Topic: Emulsion as a colloidal system

Target group

High school / technical school student

Core curriculum:

New core curriculum:

High school and technical high school. Chemistry – basic level:

XXI. Chemistry around us. Pupil:

3) describes the formation of emulsions, their uses; analyzes the composition of cosmetics (e.g. based on labels for cream, lotion, toothpaste, etc.) and searches in available sources for information on topic of their operation.

High school and technical high school. Chemistry – extended level:

XXI. Chemistry around us. Pupil:

3) describes the formation of emulsions, their uses; analyzes the composition of cosmetics (e.g. based on labels for cream, lotion, toothpaste, etc.) and searches in available sources for information on topic of their operation.

Old core curriculum:

High school and technical high school. Chemistry – basic level:

XXI. Chemistry around us. Pupil:
11) describes the formation of emulsions, their applications; analyzes the composition of cosmetics (based on the label of a cream, balsam, toothpaste, etc.) and searches in available sources for information on their operation.

General aim of education

The student explains the concept and discusses the use of emulsions.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn;

• mathematical competence and basic competences in science and technology.

Criteria for success
The student will learn:

• to explain the concept of emulsion;

• to discuss the use of emulsions with an indication of various examples of such compounds;

• to discuss the basic composition of the emulsion;

• to explain what an emulsifier is and how it works;

• to give the composition of selected emulsions, e.g. cream, balm, toothpaste;

• to discuss the methods of operation of various cosmetics, e.g. cream, lotion, toothpaste;

• to justify differences in the activity of moisturizing and oiling emulsions on human skin.

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;

• 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 teacher instructs the mentees to read the initial fragment of the abstract. Students ask each other about his acquaintance.

2. The teacher asks students what emulsions are and asks them to write down a formulated research question and hypothesis in the form provided in the abstract. Then it displays a movie titled „Emulsions” And students note their observations and conclusions. The teacher indicates the person who shares his insights and explains the reasonableness of the conclusions he has made.

3. The teacher presents and discusses photos and illustrations in an abstract. Students analyze them and answer the teacher's questions.

4. The teacher announces a movie entitled „Determination of the type of cosmetic emulsion”. Instructs students to write a research question and hypothesis in the form provided in the abstract. Then it displays the video and the students record their observations and conclusions. The teacher encourages young people to discuss, referring to the conclusions presented earlier.

5. Students read the fragment „Cosmetic Emulsions”. Then, working in pairs, they analyze the data in the table.

6. The teacher plays the recording of the abstract. Every now and then he stops it, asking the students to tell in their own words what they have just heard.This way, students practice listening comprehension.

7. Students perform an interactive exercise. The teacher makes sure that the task has been correctly completed and gives feedback.

Summary

1. Teacher asks: If there was going to be a test on the material we have covered today, what questions do you think would you have to answer? If the students do not manage to name all the most important questions, the teacher may complement their suggestions.

Homework

1. Imagine that you have the opportunity to interview an academic - a specialist in the field of today's lesson. What questions would you like to ask him? Write them down.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Emulsion as a colloidal system

Two liquids, such as water and alcohol, when mixed form a true (molecular) solution, in which there is no boundary between both liquids. Other liquids, such as oil and water, do not mix with each other, but they form two separate layers. This is why oil molecules cannot overcome the forces that bind polar water molecules.

When you mix water and oil, oil drops are dispersed in the water – this is how emulsion is created. The difference in surface tension between mixed substances plays an important role in this process – the less it is, the easier is to create emulsion. Dispersion by shaking, intense mixing requires work. Such emulsion is unstable – after some time these liquids will again divide themselves into two layers – oil (with lower density) stays on the top and water remain on the top. Emulsion will be fixed is you add dishwashing soap, which is the so‑called emulsifier.

Emulsions are systems consisting of immiscible liquids, where one liquid is dispersed in the second one as tiny drops. One phase (layer) is usually created by water, while the second one is an liquid immiscible with water, called the oil phase. As the structure is fragmented, emulsion seems to be homogeneous, while its heterogeneous structure can be observed only under a microscope (due to the size of dispersed phase). Emulsions are a certain type of colloids.

In colloidal solutions, the solute particle sizes are larger than in true solutions and range from 10Indeks górny -7^-7to 10Indeks górny -9^-9 m. These solutions consist of the dispersing phase which plays the role of a solvent and dispersed substance (phase) which corresponds to a solute in true solution. They scatter light falling on the solution. This is the typical property of colloidal solutions and is called the Tyndall effect.

The structure of an emulsion can be described using their phase system and volumetric ratios. Due to the mutual phase system, two types of water‑in‑oil w/o and oil‑in‑water o/w emulsions can be distinguished.

There are also multiphase emulsions – in their case it is not possible to determine exactly which phase is dispersed and which is being dispersed, because each one contains drops from the other phase.

Emulsion may be stable due to the presence of emulsifiers. An emulsifier usually dissolves better in one of two phases.

Emulsifiers are surfactants with hydrophobic and hydrophilic properties that form a molecular layer on the surface of the droplets of the dispersed liquid. The examples of emulsifiers include for example soaps, detergents, esters of polyhydric alcohols and natural substances such as gelatin, agar‑agar, lanolin, lecithin, and gum Arabic.

The simplest cream consists of fat, water and an emulsifier. Often creams contain more than one emulsifier because it ensures better stability and ensures that it will not break into layers. Some emulsifiers are both hydrophobic and hydrophilic. They are good for health and healthy look, for example lecithin, lanolin, cholesterol.

Each cosmetic emulsion consists of a fat‑wax base, emulsifiers, additional raw materials and water. Its ingredients are selected based on the purpose and mode of action of the cosmetic preparation as well as on the emulsion type we intend to obtain. Creams, lotions and cleansing milks are typical examples of emulsions.
The consistency or density of emulsions depends on the content of the dispersed phase, emulsifier type, viscosity of dispersed phase and presence of substances in this phase that affect the consistency of the cosmetic.

• An emulsion is composed of microscopic droplets of liquids dispersed in the entire volume of the second liquid. Mayonnaise is an emulsion in which small droplets of vinegar are dispersed in vegetable oil. Milk is an emulsion in which fat droplets are dispersed in an aqueous solution. Typical emulsions are mixtures of water‑insoluble (organic and mineral) oils and water.

• Types of emulsions one of the components of which is water: O/W (oil in water) – oil is the dispersed phase, water is the dispersing phase, for example milk; W/O (water in oil) – water is the dispersed phase, oil is the dispersing phase, for example margarine.

• It is not possible to obtain a stable emulsion without an emulsifier which binds hydrophobic and hydrophilic liquids. These are surfactants the structure of which make them arrange themselves along the boundary of both liquids. A part of them is immersed in a hydrophilic polar liquid and the other in a hydrophobic liquid. An emulsifier is needed to create an emulsion and increases its stability.

• Emulsifiers are widely used in pharmacy and food industry, for example lecithin is used to produce margarine.