Topic: Extraction and chromatography as a methods of separating and identifying mixtures

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

I. Substances and their properties. Student:

6) prepares mixtures and selects a method for separating the components of the mixtures (e.g. filtration, distillation, separation of liquids in the separator); indicates those differences in physical properties of the components of a mixture that enable the mixture to be separated.

General aim of education

The student discusses, plans and conducts extraction and chromatography while observing the principles of health and safety

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• what the methods are for separating homogeneous and heterogeneous mixtures;;

• what laboratory techniques are used to separate mixtures;;

• to plan chosen methods for separating mixtures into components and to perform appropriate actions yourself;;

• to describe the possibilities of using the methods for separating of mixtures at home and in industry;;

• to use basic terms pertaining to mixtures and the way to separate them..

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

• exposing

  • exposition.

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 prepares the students for conducting experiment 1 – “Extraction” by playing the video from the abstract on the interactive whiteboard. The teacher divides students into groups (or agrees on pairs), hands out instructions on the experiment and asks the students to read them. While the students read the materials, the teacher gives them worksheets in which they write down their observations and conclusions. The teacher then asks the students to formulate the research problem – if the research question is identified, the students write it down in the worksheet and start the experiment. They observe its course. After the activities, the teacher asks the students about observations and then asks them to write them down in the worksheet.

2. After the first research work is completed, the teacher asks the students to define the concept of extraction based on their own work. The teacher asks the question: What kind of mixture did you obtain in the conducted experiment? Then, the teacher instructs them to work with the e‑textbook and to gather information about the uses of extraction.

3. The teacher introduces the students to the problem of chromatography. The teacher plays (from the abstract) the film “Chromatographic separation of the photosynthetic pigments of garden rocket leaves” and then explains what this process consists in. Referring to the extract obtained in experiment 1, the teacher discusses experiment 2, in which this extract will be used.

4. The teacher determines which groups/pairs will conduct experiment 2 – “Chromatographic separation of photosynthetic pigments of lettuce leaves (optionally garden rocket or other plants)” and which groups/pairs will conduct experiment 3 – “Chromatographic separation of the pigments in marker pen ink” (description in the methodological note). The teacher hands the students appropriate instructions on how to carry out the research work and asks them to familiarize themselves with them. After a while, the teacher tells the students to formulate the research problem, write it down on the worksheet and start carrying out the experiments. Students closely observe the course of the experiment – the teacher asks them for their observations. Once the observations have been agreed together, the students write them down in the worksheet. They also formulate and record the conclusions of their observations.

5. At the end of the lesson, the teacher asks the students to do the interactive exercise from 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.

Methodological note:

Experiments 1 and 2

The list of necessary teaching materials aids.

Materials: leaves of green and red lettuce, small pieces of porcelain, cotton wool, wooden sticks (a toothpick and a skewer)

Laboratory equipment and glassware: alcohol/gas burner, test tubes, test tube stands, pipettes/droppers for reagents, test tube holder, reflux condenser, SSC cap for discharging of gases, graduated Pasteur pipettes with a cut‑off section of the tank (chromatographic column), capillary Pasteur pipette, plastic teaspoon

Reagents: ethanol (spirit), extract from lettuce leaves in the experiment, potato starch

1. Problem‑focused and discovery experiment

“Extraction of photosynthetic pigments of lettuce leaves (optionally garden rocket or other plants)”

Performing the experiment

Pour approx. 2 cmIndeks górny 3³ of ethanol into a tube placed in a test tube stand and throw a piece of porcelain in. Next, add a fragmented leaf of lettuce (or another plant), which should be completely immersed in the liquid. Close the tube with the SSC cap with the mounted reflux condenser. Heat up the contents of the tube, letting them boil for a few minutes, then leave the tube in the tube stand. Observe.

