Pigment Research Authors: Jiří Škoda, Pavel Doulík, PF UJEP Ústí nad Labem, Czech Republic. years

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1 9-11 years Science Content: Elementary Chemistry Target Concepts/Skills: Colour, pigment, mixture, organic nature, green plant pigment, experiment Target Age group: 9-11 years Resources: School chalk; Brown felt pen; Denatured alcohol (ethanol) Small glass bowl or cup Stopwatch Coloured pencils An alternative method can include the use of filter paper/thick kitchen towel and water. Duration of activity: 90 minutes Summary: Pupils, on the basis of their own experimentation and observation. In the first inquiry activity involves the children testing whether a brown feltpen consists of one or more separate colours through the use of chromatography. Childre will learn that many pigments known from everyday life consist of a mixture of several basic colours. The gained knowledge can then be further applied to detailed investigation of plant pigments (chlorophylls, xanthophylls, carotenes), which are involved in photosynthesis. Objective: By the end of the activity children should be able to: Split mixtures of colour in the separate individual colours; Use observations of experiment outcomes to determine the pigments present in colour; Determine the composition of plant pigments in leaves. Pigment Authors: Jiří Škoda, Pavel Doulík, PF UJEP Ústí nad Labem, Czech Republic The content of the present document only reflects the author s views and the European Union is not liable for any use that may be made of the information therein.

2 1. Engage (Forming hypotheses) The teacher: Formulates problem questions such as: Why do plant leaves turn yellow in autumn? Afterwards, the pupils under the teacher s supervision carry out an experiment - separation of felt pen pigment. The teacher arranges a virtual experiment for the pupils (separation of plant pigments), and asks the students to try it out. The teacher coordinates and motivates the pupils to find answers to the problem questions set by her. The pupils: Implement the actual experiment of separation of simple pigments. They also observe the virtual experiment, discuss possible conclusions within their group (e.g.: How did the felt pen pigments separate? What colours does the felt pen contain? Are the colours obtained the same for all the groups? What pigments have we observed during the virtual experiment?). On the basis of their own experimentation and observation the pupils draw their own conclusions, which they further confront with other pupils and revise based on teacher s inquiring. 2. Inquiry (Designing and running experiments and observations) The pupils inquire whether pigments are formed by a single colour, or whether they consist of a mixture of several colours. Based on this, pupils formulate a hypothesis: Felt pen pigment consists of only one colour or indicate different colours. The pupils then verify the hypothesis by carrying out a real experiment in the group - the chromatographic separation of brown felt pen pigment on chalk. A simpler alternative method consists of using filter paper and water. The pupils identify the separate colours, which jointly form a brown pigment of the felt pen and through discussion within the group they revise their initial hypothesis. The pupils discover that the pigments can be a mixture of different colours, which will be further verified. The pupils then observe a virtual experiment of plant pigments separation using the chromatography method. Based on the previous experience they formulate another hypothesis, that the green pigment of plants is a mixture of different colours. During the virtual experiment where the separation of plant pigments (chlorophyll a, chlorophyll b, xanthophylls, and carotenes) takes place, the pupils confirm their hypothesis. During the final discussions they should be able to answer the initial problem question - leaves turn yellow because carotene and xanthophylls dominate in the plant pigment. 3. Evaluation The major ascertainment of the carried out activity is the fact that some pigments known to pupils from everyday life can be a mixture of several different colours. This finding will allow the pupils to become familiar with simple separation methods, both through direct experimentation, and actual observation. Based upon teaching science as inquiry (Carin et al., 2005) ; Inquiry-based science instruction What is it and does it matter? (Minner et al., 2009) ; the psychology of teaching Scientific Thinking: implications for science teaching and learning. (Li, Klahr, 2006)

3 TEACHERS GUIDE: Separation of brown pigment on chalk Can pigments consist of more simple colours? Resources: school chalk Brown felt pen (alcohol based) Denatured alcohol (ethanol) small glass bowl or cup Alternative method (filter paper/thick kitchen roll) and water Instructions for teachers: Paint a strip with the brown felt pen all around the surface of the chalk stick about 2 cm above the bottom of the chalk. Pour some ethanol, up to about cm in the small glass bowl (Petri dish) or a glass cup. Place the Chalk vertically into the bowl with ethanol the brown strip down. The strip must not be dipped in alcohol! Observe the course of the experiment. As soon as the head of mobile phase (wetting of the chalk) reaches about 1 cm below the top edge of the chalk, the chalk has to be removed from the ethanol and let dry. The experiment, however, can be terminated earlier, when the separation of the pigment in single colour components is sufficiently evident. If it is difficult to get hold of chalk and ethanol (surgical spirit), the experiment can be done but making a dot at the centre of a filter paper or kitchen roll, and then drop water onto it with a pipette. Notes and tips: The experiment can be carried out in groups of 4 to 5 pupils. It is best to use a simple cheap alcohol based brown felt pen/ or water-based felt pen for filter paper. The separation of the pigment in single colour components is sometimes possible with black felt pen but it depends on the type of pigment used in the felt pen. It is necessary to try it out first! The separation of the pigment on chalk takes approximately 15 minutes depending on the type of chalk/ but feel free to use other colours too. Brown pigment should be separated into 4-5 simple colours depending on the type of the felt pen.

4 SOLUTION The task problem solution process Pupils know pigments from everyday life. They commonly use coloured pencils, crayons, felt pens, watercolours, tempera paints, etc. Individual pigments seemingly contain only one colour. Pupils, based on their own experience do not realize that pigment can be made up of several simpler component colours. With the use of alcohol the brown pigment painted by felt pen on chalk can be separated. The course of the experiment looks like this: At the beginning after 5 minutes after 10 minutes after 15 minutes The brown pigment separates in the course of the experiment into a few single colours. Brown pigment separates into 5 different pigments. Did the brown pigment in my felt pen consist of 5 simple colours? Final stage - What and how we learned from the experiment? Alcohol dissolves the brown pigment of the felt pen and the individual colours, from which it is composed, are released. Brown pigment of the felt pen dissolves in alcohol. Brown pigment of the felt pen separates into 5 simple colours with the use of alcohol The alcohol rises up on the chalk and carries with it individual components of brown pigment. Brown pigment consists of these simple colours: pink, red, yellow, green, blue Pigment may consist of more simple colours. Many natural pigments (such as pigments in plants) consist of multiple colour components.

5 WORKSHEET: Can pigments consist of more simple colours? Instructions: Paint a strip with the brown felt pen all around the surface of the chalk stick about 2 cm above the bottom of the chalk. Pour a little of ethanol to the bottom of the glass bowl. The level of alcohol should reach about 1.5 cm above the bottom of the bowl. Stand the chalk into the bowl with ethanol (as shown in the picture). The painted strip must not be dipped in the ethanol! Start the stopwatch; After 5 minutes from the start of time recording, copy - draw what the chalk looks like using coloured pencils or take a photo of your stick; After 10 minutes from the start of time recording, draw again what the chalk looks like using coloured pencils Repeat this after 10 and 15 minutes. What pigment(s) are you using for your experiment? Write down what you think is going to happen to the brown colour.

6 Draw what the chalk looks like, using coloured pencils. At the beginning after 5 minutes after 10 minutes after 15 minutes What happened to the brown pigment during the experiment? How many colours was the brown pigment separated to? How many colours make up the brown pigment in your felt pen? What and how have we learned from the experiment?