Topic: Changing the concentration of the solution– dilution

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Elementary school. Chemistry.

V. Water and aqueous solutions. Pupil:

7) performs calculations using the following notions: solubility, percent concentration (mass percentage), mass of substance, solvent mass, mass of solution, solution density (using solubility table or solubility plot).

General aim of education

The student calculates the percentage concentration of solutions after dilution

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:

• calculate the percentage concentration of the dilution solution.

Methods/techniques

• expository

  • talk.

• activating

  • discussion;

  • brainstorming.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• activity in pairs;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• projector;

• interactive whiteboard, tablets/computers;

• methodician or green, yellow and red cards.

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. When introducing students to dilution of solution concentrations, the teacher asks the questions: What does the term „dilution” mean? What substances do you know that should be diluted? Students give their suggestions during a brainstorming session, the moderator writes them on the board. After the creative phase, ideas are verified. The teacher supplements the information if necessary. At the end, ask the willing/selected student for a summary.

2. The teacher displays on the multimedia board an illustration of „Model of solution dilution process” from the abstract. Students discuss the process. The teacher asks if the students know another way to dilute the solution. He asks guiding questions on the method of removing a solute. If necessary, supplement information or explain the phenomenon.

3. The teacher displays a presentation showing the stepwise solution of the task for calculating the concentration after dilution. He discusses each stage with his students, and at the end he asks students to determine the level of understanding of the material using Methodology Guide.

4. The teacher asks the willing/selected student to solve exercise 1 from the abstract on the board. If necessary, the teacher gives explanations.

5. The students, working in pairs, solve the other exercises. Each of them is discussed in forms of the class.

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

Changing the concentration of the solution– dilution

During many activities related to work, research or everyday life, we add water or other solvent to various liquids (substance solutions). The process that we then cause is called dilution. As a result, we increase the amount (mass) of the solvent, whereas the amount (mass) of the solute does not change.
What happens with the concentration percentage of the diluted solution?

When adding a further portion of solvent to the solution, the number of solvent particles per diluted solute particles increases. Thus, the mass of solvent relative to the mass of solute increases.

Another possible way to dilute the solution is removing the solute.

This treatment is quite difficult to make and is only possible with concentrated solutions.

It consists of cooling the solution to a temperature at which solubility of the solute is low enough that the substance is released from the solution. After removal of the separated substance, the solution contains less of it and its percentage is lower than the original one.

• Concentration of the solution can be changed by dilution.

• As a result of dilution, the concentration of the solution decreases.

• The solution can be diluted by adding a solvent to it.