Preparing Esters

This practical lesson covers:

  1. How to prepare a sample of an ester such as ethyl ethanoate

Preparation of ethyl ethanoate


Aim

To prepare a sample of an ester such as ethyl ethanoate.

Background information

Esters are formed through a reaction between an alcohol and a carboxylic acid in the presence of a concentrated acid catalyst, usually sulfuric acid. This process is called esterification. In this practical, you will prepare a sample of ethyl ethanoate by reacting ethanol with ethanoic acid using concentrated sulfuric acid as a catalyst. The ester is then purified by removing impurities with sodium carbonate and calcium chloride solutions.

Equipment

  1. Thermometer
  2. Condenser
  3. 250 cm3 beaker
  4. Clamp and stand
  5. Bung
  6. Electric heater
  7. Dropping pipette
  8. Measuring cylinder
  9. Round bottomed flask with delivery arm
  10. Ethanoic acid
  11. Ethanol
  12. Concentrated sulfuric acid
  13. Sodium carbonate
  14. Calcium chloride solution

Method

  1. Attach the round-bottomed flask to a clamp stand. The condenser should be connected to the round-bottomed flask via a delivery tube. 
  2. Place a beaker at the open end of the condenser. 
  3. Add 10 cm3 ethanol, 12 cm3 ethanoic acid and 15 drops of concentrated sulfuric acid to the round-bottomed flask. 
  4. Reconnect the round-bottomed flask to the apparatus and turn on the tap for the condenser. 
  5. Gently heat the mixture using an electric heater. The ester will condense in the condenser before being collected in the beaker. 
  6. Stop heating when no more ester is vapourising. 
  7. Small quantities of sulfuric acid, ethanoic acid and ethanol may also be collected in the beaker. Add sodium carbonate to remove any acidic impurities. Stop adding sodium carbonate when the solution stops fizzing. 
  8. Add calcium chloride solution to remove the ethanol. 

Safety

  1. Be careful with fragile glassware.
  2. Concentrated sulfuric acid is very corrosive. Take care to avoid contact with the skin. Wash skin immediately if in contact with the acid. 
  3. Ethanol and ethanoic acid are flammable so ensure there are no naked flames.
  4. Keep the laboratory well ventilated. 

What are esters formed from?

A reaction between an alcohol and a carboxylic acid

A reaction between an acid and a salt

A reaction between an acid and a base

A reaction between a salt and a water

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What is the process of forming esters called?

Fermentation

Evaporation

Esterification

Distillation

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What is used as a catalyst in the process of esterification?

Sodium carbonate

Ethanoic acid

Concentrated sulfuric acid

Calcium chloride

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What is the purpose of adding sodium carbonate to the mixture in the beaker?

To increase the acidity of the mixture

To remove any acidic impurities

To cause a reaction with the ethanol

To create a base for the ester

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What is the purpose of adding calcium chloride solution to the mixture in the beaker?

To increase the acidity of the mixture

To create a base for the ester

To remove the ethanol

To cause a reaction with the ethanoic acid

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What safety measure should be taken when handling concentrated sulfuric acid?

Be careful with fragile glassware

Keep the laboratory well ventilated

Ensure there are no naked flames

Avoid contact with the skin and wash immediately if contact occurs

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What is the function of the condenser in the preparation of esters?

The condenser heats the mixture

The ester will condense in the condenser before being collected in the beaker

The condenser measures the amount of ester produced

The condenser adds concentrated sulfuric acid to the mixture

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What is the name of the process that forms esters?

Esterification

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