Organic chemistry - Carboxylic acids (3)
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1.
Question 3
Describe an experimental procedure for carrying out the esterification of ethanoic acid with ethanol, using an acid catalyst and a Dean-Stark apparatus. Include a list of the apparatus required and explain the purpose of each piece of equipment.
Apparatus Required:
- Round-bottom flask (e.g., 250 cm3)
- Condenser
- Gas outlet tube
- Dean-Stark apparatus
- Heating mantle or water bath
- Separatory funnel
- Beaker
- Stirrer
- Ethanoic acid (CH3COOH)
- Ethanol (CH3CH2OH)
- Concentrated sulfuric acid (H2SO4)
Procedure:
- Combine a measured amount of ethanoic acid (e.g., 25 cm3) and ethanol (e.g., 25 cm3) in the round-bottom flask.
- Add a few drops of concentrated sulfuric acid as a catalyst.
- Attach the condenser to the round-bottom flask.
- Connect the gas outlet tube to the Dean-Stark apparatus. Ensure the Dean-Stark apparatus is positioned correctly to collect the water that is produced during the reaction.
- Heat the mixture gently using a heating mantle or water bath. Maintain a steady temperature (e.g., 80-90 °C).
- As the ester is formed, water will be produced. This water will flow into the Dean-Stark apparatus, accumulating in the separatory funnel.
- Continue heating until no more water is collected in the Dean-Stark apparatus (indicating that the reaction has reached equilibrium).
- Remove the heat and allow the mixture to cool.
- Neutralise the acid catalyst by washing the reaction mixture with a dilute sodium carbonate solution.
- Extract the ester from the aqueous layer using a suitable organic solvent (e.g., diethyl ether).
- Dry the organic layer over anhydrous magnesium sulfate.
- Remove the solvent by distillation.
Purpose of each piece of equipment:
- Round-bottom flask: Contains the reaction mixture.
- Condenser: Condenses the vapours, preventing them from escaping.
- Gas outlet tube: Allows the vapour to enter the Dean-Stark apparatus.
- Dean-Stark apparatus: Separates the water produced during the reaction from the organic layer. The water accumulates in the separatory funnel, while the organic layer is collected.
- Heating mantle/water bath: Provides a controlled source of heat to increase the reaction rate.
- Separatory funnel: Used to collect the water from the Dean-Stark apparatus.
- Beaker: Used for mixing and holding solutions.
- Stirrer: Ensures the reaction mixture is well mixed.
2.
Describe how ethanoic acid is produced by bacterial oxidation of ethanol during vinegar production. Include the type of bacteria involved and the conditions required for the reaction to occur.
Ethanoic acid (CH3COOH), commonly known as acetic acid, is produced by the bacterial oxidation of ethanol (CH3CH2OH) during the production of vinegar. This is an example of an anaerobic process, meaning it occurs in the absence of oxygen.
The primary bacteria responsible for this oxidation are Acetobacter species. These bacteria thrive in environments with low oxygen concentrations and are specifically adapted to oxidize ethanol to ethanoic acid.
The process occurs in several stages:
- Anaerobic Conditions: The fermentation process takes place in the absence of oxygen.
- Bacterial Growth: Acetobacter bacteria are introduced to a solution of ethanol.
- Oxidation: The bacteria oxidize the ethanol to ethanoic acid. This is a slower process than the oxidation with acidified potassium manganate(VII).
- Acetic Acid Production: The ethanoic acid produced is then further oxidized to acetic acid.
The conditions required for successful vinegar production include:
- Temperature: The optimal temperature range is typically between 20°C and 35°C.
- pH: A slightly acidic pH (around 4-6) is ideal for bacterial growth.
- Nutrients: The bacteria require nutrients such as nitrogen and phosphorus for growth.
- Cleanliness: Maintaining a sterile environment is important to prevent contamination by other microorganisms.
CH3CH2OH (ethanol) + KMnO4 (acidified) → CH3COOH (ethanoic acid) + MnO2 + KOH + H2O
3.
Ethanoic acid reacts with metals to produce a salt and hydrogen gas. Describe the reaction of ethanoic acid with magnesium, including the chemical equation and the name of the salt produced. Also, briefly explain why the reaction rate might vary depending on the metal used.
Ethanoic acid reacts with metals, generally those higher in the reactivity series than hydrogen, to produce a salt and hydrogen gas. The general equation for the reaction is:
- CH3COOH(aq) + M(s) → CH3CO2M(aq) + H2(g)
Where M represents a metal. For example, with magnesium:
CH3COOH(aq) + Mg(s) → Mg(CH3COO)2(aq) + H2(g)
The salt produced is magnesium ethanoate (Mg(CH3COO)2). The reaction rate depends on the metal's position in the reactivity series. More reactive metals (e.g., sodium, potassium) will react more vigorously and rapidly with ethanoic acid than less reactive metals (e.g., copper, zinc). This is because the energy released during the reaction is greater with more reactive metals, leading to a faster rate of electron transfer.