9.26-9.34 - Alcohols and carboxylic acids
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Describe the formulae of molecules of the alcohols
General formula = Molecular: CnH2n+1OH
State the first 4 alcohols and their formulae
-Methanol CH₃OH -Ethanol C₂H₅OH -Propanol C₃H₇OH -Butanol C₄H₉OH
What is the functional group in alcohols?
–OH
Describe the method for the core practical to investigate the temperature rise produced in a known mass of water by the combustion of alcohols ethanol propanol, butanol and pentanol.
-Measure the initial mass of the burner -Measure the initial temperature of the water -Use a stand and clamp to secure the beaker with a thermometer and the water in it over the burner -Heat the water with the spirit burner until its temperature has increased by 20℃, then replace the burner’s lid to put the flame out -Measure the final temperature of the water -Measure the mass of the spirit burner -Repeat with different alcohols, starting with fresh water each time
Describe and explain the results for the core practical on investigating the temperature produced as a result of the combustion of alcohols
The change in mass is equal to the the mass of fuel burned. The longer the carbon chain length of the alcohol, the less mass is required to cause the same temperature rise because the combustion of the longer chain releases more energy.
Recall the formulae of molecules of the carboxylic acids
They increase by CnH₂n and start with HCOOH
List the first 4 carboxylic acids and their formulae
Methanoic acid HCOOH Ethanoic acid CH₃COOH Propanoic acid C₂H₅COOH Butanoic acid C₃H₇COOH
What is the functional group in carboxylic acids?
-COOH
Describe how an alcohol can produce a carboxylic acid
Ethanol can be oxidised to produce ethanoic acid. This extends to other alcohols. Alongside the acid, water and the element that is the first half of the oxide compound are produced.
Describe the relationship between members of the same homologous series.
Members of a given homologous series have similar reactions because their molecules contain the same functional group. This can be used to predict the products of other members of these series.
Describe the production of ethanol by fermentation of carbohydrates
Ferment carbohydrates in aqueous solution, using yeast to provide enzymes. A warm temperature and anaerobic conditions are required. Glucose –> ethanol + carbon dioxide
Explain how to obtain a concentrated solution of ethanol by fractional distillation of the fermentation mixture
Ethanol concentration after fermentation is low so ethanol must be separated from the reaction mixture using fractional distillation. Water and ethanol solution are heated. The ethanol evaporates first (due to a lower boiling point), cools and then condenses — followed by the water doing the same.