the spirit burner and subtract the burner and fuels’ original mass - gives you the mass of the fuel burnt
- Repeat the experiment using the other alcohols (ethanol, butanol, methanol, propanol)
Diagram of apparatus used to investigate different types of alcohol as a fuel:
Correlation between formula of the alcohol and its efficiency as a fuel:
- the larger/longer the alcohol e.g. CH4H9OH should be the most efficient
- corresponds to the overall number of bonds being broken but also the number of new bonds being made (exo.)
Control variables when investigating the use of different alcohols as a fuel:
- distance between wick and bottom of can
- method of reducing heat loss
- keep length of wick the same
- check accurate mass (vol) of H2O
- keep same equipment
- volume of water
- volume of alcohol fuel
How can you improve experiment for investigating the use of different alcohols as fuel?
- introduce draught exclusion
- increase insulation
Why do members of a given homologous series have similar reactions?
- members of a given homologous series have similar reactions as their molecules contain the same functional group
- can be used to predict the products of other members of these series
How is ethanol produced?
- fermentation of carbohydrates in aqueous solution
- using yeast to provide enzymes
- solution is warmed
Process of fermentation to produce ethanol:
- produced from carbohydrates (sugars, fruit or starch)
- mixed with yeast and water
- mixture must be kept warm, just above room temperature (20 degrees C - 30 degrees C) and under anaerobic conditions
- must be kept warm so reaction is fast enough but yeast doesn’t denature
- anaerobic otherwise only CO2 and H20 would be produced otherwise
- yeast contains enzymes which are biological catalysts
- if there is oxygen then the enzymes will break down sugar to H2O and CO2 however in conditions without oxygen (anaerobic) the enzymes in yeast catalyse the breakdown of sugar into ethanol and CO2
- CO2 allowed to escape so it does not poison the yeast, but air is not allowed into the reaction vessel so that the yeast continues to produce ethanol
Fermentation equation:
- yeast - enzymes, biological catalyst
How can you obtain a concentrated solution of ethanol?
obtain a concentrated solution of ethanol by fractional distillation of the fermentation mixture
How is factional distillation used to obtain a concentrated solution of ethanol?
- higher conc than ethanol from fermentation
- water and ethanol solution are heated
- ethanol evaporates first (has a lower bp than water), cools and then condenses
- water left evaporates, cools and then condenses
Method for dehydration of ethanol to form ethene:
- the Al2O3 in the test tube is heated and acts as a catalyst for the reaction
- ethanol vapour passes over the catalyst as the water is removed
- it travels through the delivery tubing and a gas (alkene) and water is collected in the inverted test tube
- the gas collected can then be tested with Br2 water
What would you see if bromine water was added to the gas (alkene) collecting in the test tube and why? (dehydration of ethanol)
bromine water (orange/brown) should decolorise
Reaction between product (alkene) and bromine water (dehydration of ethanol):
What can the hydration of ethene and the dehydration of ethanol be regarded as?
the hydration of ethene and the dehydration of ethanol can be regarded as a reversible reaction which can reach a state of equilibrium under the appropriate conditions
What is the functional group of carboxylic acids?
-COOH
What are the properties of carboxylic acids?
weak acids so they only partially dissociate in water - so are in equilibrium
What can ethanol be oxidised to produce?
- ethanol can be oxidised to produce ethanoic acid
- extends to other alcohols
- reagents are not required
How can ethanol be oxidised to make the corresponding ethanoic acid?
- In the laboratory ethanol can have some chemicals added to it which will provide it with the right amount of oxygen to convert it into a carboxylic acid
- Ethanol can be oxidised in the air by standing an open container with the top off
General equation to show the oxidation of ethanol:
Method for making a solution of ethanol by fermentation:
Stage 1 - Fermentation
- Half fill a conical flask with water
- Add 3 teaspoons of sugar and swirl well to dissolve
- Add a teaspoon of yeast
- Place the bung with delivery tube into the flask, with the other end in a boiling tube of limewater
- Leave for a few days in a warm location
Stage 2 - Purification
- Filter the mixture into a flask to remove dead yeast
- Retain a small amount of the mixture in a stoppered test tube for stage 3
- Place the filtrate in the fractional distillation apparatus + include anti-bumping granules
- Heat the mixture so that the ethanol reaches the top of the column (boiling point 78 degrees C)
- Collect the liquid that drips out of the condenser
- Continue to heat until the temperature at the top of the column starts to rise above this
Stage 3 - Testing the Product
- Collect 2 watch glasses and place samples of the product and the mixture from step 7 on them
- Test the flammability of the 2 samples using a splint
Hazards of ethanol:
ethanol is harmful + flammable
4 essential conditions for yeast to respire anaerobically:
- no air/O2 - to prevent aerobic respiration from taking place as it would prevent ethanol from forming
- warm (30-40 degrees C)
- aqueous
- sugar
What happens to the limewater during the experiment of forming ethanol by fermentation?
goes cloudy as CO2 is produced
Why is the temperature not allowed to rise above 80 degrees C in the fractionating column (making ethanol by fermentation)?
would end up collecting water as well as ethanol meaning distillate would no longer be just ethanol
What is the difference between the flammability of the fermentation mixture and the final product from the fractional distillate (making ethanol by fermentation)?
- fermentation mixture is not flammable
- distillate product of ethanol is flammable
Why can the mixture of water and ethanol be separated by fractional distillation (making ethanol by fermentation)?
- water and ethanol have dif. boiling points
- water bp = 100 degrees C
- ethanol bp = 78 degrees C
What can ethanol be used as and what is that?
- ethanol can be used as a biofuel
- a biofuel is a renewable fuel that has been made from living materials
Main advantages of biofuels compared to fuels made from crude oil:
- renewable
- carbon neutral
- saves resources (no crude oil needed)
Methanol molecular formula + displayed formula:
Ethanol molecular formula + displayed formula:
Propanol molecular formula + displayed formula:
Butanol molecular formula + displayed structure:
Methanoic acid molecular formula + displayed structure:
Ethanoic acid molecular formula + displayed structure:
Propanoic acid molecular formula + displayed structure:
Butanoic acid molecular formula + displayed structure:
Oxidation of an alcohol formula:
alcohol + oxygen ——> carboxylic acid + water
Test is a substance is acidic:
- add piece of magnesium ribbon -> bubbles of gas form
- add a metal carbonate -> bubble of gas form
- add a metal oxide and warm -> metal oxide reacts to form solution
- measure pH using pH probe -> pH less than 7
- add an alkali -> a neutral solution produced
