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Viatouch
Teacher Articles
Teacher Created Materials
Separating Colours
by Elizabeth Klein
| Subject: |
Science |
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| Grade Level: |
Middle School |
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| Objectives: |
To observe changes when mixing primary colours
To separate colours using a simple form of chromatography
To write a detailed explanation about one of the experiments |
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| Time Needed: |
One hour at each table |
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| Materials: |
cellophane, colour pencils, blue and yellow paints, recording sheet, compass, scissors, three flashlights, rubber bands, paper towels, newspaper, coffee filter, blotting paper, inks, felt-tip pens, pegs, dish for water, food colouring, salt, wire, washing detergent, shampoo, shower gel, computers, glass prisms |
Instructions:
White light can be split into separate colours—red, orange, yellow, green, blue, indigo and violet. Together, they are known as the spectrum. Some colours are mixtures of other colours. These can also be split using a process called chromatography.
Organise the class into three groups. The following science experiments can be set up by the teacher at each table before the lesson. Have the students to complete each experiment, documenting each outcome. When all of the experiments are completed, ask the students to write an explanation on one of the activities, and include labelled drawings.
Suggestion prior to commencement: The teacher should spend some time demonstrating what the students are expected to achieve.
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Table One
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1)
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Take red, blue and yellow squares of cellophane and place two different colours on top of each other, for example: red on blue or red on yellow. Record the new colour created. |
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Try to see how many colour combinations students can create by using just blue and yellow paints by varying the amounts used. Have them try to paint a sheet of squares with as many different shades as possible. |
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Table Two
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| 1) |
Encourage each student to make a circle from a sheet of cardboard with a compass and scissors. Ask the students to choose two primary colours (red and yellow, or red and blue, or blue and yellow) Then have them to make dots with the two colours all over their circle using felt-tip pens. Ask the students to push a pencil through the middle and spin it on the table. The colours should merge together to form another distinct colour. Record the observation. |
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Ask the students to cut another circle and divide it into seven equal segments. Ask them to colour each segment in a colour of the spectrum. When they spin this circle, the colours should merge and form white. |
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Table Three
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Have the students to cut strips from paper towels and draw a single dot about 3cm from the bottom of each with felt-tip pens. Use blue, red, black and green. Then hang the paper over the edge of a dish of water so that only the bottom 1cm is touching the water and not the ink. Peg it to the lip of the dish so that it doesn't fall in. Observe what happens to the inks. As the paper soaks up the water, different colours "bleed" from the original. This is called chromatography. Try using green, black and brown food colouring instead of ink and different paper—newspaper, coffee filter, blotting paper. |
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Change the property of the water by adding salt. