Topic: Carboxylic acids – structure

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

IX. Hydrocarbon derivatives. Pupil:

4. gives examples of organic acids found in nature (eg formic acid, oxalic acid, citric acid) and lists their uses; draws the semi‑structural (group) and structural formulas of simple‑chain monocarboxylic acids with up to five carbon atoms and gives their common and systematic names.

General aim of education

The student creates a series of homologs of straight‑chain monocarboxylic acids containing up to five carbon atoms per molecule, and gives their common and systematic names.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to construct models of carboxylic acid molecules;

• to write down the molecular and structural formulas of simple carboxylic acids;

• to create the names of carboxylic acids.

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 carboxylic acids, referring to the acetic fermentation process that occurs during the acidification of alcoholic beverages, e.g. beer - discussion is under way. It guides students to examples of acids known to them from everyday life, such as oxalic, lemon, and lactic acid. Then, he writes the equation of the acetic fermentation reaction on the board, explains its mechanism.

2. The teacher discusses the presence of formic acid. He gives ball pupils to students and asks them to execute a 2 command from the abstract (working in pairs). Presents - to check the correctness of the command implementation by students - a film from the abstract „Modeling the formic acid molecule” and formic acid formulas: total, group, structural.

3. After introducing students to the subject of carboxylic acids by discussing the structure of acetic and formic acid, the teacher gives the general formula for a series of homologous carboxylic acids. He asks those who want to approach the array and write on it the homologous series of carboxylic acids from 1 to 5 carbon atoms in the acid molecule (record of the summary, group and structural formula as well as the systematic and customary name).

4. The teacher displays on the board „Formulas of oxalic and lactic acid”, using the resource in abstract.

5. In order to consolidate the message and skills, the teacher asks students to do interactive exercises in the abstract.

Summary

1. The teacher plays the recording of the abstract. Every now and then he stops it, asking the students to tell in their own words what they have just heard.This way, the consolidate information learned during the lesson students practice listening comprehension.

2. The teacher asks a willing student to summarize the lesson from his point of view. He asks other students if they would like to add anything to their colleague's statements.

Homework

1. Carry out task number 3.1.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Carboxylic acids – structure

When wine goes bad, ethyl alcohol is converted into ethanoic acid. This reaction takes place in presence of oxygen and enzymes produced by acetic bacteria. This process is called acetic fermentation.

Chemical equation – denoted with words:

$\text{ etanol }+\text{ oxygen }\stackrel{\text{ enzymes }}{⟶}\text{ ethanoic acid }+\text{ water }$

Chemical equation – molecular equation:

${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}+{\mathrm{O}}_2\stackrel{\text{ enzymes }}{⟶}{\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{H}}_2\mathrm{O}$

The following can be concluded from the chemical equation:
In presence of oxygen and enzymes ethyl alcohol undergoes a chemical reaction the products of which are ethanoic acid and water.

Ethanoic acid consists of the same number of carbon atoms as ethane. This substance is classified as ethane derivative as their composition is similar. That is why its systematic name is ethanoic acid.

In the ethanoic acid molecule carbon atoms are linked together with a single bond. One oxygen atom forms a double bond with a carbon atom. The second oxygen atom forms one bond with a hydrogen atom and the other one with a carbon atom. The remaining hydrogen atoms are fixed with carbon with a single bonds.

Molecular formula of ethanoic acid allows us to name the types and number of individual atoms. But we will not be able to find out how are these atoms bonded in the molecule. It is the structural formula that gives information about the number of bonds between individual atoms.

Methanoic acid is present in venom of ants which use it to destroy parasites. The same acid is produced for example by bees and nettle – a well known plant that stings. When we touch a nettle we will immediately feel burning and pricking and, develop itchy blisters on our skin. This is because on the leaves there are present small plant hairs (trichomes) which inject the irritant formic acid under the skin.

Methanoic acid is believed to be a derivative of methane. It contains one carbon atom in a molecule.

Carboxylic acids are hydrocarbon derivatives in which hydrogen atom (or atoms) is (are) substituted with a functional carboxyl group $\text{–}\text{C}\text{O}\text{O}\text{H}$. Carboxylic acids are classified according to the number of carbon atoms into lower ones – with smaller number of carbon atoms, and higher ones – with several carbon atoms in a molecule. Methanoic and ethanoic acids are lower acids.

$\text{–}\text{C}\text{O}\text{O}\text{H}$ – a group typical of carboxylic acids is bonded with a hydrocarbon group. A group of atoms bonded with a hydrocarbon chain will be called a functional group.
Thus $\text{–}\text{C}\text{O}\text{O}\text{H}$ group is a functional group of organic acids.

Organic acids with a carboxyl group are called carboxylic acids.
Like hydrocarbons, organic acids with one carboxyl group in a molecule form a homologous series. The systematic names of carboxylic acids consist of two parts. In order to create the systematic name, the name of alkane with the same number of carbon atoms in a molecule to the word „acid”, adding the ending -oic; for example methanoic acid, ethanoic acid. It should be noted that common names are usually used in practice. Common names are associated with the occurrence of acids. Formic (methanoic) acid is found in ant venom, butyric (butanoic) acid – in rancid butter, and lactic acid – in some dairy products.

Table 1. shows acids listed according to the number of carbon atoms in a molecule. Each subsequent molecule differs from the previous one in $\text{–}\text{C}{\text{H}}_{\text{2}}\text{–}$ group. This series is called a homologous series of carboxylic acids.

Table 1. Names and formulas of selected carboxylic acids.

If the carboxylic acid is an alkane derivative and contains one carboxyl, its generalized formula is as follows:

${{\text{C}}_{\text{n}}\text{H}}_{\text{2n+1}}\text{C}\text{O}\text{O}\text{H}$

The general formula of monocarboxylic acids derived from alkanes.

Organic acids make contain several carboxyl groups in their molecules (for example oxalic acid) and other functional groups such as a hydroxyl group (for example lactic acid).

• Ethanoic acid is one of the products of acetic fermentation. Diluted alcoholic beverages undergo this process.

• Carboxyl group $\text{–C}\text{O}\text{O}\text{H}$ is a functional group of carboxylic acids.

• Carbxylic acids are hydrocarbon derivatives which contain at least one carboxyl group.

• Methanoic and ethanoic acids classified as lower carboxylic acids.