Topic: Carboxylic acids – properties

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

IX. Hydrocarbon derivatives. Student:

5) tests and describes selected physical and chemical properties of ethanoic (acetic) acid; writes, in molecular form, chemical equations for the reaction of this acid with hydroxides, metal oxides, metals; tests the reaction of an aqueous solution of ethanoic (acetic) acid; writes the equation for dissociation of this acid.

General aim of education

The student investigates and describes selected physical and chemical properties of ethane (acetic) and formic acid

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn;

• mathematical competence and basic competences in science and technology.

Criteria for success
The student will learn:

• to write the equations for the dissociation of carboxylic acids;

• to write the equations for the reaction of obtaining carboxylic acid salts;

• how to plan and carry out an experiment to examine the physical and chemical properties of ethanoic acid.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers.

Lesson plan overview

Introduction

1. The teacher hands out Methodology Guide or green, yellow and red sheets of paper to the students to be used during the work based on a traffic light technique. He presents the aims of the lesson in the student's language on a multimedia presentation and discusses the criteria of success (aims of the lesson and success criteria can be send to students via e‑mail or posted on Facebook, so that students will be able to manage their portfolio).

2. The teacher together with the students determines the topic – based on the previously presented lesson aims – and then writes it on the interactive whiteboard/blackboard. Students write the topic in the notebook.

3. Health and safety – before starting the experiments, students familiarise themselves with the safety data sheets of the substances that will be used during the lesson. The teacher points out the need to be careful when working with them.

Realization

1. The teacher introduces students to the issue of ethanoic acid (acetic acid). Referring to its occurrence and application, it displays on the multimedia board an illustration of the abstract food label and encourages students to discuss.

2. The teacher divides the students into groups. He distributes the ball models to them and instructs them to build a model of ethanoic acid based on the homologous series of carboxylic acids.

3. Students work in the same groups. Their task is to design their own experiment, referring to the following research problem: „Is acetic acid soluble in water?”. The experimental instruction and hypothesis are written in the form. Leaders in the class forum compare the results of their group's work with the instructions in the abstract (experiment 1). The teacher discusses the ideas of all teams.

4. The teacher asks pupils to run experiment 1, gives them the appropriate equipment, glass and reagents. After completing the task, students in the form record observations and conclusions. The teacher puts them under discussion.

5. The teacher instructs the pupils to read the fragment entitled „Chemical properties of acetic acid”. Students, working in pairs, mutually question each other from the knowledge of the fragment.

6. The teacher informs students that they will work in groups again. As before, their task will be to design an experiment and compare their ideas with the instructions in the abstract. Part of the class performs the task, referring to the research problem: „Does acetic acid react with metals?” (Experiment 2), others study the problem: „Does acetic acid react the oxides of metals?” (Experiment 3). Everyone saves the hypothesis and the ideas developed in the group in the abstract form. After the appointed time, the teacher displays a movie titled „The effects of ethanoic acid”, showing the correct course of both experiments. Students note their observations and conclusions, evaluate the correctness of their instructions. The leaders successively present the results of their teams' work, the teacher discusses them and provides feedback.

7. The teacher introduces students to the issue of formic acid. Referring to its occurrence and application, it displays on the multimedia board an illustration of the abstract food label and encourages students to discuss. Together with students, it analyzes the pattern of electrolytic dissociation reactions and formulas for the reaction of formic acid with metals, metal oxides and hydroxides (in abstract).

8. The teacher asks students to summarize the information about acetic acid and formic acid. He also asks for interactive exercises in the abstract.

Summary

1. The student indicated by the teacher sums up the lesson, telling what he has learned and what skills he/she has been practicing.

2. The teacher chooses one student by random method and asks him or her to explain in own words the meaning of a given word or concept learned during the lesson.

Homework

1. Listen to the abstract recording at home. Pay attention to pronunciation, accent and intonation. Learn to pronounce the words learned during the lesson.

2. Make at home a note from the lesson using the sketchnoting method.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Carboxylic acids – properties

Vinegar is used in the kitchen as a condiment or food preservative. Surely you know its sour taste. The label tells us that vinegar is a 10% aqueous solution of acetic acid. Anhydrous acetic acid at temperatures below 16°C takes the form of colourless mass. It looks like ice – hence the name glacial acid. Acetic acid, as a product of sour wine, has accompanied man since ancient times.

Testing acetic acid, we will answer the following questions: What are the chemical properties of lower carboxylic acids? Do they react with metals and their oxides like inorganic acids? What effect does the presence of the carboxylic group have on their reaction? Do indicators in aqueous solutions of organic acids change colour just like in aqueous solutions of inorganic acids?

What properties of acetic acid can we read from pictograms?

Pictograms tell us that concentrated acetic acid is a flammable substance. It causes skin and eye burns. Due to the dangers, no concentrated acetic acid solution is stored in the school's chemical workshop. For experiments, we use only an acetic acid solution whose concentration does not exceed 10%.

Acetic acid is easily recognizable by its sharp, characteristic odour. This is why we should try to close the acid bottle quickly and tightly.

Write down the hypothesis and instructions for each experiment. Write down observations and conclusions. After completing the experiments, watch the video.

Watch the video and look how the two experiments took place.

Methanoic acid HCOOH, commonly known as formic acid, is a representative of carboxylic acids. The substance is liquid, colorless, has a strong odor and is well soluble in water.

What properties of formic acid can we read from the pictogram?

It causes severe skin burns and eye damage. It is volatile and its vapors irritate the mucous membranes.

Aqueous solutions of acetic and formic acids are electrically conductive and produce a red coloring of the red cabbage juice. Thus, the electrolytic dissociation reaction takes place:

$\text{HCOOH}\stackrel{{\text{H}}_{\text{2}}\text{O}}{\to }\text{HCO}{\text{O}}^{-}\text{ + }{\text{H}}^{\text{+}}$

$\text{formic acid → anion of acid radicals (formic) + hydrogen cation}$

The salts of formic acid are called formates. They are produced by the reaction of formic acid with metals, metal oxides and hydroxides:

$\text{2HCOOH}\text{+ }\text{2Na}\text{ → }\text{2H}\text{COONa}\text{ +}{\text{ H}}_{\text{2}}\text{↑}$

$\text{formic acid + sodium → sodium formate (sodium methanoate) + hydrogen}$

$\text{2HCOOH }\text{+ }\text{CuO}\text{ → (}\text{HCOO}{\text{)}}_{\text{2}}\text{Cu}\text{ + }{\text{H}}_{\text{2}}\text{O}$

$\text{formic acid + copper(II) oxide → copper(II) formate (copper(II) methanoate) + water}$

$\text{2HCOOH }\text{+ }\text{Ca}\text{(}\text{OH}{\text{)}}_{\text{2 }}\text{→ (}\text{HCOO}{\text{)}}_{\text{2}}\text{Ca}\text{ + }\text{2}{\text{H}}_{\text{2}}\text{O}$

$\text{formic acid + calcium hydroxide → calcium formate (calcium methanoate) + water}$

• Pure acetic acid is a colourless, corrosive liquid. It is hygroscopic (it absorbs moisture from the air).

• At temperatures below 16°C, it forms crystals that resemble ice in appearance. It is also called glacial acetic acid.

• Acetic and formic acids dissolve well in water.

• The reaction of aqueous solutions of carboxylic acids that have short carbon chains, and the electrical conductivity, are evidence of electrolytic dissociation.

• Carboxylic acids react with hydroxides, metals and metal oxides, to form salts.