Topic: Hydroxides - structure and identification using indicators

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Elementary school. Chemistry.

VI. Hydroxides and acids. Pupil:

1) recognizes formulas of hydroxides and acids; writes the sumaric formula of the hydroxides: NaOH, KOH, Ca(OH)Indeks dolny 2₂, Al(OH)Indeks dolny 3₃, Cu(OH)Indeks dolny 2₂ and acids: HCl, HIndeks dolny 2₂S, HNOIndeks dolny 3₃, HIndeks dolny 2₂SOIndeks dolny 3₃, HIndeks dolny 2₂SOIndeks dolny 4₄, HIndeks dolny 2₂COIndeks dolny 3₃, HIndeks dolny 3₃POIndeks dolny 4₄ and name them;
5) indicates the use of indicators, e.g. phenolphthalein, methyl orange, a universal indicator paper; distinguish experimentally with solutions of acids and hydroxides using indicators.

General aim of education

The student discusses the structure of hydroxides and identifies hydroxide solutions using indicators

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• what is hydroxide;

• to name hydroxides based on their formulas;

• to list and describe the methods for obtaining hydroxides and write the corresponding reaction equations;

• to give examples of metals and metal oxides reacting with water;

• to identify reaction products of active metals with water;

• to give examples of acid‑base indicators and determine their color in water and in principles.

Methods/techniques

• expository

  • talk.

• activating

  • discussion;

  • snowball method.

• 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;

• stiletto‑ball models.

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. A reminder of the information about the atom's structure: H, Na, K, O, Mg, Ca, Al, Cu - work with the periodic table of elements. The teacher asks students questions about the elements in relation to their position in the group, period, chemical activity, the number of electrons on the last shell.

2. The teacher writes on the board the NaOH formula - in relation to the valence of the translators, how the sum formula of such a chemical is determined, how the name is created and writes the structural formula. Then he displays tables with names and valences of metals. He explains how the name hydroxide is formed in the case of an element that has one and several valences.

3. The teacher divides the students into groups. Disposes rod‑ball models. Each group receives 3 total formula hydroxides. Their task is to write the names of compounds, structural patterns and build models. During work, the teacher, if necessary, provides explanations. After the expiration of the appointed time, the groups present their work.

4. Students in pairs work with the snowball method. Their task is to create a general pattern of hydroxides. Then they join in fours, compare their proposals, verify them and set a common position. In the next steps, the students join in more numerous groups and set a common version of the design, until a general class position is agreed.

5. The teacher announces a movie. He instructs his pupils to write a research question and a hypothesis in the form provided in the abstract. Then he plays the video and the students note their observations and conclusions. The teacher points the person who shares his insights and explains the reasonableness of the conclusions noted.

6. Students perform interactive exercises from the abstract.

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

Hydroxides - structure and identification using indicators

Hydroxides are chemical compounds with a constant state of aggregation, made of metal cations and hydroxide anions.
These ions are attracted by the action of electrostatic forces, creating crystal structure.

The valency of the hydroxyl ions always equals I.

The general formula of monovalent metal hydroxides:

The general formula of metal hydroxides:

Hydroxide names are created by adding to the name of the element that forms the compound the word “hydroxide”:

If the metal forms two hydroxides, the Roman numeral in parentheses is added to the name, indicating the valency of the metal, for example:

If the metal forms one hydroxide, the valency of the metal in the name is omitted:

The fact that the studied compounds have different properties can be seen using substances called indicators. Their action under the influence of other substances depends on the fact that they change the color in an easy to observe way. This allows us to determine whether the sample is the substance interesting for us.

In everyday life we also find indicators. Tea, to which we add lemon juice, changes its color to lighter. Similarly, when we add lemon juice (citric acid) or vinegar (acetic acid) to beetroot juice, the dye in this juice under the influence of acids will take on an intense red color.

An indicator changing colour in water solutions, to which we add metals and metal oxides (with the creation of a new chemical compound – hydroxide) is, among others, decoction of red cabbage.

An indicator or an indicating dye is a substance with which we can detect another substance, e.g. as a result of a change in color.

• Hydroxides are chemical compounds made of metal cations and hydroxide anions whose general formula is ${\text{M(OH)}}_{\text{n}}$.

• Hydroxides are obtained as an effect of the reaction of active metal oxides (basic oxides) with water and of some metals with water.

• Solutions of hydroxides that are easily soluble in water (all hydroxides of metals from the 1st group of the periodic table and selected metals from the 2nd group) are traditionally called bases.