2. Problem‑focused and discovery experiment

“Chromatographic separation of photosynthetic pigments of lettuce leaves (optionally garden rocket or other plants)”

Performing the experiment

Put a small ball of cotton wool into the ‘chromatographic column’ (graduated Pasteur pipette with a cut‑off section of the tank) and press the ball down using a skewer. Next, pour in potato starch up to the last line of the graduation, then put the cotton ball in and press it down with a stick. From the top, pour a small amount of the extract from leaves obtained in the first experiment and add ethanol up to the mid‑point of the tank. Place it all in an empty test tube and observe what happens.

3. Problem‑focused and discovery experiment

“Chromatographic separation of the pigments in marker pen ink”

The list of necessary teaching materials aids.

Materials: marker pens / felt‑tip pens

Laboratory equipment and glassware: beaker/jar, filter paper

Reagents: vinegar or acetone

Performing the experiment

At a distance of about 1.5 cm from one end of the paper, draw dots using felt‑tip pens (one dot about 2 cm from the other). Pour vinegar into the beaker up to the height of 1 cm and put the paper in with the dots facing down. Put it on the bottom of the beaker. Observe what happens.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Extraction and chromatography as a methods of separating and identifying mixtures

Extraction consists in washing desired components out of a solid or liquid mixture using a solvent, and the subsequent evaporation of the solvent. An example of the extraction process, in the solid – liquid arrangement, is the process of brewing tea or coffee.
Coffee brewing in an espresso machine is a type of extraction in which a solvent (hot water – liquid) is added to a solid (ground coffee beans) in order to dissolve one or more components.
The flavors contained in coffee diffuse from the beans into water (the extractant).
*The extraction time when preparing espresso should be approximately 25 seconds. During this time, the cup should be filled with approx. 25–30 ml of the infusion created after the passage of water through 7 g (1 portion) of ground coffee.
Hot water increases the dissolution rate of the components to be extracted. In the espresso machine, a filtration stage takes place after the extraction stage.

Chromatography is used to purify and identify substances. This method of analysis of mixtures is used in biological research, pharmaceuticals manufacturing and many other fields. The name chromatography comes from the Greek chromos meaning „colour”. The first application of this method allowed to separate natural vegetable dyes, e.g. green – chlorophyll, yellow – xanthophil, orange – carotene.

• Mixtures can be separated using various techniques.

• Separation methods depend on the type of mixture and they use the properties of its components.

• Methods for separating homogeneous mixtures include chromatography.

• In order to separate certain mixtures, several techniques must be used. When separating the mixture of rock‑salt and chalk, we should (in turn): dissolve the mixture in water (rock‑salt dissolves), filter it (the chalk will remain on the filter), evaporate the filtrate (rock‑salt remains).

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Extraction and chromatography as a methods of separating and identifying mixtures

Extraction consists in washing desired components out of a solid or liquid mixture using a solvent, and the subsequent evaporation of the solvent. An example of the extraction process, in the solid – liquid arrangement, is the process of brewing tea or coffee.
Coffee brewing in an espresso machine is a type of extraction in which a solvent (hot water – liquid) is added to a solid (ground coffee beans) in order to dissolve one or more components.
The flavors contained in coffee diffuse from the beans into water (the extractant).
*The extraction time when preparing espresso should be approximately 25 seconds. During this time, the cup should be filled with approx. 25–30 ml of the infusion created after the passage of water through 7 g (1 portion) of ground coffee.
Hot water increases the dissolution rate of the components to be extracted. In the espresso machine, a filtration stage takes place after the extraction stage.

Chromatography is used to purify and identify substances. This method of analysis of mixtures is used in biological research, pharmaceuticals manufacturing and many other fields. The name chromatography comes from the Greek chromos meaning „colour”. The first application of this method allowed to separate natural vegetable dyes, e.g. green – chlorophyll, yellow – xanthophil, orange – carotene.

• Mixtures can be separated using various techniques.

• Separation methods depend on the type of mixture and they use the properties of its components.

• Methods for separating homogeneous mixtures include chromatography.

• In order to separate certain mixtures, several techniques must be used. When separating the mixture of rock‑salt and chalk, we should (in turn): dissolve the mixture in water (rock‑salt dissolves), filter it (the chalk will remain on the filter), evaporate the filtrate (rock‑salt remains).