Topic: Soap in the fight for cleanliness — obtaining and properties of soaps

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:

8) describes the saponification of fats; writes relevant equations of reaction;
9) explains how fatty acids or soaps are obtained from glycerides; writes relevant equations of reaction.

High school and technical high school – extended level:

XVII. Esters and fats. Pupil:

9) describes the process of saponifying fats; writes appropriate reaction equations;
10) explains how fatty acids or soaps are obtained from glycerides; writes appropriate reaction equations.

Old core curriculum:

High school and technical high school – basic level:

XVII. Esters and fats. Pupil:

8) describes the saponification of fats; writes relevant equations of reaction;
9) explains how fatty acids or soaps are obtained from glycerides; writes relevant equations of reaction.

General aim of education

The student acquires knowledge and skills about the topics discussed in the classes

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to describe the properties of soaps;

• to classify soaps due to physical state, hardness, solubility in water and exchange examples of soaps;

• to explain what the saponification of fats consists in;

• to discuss using the scheme (drawing) the mechanism of action of soap on dirt and mark hydrophobic and hydrophilic fragments in formulas and models of surfactants;

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

• to justify how hardness of water affects the washing process, and suggest ways to investigate the impact of water hardness on the formation of sparingly soluble compounds when washing.

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 uses the reverse lesson method. The students were given the task of preparing for classes, using the e‑textbook and the Internet, information about soaps: historical outline, classification due to the state of aggregation, hardness and solubility in water and properties. Selected students, as assistants, present the developed content.

2. The teacher divides the students into groups and refers them to the abstract, informing them that they will follow the instructions in Experiment 1 - „Getting soap from stearic acid and sodium hydroxide”. He asks them to formulate a research question and hypothesis, and then write them down in the form in an abstract. Students conduct experiments, observe changes, and then discuss to receive applications. Then they write on the board the equation of the soap receiving reaction, discussing its mechanism - the teacher oversees this stage, explains the uncertainty, possibly translates the soap process again and summarizes the information. Students write notes and conclusions on the form in the abstract, they also write the equations of reactions in notebooks.

3. The lecturer acquaints students with the issues of surfactants and surface tension of water. Presents the material using the photo gallery in the abstract. Then the teacher displays the film „Study of the maintenance of the needle on the surface of water and water with washing‑up liquid” from the abstract. After the screening of the film, the teacher invites the students to the discussion, asking the question: „Why do the skirs stay on the surface of the water and why the needle drowned?”.

4. In order to consolidate the record of the saponification reaction equation, he asks students to solve interactive exercises.

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.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Soap in the fight for cleanliness — obtaining and properties of soaps

Soaps are substances capable of foaming in water and removing dirt. Hard soaps used in households are sodium soaps with added fragrances and dyes. While potassium soaps are normally used as ingredients in other products, such as shaving creams and liquid cleaning products.
Soaps are metal salts of groups 1 and 2 (mainly sodium, potassium and magnesium salts), as well as salts of higher carboxylic (fatty) acids – most commonly of palmitic, stearic and oleic acid, for example:

• sodium palmitate ${\mathrm{C}}_{15}{\mathrm{H}}_{31}\mathrm{COONa}$,

• potassium stearate ${\mathrm{C}}_{17}{\mathrm{H}}_{35}\mathrm{COOK}$,

• sodium oleate ${\mathrm{C}}_{17}{\mathrm{H}}_{33}\mathrm{COONa}$.

Soap is a surface active substance. It works by lowering the surface tension of water. Look at the pictures and tell what is the surface tension.

The reaction of stearic acid with sodium hydroxide produces salt – sodium stearate (soap). The reaction proceeds according to the following equation:

The process of obtaining soap from fat, called fat saponification, can be presented as a following scheme:

$\text{fat + sodium hydroxide }\stackrel{\text{T}}{\to }\text{ sodium soap + glycerol}$
The reaction of producing soap from fat proceeds according to the following equation:

Fat saponification is used on an industrial scale to produce soap, mainly from saturated fats. This process involves the long‑term cooking of fats with concentrated sodium hydroxide solution. Glycerin produced alongside soaps is removed from the final product or sometimes left behind as it has a greasing effect. Currently, fatty acids obtained during the processing of crude oil are also used in soap production. Often, natural oils and fats, or a mixture of them, are used instead of pure fatty acids in soap production, which in the saponification process produce directly salts of the corresponding fatty acids.
Toilet soaps manufactured today are enriched with various additives – moisturizers, acidifying substances, antibacterial agents, fragrances, colouring agents, in order to enhance their skin care properties and make them more attractive to users.

• Soaps are obtained by neutralization of higher fatty acids with metal hydroxides of groups 1 and 2 (mainly sodium, potassium and magnesium hydroxides) and – on an industrial scale – by saponification of fats.

• Soaps are surface‑active substances. Their specific structure – the presence of hydrophilic head and hydrophobic tail – reduces the surface tension of water.

soaps, surface tension, surface‑active substance, hard water, fat saponification