Alcohols (Edexcel IGCSE Chemistry (Modular): Unit 2): Flashcards
Exam code: 4XCH1
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- FrontWhat are Alcohols?
Define alcohol.
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Cards in this collection (25)
Define alcohol.
An alcohol is an organic compound containing the hydroxyl (-OH) functional group. Alcohols are colourless liquids that dissolve in water to form neutral solutions.
Why are alcohols considered a homologous series?
Alcohols are considered a homologous series because they all contain the same functional group (the -OH group) and follow the same naming pattern, differing only by a -CH2- unit.
True or False?
Alcohols dissolve in water to form acidic solutions.
False.
Alcohols dissolve in water to form neutral solutions, not acidic ones. The -OH group does not release H+ ions like an acid does.
All alcohols contain the .......... functional group, which is responsible for their characteristic reactions.
All alcohols contain the -OH (hydroxyl) functional group, which is responsible for their characteristic reactions.
Complete the table of the first four alcohols.
Name
Formula
Methanol
C2H5OH
Propan-1-ol
C4H9OH
Complete the table of the first four alcohols.
Name
Formula
Methanol
CH3OH
Ethanol
C2H5OH
Propan-1-ol
C3H7OH
Butan-1-ol
C4H9OH
How are alcohols named?
Alcohols are named by taking the corresponding alkane name and replacing the final -e with -ol. For example, ethane becomes ethanol.
True or False?
The first four alcohols are commonly used as fuels.
True.
The first four alcohols — methanol, ethanol, propan-1-ol and butan-1-ol — are all used as fuels. They burn in air to release energy.
What is the hydroxyl group?
The hydroxyl group is the -OH functional group found in all alcohols. It is the part of the alcohol molecule responsible for its characteristic reactions.
What are the three ways ethanol can be oxidised?
Oxidation of ethanol can occur by:
Combustion (burning in air)
Aerobic oxidation by bacteria
Treatment with an oxidising agent
What are the products of the complete combustion of ethanol?
The complete combustion of ethanol produces carbon dioxide and water. Ethanol burns with an almost invisible blue flame.
When ethanol is left open in wine, bacteria in the air use .......... to oxidise ethanol into .......... and water, giving wine a sour, vinegary taste.
When ethanol is left open in wine, bacteria in the air use oxygen to oxidise ethanol into ethanoic acid and water, giving wine a sour, vinegary taste.
True or False?
Potassium dichromate turns from green to orange when it oxidises ethanol.
False.
Potassium dichromate turns from orange to green during the oxidation of ethanol to ethanoic acid. The colour change confirms that oxidation has occurred.
Why is ethanol heated under reflux when being oxidised with potassium dichromate?
Ethanol is heated under reflux to prevent volatile liquids from evaporating during the slow reaction. A condenser above the flask returns vapours back into the reaction vessel.
When ethanol reacts with an oxidising agent, the equation can be written as: CH3CH2OH + .......... → .......... + H2O.
When ethanol reacts with an oxidising agent, the equation can be written as: CH3CH2OH + [O] → CH3COOH + H2O.
True or False?
Aerobic oxidation of ethanol by bacteria produces ethanoic acid.
True.
Acetobacter bacteria use oxygen from the air to oxidise ethanol, producing ethanoic acid and water. This is the same acid found in vinegar.
What is used as the oxidising agent when oxidising ethanol in the lab?
Potassium dichromate(VI) in sulfuric acid is used as the oxidising agent. The mixture is heated under reflux and the dichromate turns from orange to green as it oxidises the ethanol.
Complete the table comparing the two methods of manufacturing ethanol.
Feature
Hydration of ethene
Fermentation
Raw material
Temperature
Catalyst
Process type
Complete the table comparing the two methods of manufacturing ethanol.
Feature
Hydration of ethene
Fermentation
Raw material
Ethene (from cracking)
Sugar or starch
Temperature
300°C
25–35°C
Catalyst
Phosphoric acid
Yeast
Process type
Continuous
Batch
What conditions are needed for the hydration of ethene to produce ethanol?
The hydration of ethene requires a temperature of around 300°C, a pressure of 60–70 atm, and a concentrated phosphoric acid catalyst.
True or False?
Fermentation is carried out in the presence of oxygen.
False.
Fermentation is an anaerobic process — it occurs in the absence of oxygen. Yeast enzymes break down sugar into ethanol and carbon dioxide without oxygen.
What is fermentation?
Fermentation is the process by which yeast converts sugar or starch dissolved in water into ethanol and carbon dioxide, in the absence of oxygen.
Why is ethanol production by fermentation described as a batch process?
Fermentation is a batch process because yeast is killed once the ethanol concentration reaches around 15%. The reaction vessel must be emptied and the process restarted rather than running continuously.
In fermentation, if the temperature is too .......... the enzymes in yeast will become .......... and the reaction will stop.
In fermentation, if the temperature is too high the enzymes in yeast will become denatured and the reaction will stop.
True or False?
Ethene used for hydration is obtained by cracking hydrocarbons.
True.
Ethene is a by-product of the cracking of hydrocarbons and is used as the feedstock for the hydration reaction to produce ethanol.
How is ethanol separated from water after hydration of ethene?
After hydration, the ethene is first separated in a condenser (it has a much lower boiling point than ethanol or water). The ethanol and water are then separated by fractional distillation.
What is hydration?
Hydration is a reaction in which water is added across a double bond. In ethanol production, a water molecule adds across the C=C double bond of ethene to form ethanol.
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