Alcohols Flashcards
Why do alcohols have relatively high boiling points?
The alcohol (-OH) group is polar. This means that it is able to form hydrogen bonds with other alcohol groups on other alcohols. Hydrogen bonds are the strongest type of intermolecular force and therefore requires a lot of heat energy to break, giving alcohols higher boiling points compared to other organic compounds of similar mass.
Why do alcohols dissolve in water and other organic (non-polar) solvents?
- Alcohol dissolves in water because the alcohol group is able to make hydrogen bonds with the water molecule. This means that water molecules are able to surround alcohol molecules and dissolve it.
- Alcohols dissolve in non-polar solvents because of its non-polar component that allows it to be surrounded by other non-polar molecules.
What is volatility?
The ease that a liquid turns into a gas. Volatility increases as boiling point decreases.
Why does the water solubility of alcohols decrease as the chain length increases?
As the chain length increases, a larger part of the alcohol molecule is non-polar. This non-polar part doesn’t form hydrogen bonds with water and isn’t surrounded by water molecules, making the alcohol molecule harder to dissolve. Due to this, only the first 3 alcohols are soluble in water.
What is a primary alcohol?
An alcohol with the alcohol (-OH) group attached to a carbon with 0 or 1 alkyl group attached to it.
What is a secondary alcohol?
An alcohol with the alcohol (-OH) group attached to a carbon with 2 alkyl group attached to it.
What is a tertiary alcohol?
An alcohol with the alcohol (-OH) group attached to a carbon with 3 alkyl groups attached to it.
What are the conditions required for the hydration of ethene to produce ethanol?
- Presence of phosphoric acid catalyst.
- 300 degrees celsius temperature.
- 80 atm (8,000 KPa) pressure.
What are the advantages and disadvantages of hydration of ethene?
Advantages:
- Continuous process so ethanol can be constantly produced without stopping so long as the reactants are being constantly added.
- Ethanol produced is 100% pure.
- Overall reaction has a 95% yield.
Disadvantages:
- Ethene is obtained through cracking, with raw materials coming from crude oil which is a non-renewable source.
- Lots of energy required to maintain high temperature and pressure, so very expensive.
What are the conditions required for fermentation of carbohydrates to produce ethanol?
- 37 degrees celsius temperature.
- Atmospheric pressure.
- Presence of yeast.
- Absence of oxygen.
What are the advantages and disadvantages of fermentation of carbohydrates?
Advantages:
- Raw materials are carbohydrates that originate from plants which are a renewable source.
- Low temperature and pressure required, so energy costs are low.
Disadvantages:
- Ethanol produced is toxic to yeast and will kill it when ethanol concentration is only 14%.
- Batched process, so yeast and carbohydrate mixture needs to be replaced at set intervals and ethanol is only formed at set intervals.
- Ethanol produced is impure and needs to be distilled to form pure ethanol.
What are some uses of alcohols?
- Ethanol is used in alcoholic beverages.
- Alcohols can be used as a solvent for perfumes and other sundries since they evaporate at room temperature.
- Alcohols can be used as fuels for automobiles. they are especially popular as biofuels.
- Alcohols are used to make methylated spirits that are used to clean paint and ink spills due to the non-polar compound dissolving properties of alcohols. Spirits can also be used as fuels for camping stoves.
- Methanol is used as an additive in high performance fuels as it is very efficient at combustion.
What are the uses of combustion of alcohols?
Combustion of alcohols are exothermic reactions that can be used to produce heat and drive combustion engines.
What are the processes involved in oxidation of primary alcohols?
- Primary alcohols can be oxidised by using acidified dichromate ions as oxidising agent.
- The primary alcohol is heated with a mixture of sulfuric acid and potassium dichromate.
- The primary alcohol undergoes 2 oxidation steps; step 1 produces an aldehyde which can be obtained by immediate distillation. Step 2 produces a carboxylic acid. A carboxylic acid can be quickly and efficiently obtained if the mixture is heated under reflux.
- During this reaction, dichromate ions are reduced to chromium (III) ions.
- Colour of solution changes from orange to dark green.
What are the processes involved in oxidation of secondary alcohols?
- Secondary alcohols can also be oxidised by using acidified dichromate ions as the oxidising agent.
- The secondary alcohol is heated with a mixture of sulfuric acid and potassium dichromate.
- The secondary alcohol only undergoes 1 oxidation step to form a ketone.
- The mixture can be heated under reflux to improve efficiency.
- The solution turns from orange to green due to chromium (III) ions being produced.
