Topic: Dilution and cooling of solutions

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Elementary school. Chemistry.

V. Water and aqueous solutions. Student:

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 using the solubility plot

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• calculate the percentage concentration of a saturated solution at a set temperature;

• determine the solution solubility based on the percentage of saturated solution at a given temperature.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

• exposing

  • exposition.

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.

3. Health and safety - before starting experiments, the teacher acquaints students with the characteristics of the substances that will be used in the lesson. He indicates the need to be careful when working with them.

Realization

1. The teacher discusses calculations used in the preparation of saturated solutions from dilute solutions at a given percentage concentration.

2. The lecturer translates tasks of a different type - dilution of saturated solutions to obtain a solution with a given percentage concentration. Presents another exercise from the abstract, discussing how to solve it.

3. The teacher discusses tasks related to cooling the saturated solution.

4. The teacher refers students to the abstract. Displays on the board successively exercise 4, then 5, each of them discussing and discussing with students.

5. The teacher refers to the situations of mixing of two solutions with other percent concentrations known from everyday life, resulting in a new solution with yet another concentration. Appeals students to the abstract. Displays exercise 6, discussing them and discussing them with students.

6. The teacher, referring to the situation of mixing solutions with different concentrations, refers to the so‑called rules of St. Andrew (also called the square of dilutions, the rule of mixing, the rule of the cross). Familiarize students with animation presenting a stepwise solution of the task for calculating the percentage by the cross‑method.

7. Students perform interactive exercises described in the methodical commentary - work in pairs.

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

2. The teacher briefly presents the most important issues discussed in class. He answers the additional questions of the proteges and explains all their doubts.

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

Dilution and cooling of solutions

Concentration solutions may be obtained from dilute solutions, e.g. by evaporation of the solvent. When saturation is reached, further concentration of the solution will lead to the evaporation of solute from the solution.

The solubility of solids in water generally increases with increasing temperature, and decreases as temperature decreases. For this reason, when the saturated solution is cooled, a portion of the solute is isolated as a precipitate. Knowing the solubility of substances at two different temperatures, one can determine the amount of substance that will be released during cooling of any mass of saturated solution.

• Based on the knowledge of the solubility of the substance, the percentage of saturated solution can be calculated.

• Knowing the percentage concentration of a saturated solution of a substance, you can calculate its solubility.