Topic: Soap in the fight for cleanliness - dirt removal mechanism

Target group

High school / technical school student

Core curriculum

New core curriculum:

High school and technical high school – basic level:

XVII. Esters and fats. Pupil:

10) explains what the process of removing dirt is and examines the impact of water hardness on the formation of sparingly soluble compounds; marks hydrophobic and hydrophilic fragments in the molecular formulas of surfactants.

High school and technical high school – extended level:

XVII. Esters and fats. Pupil:

11) explains the dirt removal process; investigates the effect of water hardness on formation sparingly soluble compounds; marks hydrophobic and hydrophilic fragments in formulas surfactant molecules.

Old core curriculum:

High school and technical high school – basic level:

XVII. Esters and fats. Pupil:

10) explains what the process of removing dirt is and examines the impact of water hardness on the formation of sparingly soluble compounds; marks hydrophobic and hydrophilic fragments in the molecular formulas of surfactants.

General aim of education

The student explains the process of removing dirt

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to discuss based on the scheme the mechanism for removing dirt;

• to explain what the process of removing dirt with the use of soap is;

• how to study the effect of water hardness on the formation of sparingly soluble compounds;

• to describe how the hardness of water affects the washing process.

Methods/techniques

• expository

  • talk.

• activating

  • discussion;

  • snowball method.

• 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;

• 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.

Realization

1. The instructor recommends students to familiarize themselves with the experiment's instructions in the abstract. Then on the multimedia board displays the video summarizing the experiment. Students discuss it and try to determine the way in which soap helps get rid of dirt that consists of fat.

2. The teacher divides the class into groups. He asks pupils to analyze the diagram showing the mechanism of removing dirt, in available sources, they sought information on this subject and prepared to discuss it. After completing the task, students present the results of their work: each group discusses one stage of the process of removing dirt.

3. The lecturer writes on the board the question: „What does it mean that the water is hard?”. He asks students to explain this concept. Students work using the snowball method:
   a) first work on the issue in pairs;
   b) then merge into fours and compare their descriptions, review and complete them;
   c) students join in more numerous groups and agree on a common position until a general class description of the phenomenon arises.
   The teacher verifies the students' work and supplements the information if necessary.

4. Next, the teacher displays an interactive diagram with the reaction equations for obtaining calcium and magnesium soaps as insoluble in water. He discusses them together with his students.

5. The teacher and his students discuss the scale of water hardness and chemical reactions to remove water hardness.

6. The teacher initiates a discussion, asking the pupils why they need more soap to achieve the desired effect of washing and washing in hard water. It encourages students to exchange insights.

7. The lecturer asks students to perform all interactive tasks - individual work.

Summary

1. The student indicated by the teacher sums up the lesson, telling what he has learned and what skills he/she has been practicing.

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

Soap in the fight for cleanliness - dirt removal mechanism

Adding soap to the water during washing reduces its surface tension. In the presence of soap, water moistens the hydrophobic surfaces better, thus the removal of dirt is easier. Soap supports the removal of dirt, interacting with its particles, which along with soapy foam float on the surface of the water.

It happens that during washing a floccose precipitate forms in the water. It happens when the water used for washing is hard.

Hard water contains significant amounts of calcium and magnesium salts dissolved in it. When cleaning and washing in hard water using soap, insoluble calcium and magnesium salts form as a precipitate. The soap used for washing does not foam, and the formation of foam is a necessary condition for removing dirt. Sample equations of reactions can be written as follows:

There are two types of water hardness - carbonate hardness (temporary) caused by the presence of calcium and magnesium bicarbonates, and permanent hardness, which is caused by other calcium and magnesium salts (chlorides, nitrates, sulphates) dissolved in water.

When water containing calcium and magnesium bicarbonates is boiled, reactions take place, as a result of which calcium carbonate and magnesium carbonate settle on the walls of the vessel (e.g. kettle) in the form of a solid, colloquially called fur. The process of removing temporary hardness, resulting from the presence of calcium ions in water, is described by the equation:

${\mathrm{Ca}}^{2+}+2{\mathrm{HCO}}_3^{-}\to {\mathrm{CaCO}}_{3\downarrow }+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2$

${\mathrm{Mg}}^{2+}+2{\mathrm{HCO}}_3^{-}\to {\mathrm{MgCO}}_{3\downarrow }+{\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2$

Calcium and magnesium ions that cause water hardness are removed. The water softening effect is obtained. Therefore, carbonate hardness is called temporary hardness. Water hardness is most often expressed in German or French degrees.

German degree [°n] is equal to the amount of salts contained in water, which is chemically equivalent to 10 mg CaO.

French degree [°f] is equal to the amount of salts contained in water, which is chemically equivalent to 10 mg CaCOIndeks dolny 3₃.

Manufacturers of washing machines and dishwashers often warn against the action of hard water on these devices and recommend – to protect them from scaling – using water softeners. Information whether the water we have in the tap is hard is also important for aquarium fish farmers and users of water filters. Currently, products for testing the hardness of water at home are available.

• Soaps effectively remove dirt because they are surface‑active substances. Their specific structure - the presence of a hydrophilic head and a hydrophobic tail - reduces the surface tension of water.