Topic: Mixing of substance - structure of matter and diffusion

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

I. Substances and their properties. Pupil:

4) explains the phenomena of diffusion, dissolution, and change of state of matter.

General aim of education

The student explain the phenomenon of diffusion.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to exchange substance concentrations with examples;

• to explain what the phenomenon of diffusion and contraction consists in;

• to plan experiences confirming the granularity of the matter structure.

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, in order to remind you of the nature message, emphasizes that everything that surrounds us - living organisms, bodies, solids, liquids and gases - is matter. We feel its presence directly with the help of the senses or indirectly, using various instruments that allow us to transform the imperceptible world for sensory impressions. The substances that make up the matter that surrounds us are made of small, invisible grains - molecules or atoms. These particles interact with each other: they attract or repel. Therefore, we say that the matter has a granular or molecular structure. The substances viewed with the naked eye look like a uniform material - only when you look at them enlarged, eg under an electron microscope, you can see that they are made of a large amount of particles.

2. The teacher asks students to define the concept of substance.

3. The teacher asks the students how they know the substance's concentrations and asks for examples. Then he instructs them to consider the distribution of particles in individual states of concentration - initiates a discussion, in the summary of which he presents an illustration of „States of matter concentration”.

4. The teacher asks students what experiment they will propose to confirm the granular structure of matter - there is a short discussion. Students receive job cards - the lecturer asks to formulate a research question and hypotheses and note them in the job cards. Then, the students watch the film „The process of mixing water and ethanol” - after the screening, the teacher asks what they have noticed, and instructs them to write observations and an agreed motion in the observation cards.

5. When discussing diffusion in gases, the teacher gives an example of a fragrance in a bakery, in a shop selling cured meats, incense in an apartment, sprayed deodorant in the bathroom, cooking dinner in the kitchen and the like. Then, in the form of a show, he presents the students with experiments according to the instructions described in the abstract - „Examination of the spread of the fragrance of perfumes” and „Examination of the spread of the fragrance of the oil”. In reference to the examples cited, he introduces the concept of diffusion and gives its definition.

6. At the end of the lesson, the teacher asks students to do interactive exercises.

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

Mixing of substance - structure of matter and diffusion

Everything around us is matter. It is made of particles (it has a granular structure). In the solid substance, the particles are arranged close to each other in a regular manner. In liquids the distances between the particles are usually larger and the particles are arranged irregularly. However, in gases the distances between irregularly arranged particles are the largest (which means at the same time that the interactions between particles are the smallest in this case).

The phenomenon of volume reduction when mixing liquids is called contraction. The reason for contraction is the possibility of stiffer packing of particles in a mixture of two liquids. The mechanism of contraction can be presented in a model way, using for example peas and poppy seeds.

Fragrances of cosmetics, flowers or cooked and fried foods are spreading throughout the apartment. The air freshener slowly releases the pleasant fragrance that we feel in the room. The scent of hairspray after a short moment becomes noticeable away from the place of its spraying. The examples cited illustrate the process of spreading the substance fragrance by itself from the place where it is focused, to places where there is less or none smell, which leads to equalization of concentrations. This is the phenomenon of diffusion.

Advection

The transmission of smell in the air does not always occur by itself, it can be caused by the phenomenon of advection (horizontal movement of molecules of the transported substance). It causes the inflow of air with different properties (e.g. with different temperature or humidity). The phenomenon of advection in combination with diffusion is called convection (vertical movement associated with heat movements, with movements caused by temperature difference).

There are following types of advection:

• forced, e.g. draught in the room;

• natural, caused by differences in the density of the medium due to temperature or concentration differences.

Diffusion of gases is quite slow process, for example, the shift of ethanol vapours in the air at a distance of 1m takes about 100,000s, which lasts for over 1 day! Thanks to the advection effect with almost imperceptible air flow (10 cm/s), the fragrance is transferred to a distance of 1 m in just 10 seconds!

A special type of diffusion is osmosis, which occurs in aqueous solutions, penetrating the semi‑permeable membrane separating two solutions of different concentration. Osmosis proceeds spontaneously, from a solution with a lower concentration of dissolved substance to a solution with a higher concentration, i.e. it leads to equalization of the concentrations of both solutions.

• Matter is made of particles that are constantly in motion. Matter has a granular structure.

• The most important phenomena confirming the discontinuity of matter are: diffusion, dissolution of solids in liquids, mixing of liquids, changes in the state of matter.

• Diffusion in gases and liquids occurs faster than in solids.