Topic: Alkynes - properties of unsaturated hydrocarbons

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Elementary school. Chemistry.

VIII. Compounds of carbon with hydrogen - hydrocarbons. Student:

6) on the basis of the observations describes the physical and chemical properties (combustion, bromine incorporation) of ethene and ethyn; searches for and uses information about their uses;

8) designs and conducts experience allowing to distinguish hydrocarbons saturated from unsaturated

General aim of education

The student discusses the properties of alkynes.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• what properties have eten and etin;

• to design experience to distinguish saturated hydrocarbons from unsaturated hydrocarbons.

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 asks students to execute the 3 command from the abstract and to familiarize themselves with the physical properties of the alkynes (with particular reference to the table „Physical properties of alkynes”). Initiates a discussion about these relationships - it should end with the conclusions that students write in the notebooks..

2. The teacher performs with students the experiment „Combustion of alkynes”. The teacher instructs students to formulate a research question and hypothesis and to write them down in work sheets - observations and conclusions from the experiment should also be written down. After the experiment, he or she asks those willing to write on the board the equations of the total combustion reaction and both incomplete combustion reactions..

3. The teacher displays a film from the abstract „Ethin reactivity with bromine”. Similarly to the previous film, the students write a research question, hypotheses, observations and conclusions about the experiment viewed in the work sheets. They then receive the command: „Explain what the differences between ethane, ethene and ethane molecules”..

4. The teacher displays, using the abstract, the equation of the addition (ethion) reaction with bromine and discusses its mechanism. Explains the rules for the creation of new names, as reaction products of attachment, of chemical compounds. Then it displays the equation for hydrogenation of etin and also discusses its mechanism. Invites people to the table, to write the equations of attachment reactions on structural formulas and to create the names of reaction products, e.g., ethine with chlorine, ethane with hydrogen bromide, ethanol with hydrogen chloride..

5. The teacher asks students (individual work) to perform tasks and interactive exercises in an abstract..

Summary

1. The teacher asks the students to finish the following sentences:

   • Today I learned ...

   • I understood that …

   • It surprised me …

   • I found out ...

   The teacher can use the interactive whiteboard in the abstract or instruct students to work with it

Homework

1. 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

Alkynes - properties of unsaturated hydrocarbons

The physical properties of alkynes change with the increase in the number of carbon atoms in their molecules – these transform from the gas state, through the liquid state, to the solid state. Alkynes have similar properties to alkanes and alkenes.

Analyze the reaction scheme of ethyne with bromine in an anhydrous environment proceeds according to the equation. Then watch a movie showing the course of the reaction.

${{\text{C}}_{\text{2}}\text{H}}_{\text{2}}\text{+}{\text{2Br}}_{\text{2}}\text{→}{{\text{C}}_{\text{2}}\text{H}}_{\text{2}}{\text{Br}}_{\text{4}}$

As a result of this reaction, a multiple (triple) bond breaks and a saturated tetrabromoethane compound is formed (the prefix tetra- indicates that there are four bromine atoms in the molecule). This type of reaction is called the addition reaction. Acetylene and other alkynes easily undergo addition reaction including with hydrogen, halogens (e.g., chlorine). As a result of these reactions, saturated compounds with single bonds between carbon atoms may be formed. Hydrogenation of ethyne:

• The physical properties of alkenes and alkynes are similar to the physical properties of the alkanes. These change as the number of carbon atoms in the chain increases.

• Alkenes and alkynes are chemically reactive, combustible, and are subjects to addition reactions.

• Alkynes are more reactive than alkenes.