Topic: Electrolytic dissociation of acids

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Elementary school. Chemistry.

VI. Hydroxides and acids. Pupil: 4) explains what is the electrolytic dissociation of bases and acids; defines the terms: electrolyte and nonelectrolyte; writes the electrolytic dissociation equations of bases and acids (in a stepwise form for $H_{2}S, H_{2}C{O}_3$; defines acids and bases (according to Arrhenius theory); distinguishes the terms: hydroxide and base.

General aim of education

The student explains what electrolytic dissociation of acids is and writes the corresponding equations

Key competences

• communication in the mother tongue;

• communication in foreign languages;

• mathematical competence and basic competences in science and technology;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to explain why aqueous acid solutions conduct electricity;

• to define the concept of acids according to the theory of electrolytic dissociation;

• to write electrolytic dissociation equations of acids and present this process using models.

Methods/techniques

• expository

  • talk.

• activating

  • discussion.

• 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;

• projector;

• interactive whiteboard, tablets/computers;

• methodician or green, yellow and red cards;

• equipment, laboratory glass and reagents for the experiment;

• sheets of paper, markers, glutaki.

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 asks pupils (they can work in groups or in pairs) to plan and carry out an experiment to see if distilled water, carbonated water (a very diluted solution of carbonic acid) and any inorganic acid are conductors of electric current. The form of observations in the abstract are to be used for notes. Finally, the teacher summarizes the issue discussed.

2. By introducing students to the subject of classes, the teacher can use external resources, eg from the Scholaris portal, concerning the dissociation of hydrochloric acid and common electron pairs. He writes the electrolytic dissociation equation of this acid on the board, explains its mechanism, and presents a verbal reading. Students make entries in notebooks.

3. The lecturer may present another external resource, eg from the Scholaris portal, concerning the dissociation of weak acids - he writes on the table the dissociation equation for gradual hydrosulfuric acid, explains its mechanism and presents a verbal reading. Summarizing this stage of the class, it displays the presentation „Dissociation of gradual hydrosulfuric acid” from the abstract on the multimedia board. Students make entries in notebooks.

4. The teacher gives students ball‑and‑ball models and asks for models of the dissociation equation for hydrochloric acid and hydrosulfuric acid - work in pairs.

5. The teacher writes on the board the equation of electrolytic dissociation of nitric acid, explains its mechanism, and presents a verbal reading. Then he displays on the multimedia board „Simplified model scheme of dissociation of nitric acid” from abstract. Students make entries in notebooks.

6. The lecturer asks volunteers to write on the board and present a verbal reading of electrolytic dissociation equations for sulfuric and phosphoric acid. Other students write in notebooks. Next, the teacher recommends showing the course of dissociation of sulfuric acid and phosphoric acid on models and for checking the correctness of task performance displays on the multimedia table simplified model schemes from the abstract, asking for comparison.

7. The teacher displays the next presentation - „Gradual Dissociation of Carbonic Acid” - from the abstract. He asks a willing student to write on the board the equation of this reaction and its verbal reading.

8. The teacher, in reference to the saved and analyzed dissociation equations of electrolytic hydroxides, asks: „How can one show the dissociation of acids by means of the general equation?” - asks to write down the answer on the board and the others to define the concept of principles - refers to the Arrhenius theory.

9. The teacher asks students (individual work) to do interactive exercises.

Summary

1. The teacher asks the students to finish the following sentences:

   • Today I learned ...

   • I understood that …

   • It surprised me …

   • I found out ...

   The teacher can use the interactive whiteboard in the abstract or instruct students to work with it

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

Electrolytic dissociation of acids

One particle of hydrogen sulfide dissociates into two cations of hydrogen ${\text{H3O}}^{\text{+}}$ and one sulfate anion${\text{S}}^{2-}$. This is a reversible process – the molecules break down into ions that can reassemble to form molecules. In the chemical reaction equations, we mark a reversible reaction like this: $\rightleftarrows$.

Hydrogen sulfide in an aqueous solution is not fully dissociated. It means that it contains both ${\text{H}}_{\text{2}}\text{S}$ molecules as ${\text{H}}^{+}$ and ${\text{S}}^{2-}$ ions. Such electrolytes are called weak. For such acids, a double arrow is used $\text{⇄}$.

Hydracids dissociates into: hydronium cations (positive ions) and acid residue anions (negative ions), for example ${\text{Cl}}^{-}$ (chloride anion), ${\text{S}}^{2-}$ (sulfide anion), ${\text{F}}^{-}$ (fluoride anion).

Nitric acid dissociates into oxonium cation and nitrate anion under the influence of water. It should be remembered that both oxonium cations and nitrate anions in an aqueous solution are surrounded by water molecules.

One molecule of sulfuric acid dissociates, i.e. it disintegrates under the influence of water into two hydronium cations and sulfate anion. Both oxonium cations and sulfate anions in an aqueous solution are surrounded by water molecules.

HIndeks dolny 2₂SOIndeks dolny 4₄ + 2 HIndeks dolny 2₂O → SOIndeks dolny 4₄Indeks górny 2-^2- + 2 HIndeks dolny 3₃OIndeks górny +⁺

Oxoacids dissociate into: oxonium cations (positive ions) and anions of the acid residue (negative ions). If necessary, we mark valence of a non‑metal characteristic for a given acid in the name of the anion.

The theory of the disintegration of substances into ions was developed by Svante Arrhenius. According to it acids are chemical compounds that dissociate into oxonium cations and anions of acidic residues in aqueous solution:

${\text{H}}_{\text{n}}\text{R}\stackrel{{\text{H}}_{\text{2}}\text{O}}{\to }{\text{nH}}^{\text{+}}\text{+}{\text{R}}^{n-}$

where:
$\text{R}$ – acid residue,
$\text{n}$ – number of hydrogen atoms in the acid molecule (valency of the acid residue). Charge of the anion of acid residue is equal to the number of cations of oxonium that can be detached from the molecule of an acid.

• Aqueous solutions of acids conduct electricity, because ions are present in their solutions: hydronium cations and anions of acidic residues.

• Hydronium cation is always single‑positive.

• Not all electrolytes are disintegrating into ions equally.

• Strong acids are completely dissociated, while in the weak acid solutions there are also undissociated molecules.