Topic: Solutions

Supplementary material for use in lessons in the group of natural sciences (nature, biology, chemistry, geography, physics), additional classes, science clubs. It can serve as a resource for expanding knowledge, preparing students for science competitions.

Target group

7th‑grade students of elementary school

Core curriculum

7th‑grande of elementary school – chemistry

V. Water and aqueous solutions. Student:

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;

4) designs and conducts experiments showing the influence of various factors on the dissolution rate of solid substances in water.

General aim of education

The students examine experimentally the factors affecting the dissolution of the substance.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• prepare solutions;

• indicate factors that can affect the dissolution process;

• explain what properties of water make it extremely important for human life and health.

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;

• interactive whiteboard, tablets/computers;

• substances and objects needed to carry out „Observation 1”: hot water; cold water; crystal sugar; powdered sugar; teaspoon; six glasses.

Lesson plan overview

Before classes

• Students get acquainted with the content of the abstract. They prepare to work on the lesson in such a way to be able to summarize the material read in their own words and solve the tasks themselves.

Introduction

• The teacher explains the aim of the lesson and together with students determines the success criteria to be achieved.

• The teacher, referring to the knowledge acquired by students in previous classes, asks for clarification of what a mixture is. Volunteers define this concept and then exchange examples of homogenous and heterogeneous mixtures.

Realization

• The teacher instructs students to read the first part of the abstract themselves and explain what the solution is.

• The teacher asks the pupils to remind them of the principles of safe observation.

• Students in pairs perform observations in accordance with the instructions in the abstract („Observation 1”), and write their conclusions on the factors affecting the dissolution of substances in notebooks.

• Participants familiarize themselves with the content presented in the interactive illustration. Then the teacher discusses the issues with the students.

• The teacher asks pupils to explain why we usually deal with aqueous solutions every day.

Summary

• Students independently perform interactive exercises.

Homework

• Develop a lap book containing issues learned during the lesson and bring your work to the next class.

• 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

Solutions

When creating a mixture sometimes the particles of one substance are dispersed in another. Such process is called dissolution. If one substance completely dissolves in the other substance, a homogeneous mixture called a solution is created. Each solution is composed of a solvent and a solute (one or more). A solvent is an ingredient of a solution that is greater in volume and has solute particles evenly dispersed between its own particles.

Examples of solutions include:

• sugar water – water is a solvent in this solution, whereas sugar is the solute;

• sea water – water is a solvent in this solution, mineral salts and other components are solutes;

• sparkling mineral water – it’s an example of a multi‑component solution in which mineral salts (solids) and carbon dioxide (gas) are dissolved in water;

• Vinegar – water is a solvent in this solution, whereas acetic acid is a solute.

On a day‑to‑day basis, we most often deal with solutions in which the solvent is water, i.e. aqueous solutions. More substances can be dissolved in water than in any other known solvent. Aqueous solutions that occur in nature contain dissolved solids, liquids or gases. Plants draw water along with mineral salts they need to survive dissolved in that water from the soil. The same applies to humans and animals – necessary substances are delivered to our organisms along with an aqueous solution.

Can we dissolve any volume of sugar or salt in water? In order to check that, it’s best to perform an experiment. We’ll examine the solubility of substances and the factors that affect it.

It’s necessary to remember that some substances are not soluble in water, but may be perfectly soluble in other substances. As solvents we’ll use gasoline or alcohol, among others.

• Solutions are homogeneous mixtures composed of two or more substances. They contain a solvent and a solute dissolved in that solvent. Aqueous solutions of substances are the most common.

• The dissolution process is affected by: temperature of the solvent, the stirring of components and decreasing the size of solute particles.