Topic: Alcohols - properties

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

IX. Hydrocarbon derivatives. Student:

2) examines selected physical and chemical properties of ethanol; describes the properties and applications of methanol and ethanol; writes down the combustion equations of methanol and ethanol; describes the negative effects of methanol and ethanol on the human body.

General aim of education

The student investigates and describes selected physical and chemical properties of methanol and ethanol

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to list and discuss the properties of methanol and ethanol;

• to distinguish methanol from ethanol based on physical properties;

• to save the combustion equations of methanol and ethanol;

• to save and explain what alcoholic fermentation consists of.

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 the students to the issue of the properties of alcohol - he emphasizes that with the help of the senses of sight, taste and smell, it is not possible to distinguish methanol from ethanol. This fact is - in the case of alcohol consumption - the cause of severe poisoning and even death. It displays on the multimedia board the equation of the alcoholic fermentation reaction in verbal and summary formulas.

2. The teacher runs the show - determining the state of focus, the color and the smell of methanol and ethanol (willing pupils can check the smell). Students define the characteristics of alcohol and discuss the distinction between methanol and ethanol after these properties.

3. The teacher displays the film „Mixing ethanol with water” on the multimedia board. The students formulate a research question and hypotheses, write them in the form in an abstract form, and after the projection also note observations and conclusions. The lecturer explains the phenomenon of volume contraction..

4. The teacher refers students to the table „Physical properties of methanol and ethanol” in the abstract - they are to carry out its analysis with particular reference to boiling point and alcohol density.

5. The lecturer displays on a multimedia board and together with the students discusses the illustration from the abstract „Pictograms determining the type of threat”.

6. The teacher displays on the multimedia board a film from the abstract „Testing the reaction of an aqueous solution of ethyl alcohol”. The students, as before the screening, formulate a research question and hypotheses. The teacher asks students to compare the structure of alcohols and hydroxides, determine whether differences in the structure of these substances affect the pH of the solution. Students provide answers and then observe changes during the experiment being displayed. They draw conclusions, write them in an abstract.

7. The lecturer presents the „ethanol flammability test” - students determine the color of the flame.

8. The teacher records and discusses the equations of incomplete methanol burning, paying attention to reaction products. Then he asks those willing to the table to write the equations of the total and incomplete combustion of the indicated alcohols.

9. 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

Alcohols - properties

Methanol and ethanol are colourless liquids that dissolve well in water. Therefore, these cannot be distinguished without laboratory tests, e.g. determination of boiling point or density. In trade, concentrated ethyl alcohol is called grain alcohol.

As we know, the process of alcohol fermentation occurs under the influence of a special species of yeast found in the peels of ripe grapes (or other fruits). Glucose – sugar contained in fruit juice – under favourable conditions, undergoes a chemical reaction where product is ethyl alcohol.

Reaction equation – in words:

$\text{glucose}\stackrel{\text{yeasts}}{\to }\text{ethyl alcohol + carbon dioxide}$

Reaction equation – molecular form:

${\text{C}}_{\text{6}}{\text{H}}_{\text{12}}{\text{O}}_{\text{6}}\stackrel{\text{yeasts}}{\to }{\text{2CH}}_{\text{3}}{\text{CH}}_{\text{2}}\text{OH +}{\text{2CO}}_{\text{2}}$

The reaction equation shows that alcohol fermentation is a process that takes place under the influence of yeast. Its products are ethyl alcohol and carbon dioxide.

The contraction phenomenon is taken into account in the spirits industry in the technological processes and in the calculation of production efficiency. When adding 50 litres of water to 50 litres of ethyl alcohol (grain alcohol), not 100 but 96.3 litres of solution are produced.

A mixture of ethanol and water with a 95.6% ethanol content is called grain alcohol.

By examining methanol and ethanol, we will answer the following questions:

• What are chemical properties of alcohols?

• Is there any similarity in their behaviour during chemical reactions?

• Does the presence of the $\text{–OH}$ functional group in alcohol molecules affect the pH of their aqueous solutions?

Both methanol and ethanol are characterized by a sharp, irritating odour. Testing these alcohols only with smell can lead to confusion.

Do aqueous solutions of alcohols undergo electrolytic dissociation? Is the pH of aqueous solutions of alcohols the same as the pH of bases, since they have a hydroxyl group similar to hydroxides? For testing the pH of aqueous solutions of alcohols, known indicators can be used: red cabbage brew, phenolphthalein solution, universal indication strip

Ethanol is a flammable substance. With unrestricted oxygen access, a complete ethanol combustion occurs.

When the fire torch is moved closer, the alcohol vapour ignites. The alcohol burns with a bluish flame. The products of the total combustion of ethanol are carbon dioxide and water: ${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH + 3}{\text{O}}_{\text{2}}\text{→ 2C}{\text{O}}_{\text{2}}\text{+ 3}{\text{H}}_{\text{2}}\text{O}$

The products of the total combustion of methanol are carbon dioxide and water:

$\text{2C}{\text{H}}_{\text{3}}\text{OH + 3}{\text{O}}_{\text{2}}\text{→ 2C}{\text{O}}_{\text{2}}\text{+}\text{4}{\text{H}}_{\text{2}}\text{O}$

Incomplete combustion takes place under conditions of limited oxygen supply.

${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH}\text{+}\text{2}{\text{O}}_{\text{2}}\text{→}\text{2CO}\text{+}\text{3}{\text{H}}_{\text{2}}\text{O}$

$\text{C}{\text{H}}_{\text{3}}\text{OH +}{\text{O}}_{\text{2}}\text{→ CO + 2}{\text{H}}_{\text{2}}\text{O}$

${\text{C}}_{\text{2}}{\text{H}}_{\text{5}}\text{OH +}{\text{O}}_{\text{2}}\text{→ 2C + 3}{\text{H}}_{\text{2}}\text{O}$

$\text{2C}{\text{H}}_{\text{3}}\text{OH +}{\text{O}}_{\text{2}}\text{→ 2C + 4}{\text{H}}_{\text{2}}\text{O}$

• Methanol and ethanol have many common physical properties and are therefore difficult to distinguish.

• Methanol is a poison.

• Only methanol, ethanol and propanol are well soluble in water, each subsequent alcohol in the homologous series already less.

• The pH of aqueous solutions of alcohols is neutral.

• Methanol and ethanol are flammable substances. These are subject to complete and incomplete combustion reactions.

alcohol, hydrocarbons, monohydric alcohols, methanol, ethanol, methyl alcohol, ethyl alcohol, volume contraction