Topic: Solubility of substances - solubility and solubility curves

Target group

Elementary school student (grades 7. and 8.)

Core curriculum

Elementary school. Chemistry.

V. Water and aqueous solutions. Pupil:

5) defines the term solubility; gives the difference between saturated and unsaturated solution;
6) reads the solubility of substances from the solubility table or from the solubility plot; calculates the mass of the substance that can be dissolved in a given amount of water at the given temperature.

General aim of education

The student explains the concept of solubility and interprets the solubility curves to determine the solubility of the substance

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:

• to interpret solubility curves to determine the solubility of a substance;

• to distinguish the terms: saturated solution, unsaturated solution and dilute solution and concentrated solution;

• to describe changes in solubility of solids and gases in water depending on temperature.

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;

• projector;

• interactive whiteboard, tablets/computers;

• methodician or green, yellow and red cards;

• equipment, laboratory glass and reagents for observation - see description of the experiment in the methodical commentary.

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 reminds the students that the concept of solubility appeared in the previous lesson. However, it has not been precisely defined yet and this will happen in this class. He emphasizes that sugar or kitchen salt very well dissolve in water, but not all of them can be dissolved in a glass of water. In order to explain this phenomenon, the teacher presents on the multimedia board the film „Dissolution of rock salt and sugar in a given amount of water and temperature” from the abstract. After the screening, he encourages students to discuss observations, analyze the results obtained during the experiment and inference as well as record (also with prior determination of the research question and hypothesis) information in the observation diary in the abstract. He asks a question to students: „What is solubility? How can you define it by referring to the experiment carried out? „.

2. The teacher asks students to analyze the table „Solubility of various solid substances in grams per 100 g of water depending on temperature” in abstract.

3. The lecturer refers students to the table „Solubility of exemplary gaseous substances in grams per 100 g of water depending on the temperature” in the abstract, asks for its analysis and asks: „How does the solubility of gases and solids in water change with temperature?” talk.

4. The teacher, referring to the previously presented film „Dissolution of rock salt and sugar in a given amount of water and temperature” from the abstract, refers to the table with the results of the mass of beakers with solutions depending on the temperature. It indicates that the higher the temperature of the solution, the more you can dissolve the substance in the same amount of water. Solubility results can be used and marked on the graph - combining them together, you can plot the so‑called solubility curve. At this point, the teacher displays on the presentation a graph of solubility curves of solids using the abstract - the illustration „Solubility curves of exemplary solid substances” and explains the way of reading from the graph. Next, it displays a movie from an external resource on a multimedia board, eg from the Scholaris portal, concerning the solubility curves and the effect of temperature on solubility „- students view and analyze the material contained in it. Thanks to this exercise, they will improve the ability to use the solubility curve and find that each substance has a different temperature‑dependent solubility..

5. The teacher teaches students to abstract and asks for interactive exercises (individual work).

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

Solubility of substances - solubility and solubility curves

Many substances, e.g. methanol, can be dissolved in water in unlimited amounts. There are substances that only dissolve in it to a small extent (e.g., in quantity $\text{1,5 ·}{\text{10}}^{\text{-25}}$g in 100 g water). There are also well‑soluble substances, the amount of which in the solution may exceed four times the mass of water.

The measure of the ability of a substance to dissolve in water is solubility. It defines the maximum amount of substance that can dissolve in a fixed mass or volume of solvent at a given temperature and under constant pressure. In physical and chemical tables, solubility is most often expressed as the number of grams of substance that can be dissolved in 100 g of water at a given temperature and under constant pressure. This data was determined experimentally.

On the basis of numerical data showing the dependence of the solubility of the substance on the temperature, a diagram is made called the solubility curve.

The solubility curve allows you to determine how the solubility of a given substance changes depending on the temperature. It also provides information whether it is a significant change or a small change. From the graph you can also read the amount of substance that can dissolve up to 100 g of water.

• Different amounts of various substances dissolve in the same volume of water.

• The amount of solid dissolved in water depends on the temperature and usually grows with its increase.

• As the temperature rises, the amount of gas dissolved in the water decreases.

• The maximum amount of substance that can dissolve in a fixed mass or volume of solvent at a given temperature and under constant pressure is called solubility. It can be expressed as the number of grams of substance that can be dissolved in 100 g of solvent at a given temperature and under constant pressure.

• The graph showing the dependence of the solubility of a given substance on the temperature is called the solubility curve.