2.7 Alcohols And Carboxylic Acids Flashcards
Describe the method of preparing ethanol by hydration of ethene
Ethene is obtained by cracking hydrocarbons.
EXAMPLE equation is CH2=CH2+H20G <—> CH3CH2OH
It is an example of a hydration reaction:
Reagent: water (steam).
Conditions: phosphoric acid catalyst (H3PO4), 300˚C and 6MPa.
Observation: no visible change.
Mechanism: electrophilic addition.
Physical properties of alcohol
Smaller chain alcohols are soluble in water due to their ability to hydrogen bond with water molecules.
Methanol and ethanol are completely soluble in water, but solubility decreases as the hydrocarbon chain length increases. Hydrogen bonding still occurs between water and the hydroxyl group, but the hydrocarbon chain disrupts bonding between other water molecules. These chains can only interact with the water molecules via Van der Waals forces.
Describe the differences in boiling points of alkanes and alcohols
Alcohols can have both Van der Waals forces (between their carbon chains) and hydrogen bonding (between the alcohol groups), whereas the corresponding alkane only has Van der Waals forces so can be separated more easily.
Why is ethanol soluble in water but ethane is not
Only ethanol forms hydrogen bonds with water, due to the electronegative oxygen attracting to the delta positive hydrogen of water. ethane doesn’t form hydrogen bonds due to having no OH group.
How can ethene be converted to ethanol and ethanol to ethene .
Ethene can be reacted with steam in the presence of a phosphoric acid catalyst at 60-70 atm and heat (300°C) (1)
ethanol can be dehydrated using concentrated sulfuric acid (1)
heat (180°C) and Al2O3 (1)
(electrophilic) addition AND dehydration/elimination reaction (1)
Describe the fermentation process of ethanol
Ethanol is made by the anaerobic fermentation of sugars found in plant-based materials such as wheat and grapes.
Carried out by dissolving sugar in water adding yeast and leaving mixture in a warm place. Yeast contains enzymes that catalyse the reactions eg gluclose
C6H12O6—-> 2C2H5OH +CO2
This process doesn’t produce 100% concentrated ethanol as fermentation stops when the concentration of ethanol reaches around 15% because at these levels enzymes in the yeast cease to function.
Uses of alcohols
-Ethanol has been used for alcoholic drinks.
-Industrial ethanol is mixed with methanol to produce methylated spirits. This can be used as a solvent (as the polar hydroxyl group and the non-polar carbon chain allow it to mix with many types of polar and non-polar compounds)
Ethanol is used as a biofuel and used as a petrol substitute in countries where oil supplies are low.
What is biofuel
Any fuel taken from living or recently living organisms
What is bioethanol?
Bioethanol is produced by the fermentation of sugars in plants and biodiesel is produced from the oils and fats present in the seeds of some plants.
Disadvantages bioethanol
- Land use
Land being used for crops to create biofuels cannot be used for food crops. Also, forests are being destroyed to create land on which to grow plants for biofuels. - Use of resources
Large amounts of water and fertilisers are needed to grow biofuels, therefore growing them can cause problems due to water shortages in some areas. The water can also be polluted due to fertiliser use. - Are they really carbon neutral?
The burning of biofuels and their absorption of carbon dioxide during growth do balance out with carbon neutrality. However, this does not take into account the fuel needed to build factories, transport raw materials and so on.
Advantages of biofuel
- They’re renewable
- The plants that produce biofuels can be grown every year. Waste materials from animals are also used.
- Greenhouse gases help make them ‘carbon neutral’
- Biofuels do produce carbon dioxide, but the plants that make them have taken in carbon dioxide during photosynthesis, making them carbon neutral.
- Economic and political security
Countries that do not have fossil fuels are affected by changes in price and availability when these fuels are imported.
Describe the Dehydration of alcohols to form alkenes
The alcohol can be dehydrated to form an alkene when reacted with either:
hot, concentrated sulfuric acid (H2SO4, >150°C)
hot pumice (Al2O3, >300°C)
phosphoric acid (H3PO4, >300°C).
Why is pentan-1-ol have higher BP than propan-1-ol’
Both compounds have similar hydrogen bonding between molecules (1)
Pentan-1-ol is a larger molecule than propan-1-ol (1)
Pentan-1-ol has more stronger van der Waals forces between
molecules than propan-1-ol (1)
Ethene and ethanol have very different properties. Compare their solubility in water and volatility, giving reasons for the differences
ethanol is soluble in water as it can hydrogen bond to water (1)
ethene is insoluble as it does not contain any FON elements to form hydrogen bonds (1)
ethene is volatile/ a gas at room temperature as it only has weak van der
Waals forces between the molecules and a low boiling point (1)
ethanol has a low volatility as it can hydrogen bond to itself increasing the
energy required to separate the molecules (1)
Oxidation of alcohols to aldehydes
Primary alcohol forms aldehyde to carboxylic acid
Secondary forms ketone
Tertiary forms nothing
Because two hydrogens are lost, one from the alcohol OH and one from adjacent carbon creating a C=O double bond.
What is the Use of acidified potassium dichromate
When it behaves as an oxidising agent acidified potassium dichromate changes colour from orange to green.
This can be used to test for primary and secondary alcohols since they will give a positive reaction but tertiary wont.
Why is Sodium hydrogen carbonate test for carboxylic acids
Because Co2 gas produced so an effervescence is seen and gas can be shown to be co2 by testing it with lime water.
What is an acid base reaction
When an acid and base (metal oxides, hydroxides) mix together, neutralize one another’s properties, and form a salt.
NEUTRALISATION REACTION
esterification reaction
carboxylic acid + alcohol <-> ester + water
Formation of esters from carboxylic acids and alcohols.
Catalysed by the presence of concentrated sulphuric acid.
What is the test for alcohols or carboxylic acid
Esterification since esters produced have sweet fruity odours.
