Lifelong Learning Programme

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Title of the Experience
How to achieve that students can understand difference between chemical pure matter and mixture
Name of the teacher
Katarína Javorová
Country where it took place
School typology
Lower Secondary School
Thematic Area
Experience typology
Teaching in class
Type of contact
Description of the Experience
The theme of chemically pure substances and compounds is discussed and thought in grade 6 or grade 7 of an elementary school. Students could have met with the concept of substance already in the 1st level of elementary school in the subject of Natural Science. From my experience, students can not distinguish whether it is a chemically pure substance or a compound mixture. The problem I see is that the chemical elements and compounds are parts only in 8th grade primary school curriculum and often pupils do not know them all. Many times it happens that pupils can not name substances or compounds they encounter in their every day lives. For example, everything that is transparent is for them water.
Given topic is divided into three lessons. One class is of the basic type and two classes consist of laboratory exercises.
In the initial first class, students receive a worksheet with tasks. They solve different tasks throughout the lesson. The first task is a crossword with the topic of concepts related to the subject of chemically pure substances and compounds (substance, mixture, suspension, emulsion, foam, aerosol, smoke, solution, solvent, water ...). When pupils find out all the concepts, we discuss together which of them they know and what they think it is represented underneath the terms. Their arguments and assumptions should be entered in their workbooks (on paper). Consequently, pupils receive a study text, which contains all the terms explained. Each student reads the text by him or herself. Jointly we define the necessary concepts and pupils make notes in their notebooks. Finally, the end of the class is devoted to an independent work, addressing other problems from the worksheet – filling in the schemes (division of substances, separating mixtures), determining whether the substance is chemically pure or a mixture, topping the right words in the text, while students help themselves with the study text they received. Eventually the final stage of the lesson is a control of accuracy that we make together as a whole class and a summary of the curriculum.
The following two lessons are designed as laboratory exercises and focus on practical experience with various mixtures. Each laboratory class begins with the necessary repeating of the concepts and typing down the problematic task. During the first laboratory class, the students learn how to prepare a solution (with the correct quantities of the substance, unsaturated, saturated, supersaturated), which substance may be a solvent, which substances are soluble in water (working with chemical tables). They solve problem tasks: Task #1: Is every substance soluble in water?, Task #2: Although the substance is soluble in water is it in an unlimited way?. They prepare the solutions of salt and sugar. They will learn to measure how to properly prepare a solution. Prepared solutions are saved for purposes of other following laboratory exercises containing of methods of separating components of a mixture (evaporation, crystallization, and filtration). At the end of the lesson they fill in a prearranged protocol of laboratory exercises and respond to problematic tasks, based on the findings during the implementation of training solutions. During the second class of laboratory exercises students prepare mixtures of different types - suspension, foam and emulsion, all from available substances. They solve problem tasks: Task #1: How the (chemically pure) substances change if they will get mixed together? Task #2: What ingredients do I have to mix so I got a suspension, an emulsion or foam? They work in small groups (two maximum three students). During laboratory exercises I suggest to the students to make photos or videos that can later serve them well in home preparation. As in previous laboratory exercise class they also make a laboratory protocol. At the end of the class we are discussing how it would be possible to get back individual substances (components) of a mixture. It is already a preparation for the next lesson - methods of separating components of a compound.
After these three lessons, pupils are more aware of the difference between pure substances and mixtures, as based on their own observations and practical design they were able to detect differences between them. Students enjoy this form of teaching while having fun. They like doing experiments and finding by themselves the connections to theory. They can better remember and imagine different types of mixtures and later apply them in other examples. They can easier apply them and use them during the following topic of method of separating components of a mixture, because they have their own experience of developing various types of mixtures.
This type of experience is to be deemed as successful-positive.

Comments on this Teachers Experience

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Date: 2014.11.26

Posted by Anita Krismane (Latvia)

The proposed example is a model of good practice for motivation to learning process.


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