Topic: Hydroxides – properties and application

Target group

Elementary school student (grades 7. and 8.)

Core curriculum
An eight‑year elementary school
VI. Hydroxides and acids. Pupil:
3) describes the properties and resulting applications of some hydroxides and acids (e.g., NaOH, Ca(OH)Indeks dolny 2₂, HCl, HIndeks dolny 2₂SOIndeks dolny 4₄).

General aim of education

The student describes the properties and resulting applications of some hydroxides.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• what are the most important properties of sodium, potassium and calcium hydroxides;

• give examples of hydroxides that can be called bases based on the solubility table;

• use the solubility table;

• describe the use of some hydroxides.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers;

• sheets of gray paper;

• colored markers.

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 the students to the issue implemented during the lesson and announces a movie titled „Testing the properties of sodium and potassium hydroxides”. 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.

2. The teacher asks the class participants to read the experiment's instructions in the abstract (Experiment 1: “Testing the properties of calcium and iron(III) hydroxides”). The teacher divides students into groups and distributes appropriate equipment, glass and reagents to perform the experiment. Students - with the help of the teacher - formulate a hypothesis and a research question and write them on the form in the abstract. Then they follow the instructions. They record the observations in the form. The teacher asks questions in relation to the observations noted. He initiates a discussion, the conclusions of which students write on the form.

3. Referring to the solubility of hydroxides, the teacher instructs students to analyze the solubility table of hydroxides' solubility in water in the abstract.

4. The teacher divides the students into three groups. Each one deals with a different issue: 1st group - application of sodium hydroxide, group II - application of potassium hydroxide, group III - application of calcium hydroxide. Students show the effects of their work in graphic form on sheets of paper or using the sketchbook in the abstract. After the end of the activities, the group leaders present team‑formed infographics.

5. The students carry out an interactive exercise. The teacher makes sure that the task have been correctly completed and gives feedback.

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.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Hydroxides – properties and application

A laboratory vessel serving, among others for storage of hygroscopic substances is a desiccator.

Its cover is made of thick glass or plastic and adheres closely to the container in which there is a drying substance (e.g., potassium hydroxide). Some desiccators are equipped with a tap for removing air.

Hydroxides are solids that can have different colours. Sodium and potassium hydroxides and hydroxides of other elements from the 1st group of the periodic table are very soluble in water. The solubility of the hydroxides of the 2nd group increases with the increase of the atomic number of the alkaline earth metals, and the hydroxides of the remaining metals are practically insoluble in water. Using the solubility table of hydroxides, it can be checked which of these are soluble in water and which precipitate in the form of sediments, i.e. are practically insoluble in water.

Concentrated solutions of sodium, potassium (formerly corrosive alkalises) and calcium hydroxides have caustic properties – destroy the paper. These work similarly on the skin – can cause severe burns. Molten sodium hydroxide damages (digest) glass, so it is stored in plastic packaging.

Sodium and potassium hydroxides form water‑soluble compounds with fats, which is why these are used as components of preparations for agents unblocking pipes as well as for the production of washing agents. Calcium hydroxide forms a suspension with water – cream of lime. It is used for limewashing the fruit trees and building walls, because it has disinfecting properties, while white colour reflects a significant part of the sun's rays and prevents excessive heating. A clear colourless solution of calcium hydroxide is called lime water. It is used to detect carbon dioxide.

Lime mortar
The constituent of the lime mortar is, in addition to sand and water, slaked lime, which is formed in the reaction of quicklime with water. The prepared dough‑like mixture has the ability to harden due to the chemical reaction of calcium hydroxide with carbon dioxide from the air.

• Hydroxides are solid substances of different colour.

• Sodium and potassium hydroxides are highly hygroscopic substances, have similar properties, are used as ingredients for the production of soaps, detergents and preparations for the pipes unblocking agents.

• Concentrated solutions of sodium, potassium and calcium hydroxides have corrosive properties.

• Magnesium and aluminium hydroxides are among others components of antacids.