Topic: Percent concentration of the solution - definition

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 interprets the percentage concentration of the solution

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 calculate the percentage concentration of a solution based on its mass or mass of solvent and mass of solute;

• to estimate the mass of the solution based on the percentage of solution and the mass of solute;

• to determine the mass of solute based on the percentage and mass of the solution.

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.

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, introducing students to the problem of the percentage concentration of the solution, gives some examples of its significance, referring to the industry. It informs that in chemical laboratories and in everyday life, solutions with a certain content of substances in their given amount, i.e. known concentration, are used. One of the ways of expressing concentration of solutions is the percentage concentration.

2. The lecturer displays an illustration of „Every day we meet the articles on which the contents of their ingredients have been provided” from the abstract and analyzes it, interpreting the descriptions.

3. The teacher displays the presentation „How to understand the percentage concentration of the solution?” From the abstract. After projection, he introduces the formula for the percentage concentration of the solution and on the basis of it defines the percentage concentration of the solution - the students write the information in the notebooks. Then he presents the table „Interpretation of a 4‑g solution with 100g weight” on the multimedia board and analyzes it on the forum.

4. The teacher, referring to the calculation of the percentage of the solution, refers the students to the abstract and asks them to view and analyze the instructions for calculating the percentage concentration by definition and using the proportion. He asks a willing student to solve the task on the board.

5. The teacher informs students that knowing the percentage concentration of the solution and its mass, it is possible to calculate the mass of solute. Similarly, the mass of the solution can be determined based on the information on the percentage concentration of the solution and the mass of dissolved substance contained in it. The calculation uses both the appropriate proportion and the converted formula for the percentage concentration. On the basis of the next abstract command, the teacher explains to the students how to make calculations using the proportions. With regard to the next command, he asks you to make calculations of this task.

6. The lecturer asks you to do an interactive exercise (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

Percent concentration of the solution - definition

The terms „concentrated solution”, „diluted solution” or „saturated solution” only indicate the amount of the given solute is in solution. Sometimes it is necessary to provide its exact content. There are several ways to present the composition of the solution, i.e. its concentration.

One of them is percent concentration. It determines how many parts of the mass (in weight) of dissolved substance is found in 100 parts of the mass (in weight) of solution. A 5% means that there are 5 grams of solute in 100 grams of solution.

The percent concentration can be calculated using the formula: ${\text{C}}_{\text{p}}\text{=}\frac{{\text{m}}_{\text{s}}}{{\text{m}}_{\text{r}}}\text{· 100\%}$

Where following symbols mean:
${\text{C}}_{\text{p}}$ – percent concentration,
${\text{m}}_{\text{s}}$ – mass of the substance,
${\text{m}}_r$ – mass of the solution.

Recall that the mass of the aqueous solution (${\text{m}}_r$) is the sum of the mass of the solvent (${\text{m}}_{\text{solv.}}$), usually water and mass of the solute (${\text{m}}_{\text{s}}$):

${{\text{m}}_{\text{r}}\text{= m}}_{\text{solv.}}\text{+}{\text{m}}_{\text{s}}$

If we know the mass of the solvent or the mass of the solution and the mass of the dissolved substance, we can determine the percent concentration of the solution. In all calculations we must remember about the mass units that we always insert into the formula.

Knowing the percent concentration of the solution and its mass, the mass of solute can be calculated. Similarly, we can determine the mass of the solution based on the information on the percent concentration of the solution and the mass of the dissolved substance contained in it. Both right proportion and appropriately converted formula for the percent concentration can be used in the calculations.

cIndeks dolny p_p – percent concentration
mIndeks dolny s_s – mass of substance
mIndeks dolny r_r – mass of solution

• Percent concentration is the information about how many parts of the mass (in weight) of the dissolved substance are found in 100 parts of the mass (in weight) of the solution.

• The percent concentration of a solution can be calculated based on the weight of the solution and the weight of the solute, using the formula: ${\text{c}}_{\text{p}}\text{=}\frac{{\text{m}}_{\text{s}}}{{\text{m}}_{\text{r}}}\text{· 100\%}$.

• The mass of solute can be calculated based on the percent concentration and mass of the solution: ${\text{m}}_{\text{s}}\text{=}\frac{{\text{c}}_{\text{p}}·{\text{m}}_{\text{r}}}{\text{100\%}}$.

• The percent concentration of the solution can be calculated based on the weight of the solvent and the weight of the solute, using the formula: ${\text{c}}_{\text{p}}\text{=}\frac{{\text{m}}_{\text{s}}}{{\text{m}}_{\text{solv.}}\text{+}{\text{m}}_{\text{s}}}\text{· 100\%}$.

• If the density of the solution is known, it is possible to determine the mass of given volume.