Topic: Alkanes – chemical properties

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

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

4) observes and describes the chemical properties (combustion) of alkanes; writes the equations for combustion of alkanes with high and low oxygen availability; finds information about and uses of alkanes.

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:

• explain the effect of carbon chain length on the physical properties of alkanes, e.g. on the physical state;

• plan experiments to study the properties of alkanes on the example of methane and ethane;

• observe and describe physical and chemical properties (combustion reactions) of alkanes on the example of methane and ethane.

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, referring to the known students' physical properties of alkanes on the example of methane, asks for these properties to be mentioned.

2. The teacher informs the participants that he will conduct an experiment from the abstract „Testing of combustibility of gaseous hydrocarbons”. Students formulate a research question and hypotheses, write them in the observation diary in an abstract, and then observe changes during the experiment. After the experiment, they determine the conclusions regarding the chemical properties of methane (flammability check) and write them down.

3. The teacher writes on the board and discusses the equations of combustion of methane: total and incomplete (where products are carbon monoxide and water as well as carbon and water). He discusses the negative impact of afterdamp on the human body. He starts a conversation directed among those on safety in the event of gas system leaks at home and in the case of smoke poisoning.

4. The lecturer invites those interested to the table to „train” the ability to write equations of combustion reactions of alkanes, e.g. propane, butane, pentane.

5. The teacher informs that he will display a video from the abstract resource „Testing the reactivity of propane and butane against the aqueous solution of potassium permanganate”. Before the issue takes place, the lecturer explains the concept of „reactivity”. Students, as before, formulate a research question and hypotheses, write them down. They also note observations of the experiment and conclusions on the chemical properties (reactivity of alkanes) of alkanes.

6. 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

2. 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

Alkanes – chemical properties

One of the products of incomplete combustion of methane is carbon monoxide. It is a colourless, odourless gas which attaches to haemoglobin about 300 times faster than oxygen in a human body.
This bond is more durable than oxygen and haemoglobin. Tissues are deprived of adequate oxygen supply, which in many cases leads to death. Immediate blood transfusion is the only thing that may help.

That is why detectors which constantly monitor air for presence of carbon monoxide are installed in rooms at risk of carbon monoxide emission. When certain values of carbon monoxide concentration are exceeded, an appropriate warning is started.

Carbon dioxide and water are the products of complete combustion of other alkanes – as in the case of methane. On the other hand, carbon monoxide and water or carbon and water are products of incomplete combustion.
Thus the following products of complete combustion of ethane may be distinguished:

Incomplete combustion takes place with limited air access:

A mixture of methane and air at a volume concentration of 4.5–15% exhibits explosive properties.

Formation of this mixture when methane passes into closed rooms is often a cause of dangerous explosions, both in residential buildings and mines. In a mixture containing more than 15% of methane, this gas burns with a flame. An explosive mixture will explode, for example, under the influence of fire or an electric spark. That is why if you suspect gas leakage, close its supply and open your windows. Do not fire anything and do not turn electrical appliances on.

Leave your home immediately and notify gas rescue services (phone: 992).

• Physical properties of alkanes change if the length of carbon chain is increasing.

• Alkanes are compounds that are slightly reactive; they undergo combustion reactions at room temperature.

• Propane and butane do not react with potassium permanganate.