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LAB in Condensation, Chemical Change, Functional Groups, Lewis Structures. Last updated October 14, 2019.

Summary

In this lab, students will use Lewis structures to explain the mechanism of an organic condensation reaction between a carboxylic acid and an alcohol, also known as an esterification reaction and is an example of a condensation reaction.

Grade Level

High school

Objectives

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

  • Identify functional groups in an organic compound.
  • Determine the mechanism of a condensation reaction.
  • Understand an esterification reaction.

Chemistry Topics

This lesson supports students’ understanding of

  • Functional groups
  • Organic chemistry

Time

Teacher Preparation: 30 minutes

Lesson: one class period

Materials

  • Hot plate
  • 100-mL or larger beaker
  • Water
  • Test tube
  • Methanol
  • Pipet
  • Balance
  • Salicylic acid
  • Scoopula
  • **Concentrated H2SO4 (not for students to handle)

Safety

  • Always wear safety goggles when handling chemicals in the lab.
  • Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.
  • Keep methanol away from open flames as it is highly flammable.
  • **Concentrated H2SO4 must be used as the catalyst. Do not allow students to handle the concentrated acid because it will burn skin and fabric immediately on contact. Handle H2SO4 with extreme care and only have a small quantity in the lab area when conducting the experiment.
  • 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.

Teacher Notes

  • Students should note the wintergreen/mint smell that the reaction produces.
  • Salicylic acid is 2-hydroxybenzoic acid (C7H6O3)
  • Other combinations of carboxylic acids and alcohols (about 10 drops of each) that result in distinct scents are as follows:
    • Octanol + acetic acid  ⇾ orange
    • 3-Methyl-1-butanol + acetic acid ⇾ banana
    • Pentanol + acetic acid ⇾ sour apple
    • 2-Methyl-1-propanol + formic acid ⇾ cherry/cough drop

For the Student

Lesson

Prelab Question

What reaction types have you learned about so far this year?

Background

In this lab, you will learn about another kind of reaction—condensation. Look at the name of this reaction. What kind of product do you think results?

Here is an example of a condensation reaction:

Ethanoic acid + Methanol ⇾ Methyl ethanoate + Water

Notice the H2SO4 over the arrow. What does that mean?

Fill in the rest of the chart with the information. Pay close attention to the functional groups involved in the reaction:


Reactants Products Description

This specific type of condensation reaction is known as an esterification reaction. Why do you think that is true?

Condensation reactions are extremely useful and common in everyday life. Esters tend to have sweet and fruity smells. If this is the case, what kinds of products do you think could be made from esters?

Procedure

  1. Make a water bath by filling a 100-mL beaker with 50 mL of water. Place the beaker on a hot plate and bring the water to a gentle boil.
  2. While you’re waiting for the water to come to a boil, complete the information in the data table about the two chemicals you will use in this experiment.
  3. In a test tube, add 5 drops of methanol.
  4. On a balance, mass out 0.10 g of salicylic acid.
  5. Add the salicylic acid to the test tube.
  6. See your teacher so they can carefully add two drops of concentrated H2SO4 to the test tube. Record any observations you have about the reaction.
  7. Place the test tube in the hot water bath.
  8. Keep the test tube in the water for about three minutes. Make sure you use tongs to gently stir the test tube around. Do not spill the contents. Note any observations.
  9. Remove the test tube from the hot water bath and add five drops of cold water. Again, note any observations.
Data/Observations
Chemical Chemical formula Chemical structure
Methanol
Salicylic acid
Step Observations
After adding H2SO4
While heating
After adding cold water

Analysis

  1. Draw the Lewis structures showing the reaction you carried out.
  2. If you replaced methanol with hexanol, how would the product(s) change? Explain.
  3. Why does the –OH react and not the =O in this reaction?
  4. If H2SO4 were omitted from the experiment, would the same results be obtained? Explain.

Conclusion

Identify three other condensation reaction types. You may use outside resources to help you with this.