Topic: Water and its properties - dissolution processes and types of mixtures

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

V. Water and aqueous solutions. Pupil:

2) give examples of substances that do not dissolve in water, and examples of substances that dissolve in water, forming solutions; gives examples of substances that form colloids and suspensions with water;

3) designs and conducts experiments on the solubility of various substances in water.

General aim of education

The student discusses the types of solutions due to the size of molecules of the dissolved substance in water.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• present the interactions between water molecules;

• define molecular dispersion, colloidal suspension and suspension.

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.

Realization

1. The teacher conducts a discussion about the structure of the water molecule (to remind the reader). He asks students to think about why some substances dissolve in water and others do not. Students give answers, the teacher assesses their accuracy.

2. The teacher indicates that not all substances dissolve well in water. Some of them are not affected by the disintegration of individual particles, but they form larger clusters. Instructs students to arrange a picture (puzzle) in the abstract, which initiates discussing the types of mixtures depending on the size of the particles. The teacher also presents an abstract infographic on this subject („Division of mixtures due to the particle size of the substance dissolved in the liquid (water)”).

3. The teacher announces a movie titled „How to distinguish between the molecular dispersion, colloidal suspension and suspension”. He instructs his students 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.

4. Students, by brainstorming, define molecular dispersion, colloidal suspension and suspension. The teacher assesses the accuracy of the proposed terms - the students write them in the form in an abstract.

5. Students, working individually or in pairs, carry out interactive exercises to check and consolidate knowledge learned during the lesson. Selected people discuss the correct solutions for interactive exercises. The teacher completes or straightens the statements of the proteges.

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

Water and its properties - dissolution processes and types of mixtures

Water is the most widespread solvent in nature as well as in laboratories.
Many substances that form molecular dispersions in water undergo various processes during dissolving.

Water dissolves substances that are also polar. In addition, it dissolves most ionic compounds very well. Polar covalent compounds may behave differently in water: some of them remain as molecules (e.g. sucrose), while others may be broken down into ions (e.g. hydrogen chloride). Ionic compounds, if dissolved in water, are broken up during mixing, and ions from the crystal lattice are transferred into solution.

Not all substances dissolve well in water and form the molecular dispersions. Some of them are not subject to decomposition by water to individual particles, but these form larger clusters in the water. Depending on the size of the resulting particles, their mixtures with water have different names: colloid (colloidal suspension) or suspension.

Homogeneous mixture:

• Homogeneous mixture - particle size less than 1 nm (10Indeks górny -9^-9m)

Heterogeneous mixture:

• Colloid (colloidal solution) - the particle size ranges from 1 nm to 200 nm (10Indeks górny -9^-9m – 200 · 10Indeks górny -9^-9m)

• Suspension - particle size bigger than 200 nm (200 · 10Indeks górny -9^-9m)

• Water is a polar substance. There is a negative charge on the oxygen atom, on hydrogen atoms – positive.

• Water creates mixtures with various substances. Depending on the size of the resulting particles, their mixtures with water have different names: colloid (colloidal suspension) or suspension.

• In the molecular dispersions, we distinguish the solvent, which is superior to the solute.

• Water dissolves substances that are also polar. It also dissolves most of the ionic compounds.