Topic: Polyhydric alcohols

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

IX. Hydrocarbon derivatives. Pupil:

3) writes the sum and semi‑structural (group) formula of propane‑1,2,3‑triol (glycerol); investigates its physical properties; mentions its uses.

General aim of education

The student describes the structure, selected properties and use of glycerol and ethanediol

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• explain the term: polyhydric alcohol;

• record the total and structural formula of glycerol and ethanediol;

• list and discuss the properties of glycerol and ethanediol;

• record the combustion reactions of glycerol and ethanediol;

• design and carry out experiments to study the properties of glycerol;

• mention the use of glycerol and ethanediol.

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.

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 introduces students to the issue of polyhydric alcohols, giving a few examples from our surroundings, where they apply, and of which we often do not realize. Then he discusses the construction and naming of polyhydric alcohols. First, he writes down the total glycerol formula on the board. He divides students into groups, distributes ball‑and‑ball models and asks for building a model of a glycerol molecule - checks the correctness of arranged formulas. Writes on the table the structural formula of propane, and next to glycerol, discusses the principles of naming, gives common and systematic names (glycerol, glycerol, propanetriol, propane‑1,2,3‑triol) and writes the semi‑structural formula.

2. The lecturer discusses the construction and rules for naming etanediol. Writes the summary formula of this alcohol on the board and asks students to build a model of the molecule - checks the correctness of the task. He writes on the board the structural formula of ethane, and next to the structural formula of ethanediol and explains the principles of naming (he gives both the names etanediol and ethylene glycol). Records the semi‑structural formula of this alcohol. Students write formulas and names in notebooks. To illustrate the structure of polyhydric alcohols, the teacher refers to yet another example of this group of alcohols - erythritol (erythritol) and acts similarly to glycerol and ethanediol. On the summary displays the presentation from the abstract „Construction of the model of erythritol molecule”.

3. The teacher runs a demonstration - determining the state of aggregation, color and smell of glycerol. The students indicate the characteristics of this alcohol, they write observations in the work sheets.

4. The teacher asks students to analyze the „Physical properties of glycerol” in the abstract, with particular reference to the boiling point, and to compare this parameter with the methanol and ethanol characteristics.

5. The lecturer displays on the multimedia board a film from the abstract „Glycerol Flammability Test”. Students - as before - formulate a research question and hypotheses, write them in an abstract; similarly they follow the observations and conclusions from the experiment. The teacher writes on the board and discusses the notion of incomplete combustion of glycerol (products: coal and water).

6. The teacher displays on the multimedia board a film from the abstract „Testing the reaction of an aqueous solution of glycerol”. Students formulate a research question and hypotheses, write them in an abstract, and after the projection also note observations and conclusions.

7. The lecturer presents the „Testing the electrical conductivity of an aqueous glycerol solution” - note in the methodical commentary. The students act as in the previous point of the scenario.

8. The teacher asks students to do interactive exercises in the abstract.

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

Polyhydric alcohols

Glycerol, commonly called glycerine, is a propane derivative in which three hydrogen atoms have been replaced with hydroxyl groups. Hence the name propanetriol. The first component (propane-) originates from a hydrocarbon whose chain is part of the alcohol, tri- means three groups $\text{–OH}$, and -ol ending is characteristic of alcohols.

Propane‑1, 2, 3‑triol is the systematic name of glycerine. As explained above, propane - indicates that this compound is a propane derivative, numbers: 1, 2, 3, so‑called. locants, inform that each hydroxyl group (hydroxyl group) is connected to another carbon atom, numeral tri- defines the presence of three hydroxyl groups, and -ol ending confirms that glycerol is part of alcohols.

${\text{C}}_{\text{3}}{\text{H}}_{\text{5}}\text{(O}{\text{H)}}_{\text{3}}$

Ethylene glycol is a derivative of ethane, in which two hydrogen atoms have been replaced with hydroxyl groups. The systematic name of this compound is ethanediol.

Glycerol (glycerine) is a colourless liquid, freely soluble in water. The boiling point and the density of the liquid are the substance‑specific quantities and allow the identification of the alcohol in question.

By conducting further experiments, we will see what the chemical properties of glycerol are. Does it react like ethanol? Does the presence of three hydroxyl groups affect the reaction of aqueous glycerol solutions? Are warning signs placed on the glycerol labels?

Glycerol has no smell. It has a sweet taste and this feature is of great importance for its various applications.

Glycerol, like other alcohols, undergoes combustion. It is necessary to preheat glycerol in order to start the reaction. Depending on the amount of available oxygen, the glycerol combustion may be complete or incomplete.

In cosmetics there are two types of glycerol – natural and of petrochemical origin. Glycerol is obtained, among others from coconut oil.

Glycerol has hygroscopicproperties and naturally protects the skin by binding the water necessary to maintain proper skin hydration. Effectively moisturizes dry skin. It smoothens skin, improves elasticity, regulates skin renewal processes. It is added to almost all hand creams, face creams and balms.

Glycerol is used as a sweetener in antitussive syrups. It is also used in the production of explosives (nitro glycerine). It has many applications in medicine because it is easily absorbed into the gastrointestinal tract. Oral glycerol preparations have a mild laxative effect.

Crude glycerine obtained from vegetable fats is used as an additive to cattle feed (for cows and pigs). It is tasty, maintains feed moisture, provides energy and affects e.g. cow's milk yield and pig mass gain.

Ethylene glycol is a colourless liquid with a high viscosity. It dissolves well in water. It is a poisonous substance. It is used in the manufacture of artificial fibres, paints and anti‑freezing engine coolants.

Ethanediol is toxic for humans. After consumption, it causes metabolic acidosis and damages to many organs, kidneys, liver and brain.

• Glycerol and glycerine are common names of the same chemical compound – propanetriol.

• The glycerol molecule consists of three hydroxyl groups.

• Glycerol is a thick oily, colourless and odourless liquid with a sweet taste. It is not a poisonous substance.

• Glycerol is widely used in the cosmetics, food and textile industries.