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Esterfication (1 Favorite)

LAB in Balancing Equations, Molecular Structure , Functional Groups. Last updated April 25, 2019.


Summary

In this lab, students will make at least six esters from different combinations of available organic acids and alcohols. In addition, they will attempt to identify the scent of each ester that is created.

Grade Level

High School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

  • HS-PS1-5: Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.
  • HS-PS2-6: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
  • Scientific and Engineering Practices:
    • Analyzing and Interpreting Data

Objectives

By the end of this lab, students should be able to

  • Explain how an ester is made.
  • Draw a structural formula for a generic organic (carboxylic) acid.
  • Draw a structural formula for a generic alcohol.
  • Write a balanced chemical equation that produces an ester.
  • Understand the purpose of sulfuric acid in the formation of an ester.

Chemistry Topics

This lab supports students’ understanding of

  • Organic Chemistry
  • Chemical Reactions
  • Balanced Chemical Equations
  • Molecular Structure
  • Functional Groups
  • Organic (Carboxylic) Acids
  • Alcohols
  • Esters
  • Catalysts

Time

Teacher Preparation: 45 minutes

Lesson: 75 minutes

Materials (per lab group)

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.
  • An operational fire extinguisher should be in the classroom.
  • When working with acids, if any solution gets on students’ skin, they should immediately alert you and thoroughly flush their skin with water.
  • 18 M sulfuric acid is particularly dangerous.Students should wear gloves and only handle it under teacher supervision.
  • When diluting acids, always add acid to water.

Teacher Notes

  • Students only need two drops of 18 M sulfuric acid to catalyze the reaction. They should use a pipet that does not corrode in acid. The acid should be kept under the fume hood, surrounded by a lot of baking soda, and be monitored by the teacher when used by a student.
  • A hot plate should be used to heat the water bath.
  • Ensure that all chemicals are kept away from these heat sources. You may want to create a designated space for students to collect and measure materials that is away from the hot plates.
  • Create several sets of small labeled dropper bottles of the alcohols and acids for groups.
  • Be sure that the students do not smell the ester while it is concentrated and hot. It needs to be poured into a beaker of cold water before wafting.
  • Students can be put into groups of two to three.
  • This lab is best for second year advanced level chemistry but can be adapted for first year honors level chemistry.
  • Students should have previously learned about basic organic functional groups including carboxylic acids, alcohols, and esters.
  • Students can make any combination of acid and alcohol, although some smell better than others.Refer to this table for a list of common esters: https://en.wikipedia.org/wiki/Ester

For the Student

Lesson

Background

An ester is an organic chemical compound that is formed when an organic acid reacts with an alcohol. Esters frequently have distinctive odors and are found in flavorings of many fruits and plants. The reaction between an organic acid and an alcohol is shown below:

In the reaction above, R represents organic groups such as hydrocarbons. The –OH from the acid combines with the –H from the alcohol producing water molecules. The R—O— group from the alcohol attaches to the carbon on the acid forming an ester. The reaction is catalyzed by adding some concentrated sulfuric acid. The sulfuric acid is a strong dehydrating agent, forcing the equilibrium to the right and resulting in a greater yield of ester.

An ester is named using the alkyl group from the alcohol as the first word and the name for the anion from the acid is used as the second word. For example, if acetic acid and methanol (methyl alcohol) are reacted, the ester produced is called methyl acetate.

Generally a fruit or a flower may only contain a few drops of ester, giving it a very subtle odor. The odor of natural products is due to more than one substance. For example, the volatile oil from pineapples contains at least six compounds. When prepared in the laboratory in relatively large amounts, an ester may seem to have a pronounced chemical odor. If the ester is not diluted in some way, it may be difficult to recognize the more characteristic odor.

Objective

To prepare a series of esters and identify the odor of each.

Materials (per lab group)

  • Hot plate
  • 400 mL beaker
  • 250 mL beaker
  • Test tube
  • 18 M sulfuric acid (2 drops per ester)
  • Various organic acids including but not limited to: Glacial acetic acid, Salicylic acid, Benzoic Acid, Propionic Acid, Formic Acid
  • Various alcohols including but not limited to: Methanol, Ethanol, Propanol, Butanol

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Wash your hands thoroughly before leaving the lab.
  • Follow teacher instructions for clean up of materials and disposal of chemicals.
  • Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.
  • An operational fire extinguisher should be in the classroom.
  • When working with acids, if any solution gets on your skin, immediately alert your teacher and thoroughly flush skin with water.
  • 18 M sulfuric acid is particularly dangerous. Wear gloves and only handle it under teacher supervision.
  • When diluting acids, always add acid to water.

Procedure

  1. Fill a 400mL beaker half full with tap water. Put it on a hot plate and heat until it reaches a low boil. This will be your hot water bath for the entire experiment.
  2. Select one of the organic acid solutions and place 10 drops in a test tube. If a solid organic acid is chosen, use a small spatula full (about 0.08 g).
  3. To the same test tube, add 10 drops of one of the alcohols.
  4. Then, put on gloves and very carefully, under teacher supervision, add 2 drops of the concentrated sulfuric acid found under the fume hood.
  5. Put the test tube in the hot water bath and allow it to stand for five minutes.
  6. Never try to directly smell the ester while it is hot or concentrated. Pour about 100 mL of tap water into a 250 mL beaker. Add the contents of the test tube and swirl to mix the contents. Be careful not to spill any liquid.
  7. Carefully smell the ester after it is mixed with water by wafting some of the vapors towards your nose to identify the odor.
  8. After identifying the odor, wash the contents of the test tube down the sink with running water. Clean and dry the test tube and proceed to Step 9.
  9. Prepare a minimum of six esters using any combination of acid and alcohol.

Observations

Complete the data table below for each ester produced.

Acid used Alcohol used Ester Produced Odor of Ester

Post-Lab and Analysis Questions

  1. Explain how an ester is made.
  2. Draw a structural formula for a generic carboxylic acid.
  3. Draw a structural formula for a generic alcohol.
  4. Write an equation using structural formulas for the reaction of acetic acid with propanol.
  5. What is the purpose of sulfuric acid in the formation of an ester?
  6. Extension: Select an ester that you use or encounter in your everyday life and research the following information...
    1. What is the name of the ester?
    2. What carboxylic acid and alcohol were used to produce the ester?
    3. How is the ester produced industrially?
    4. Why is the ester important in your everyday life?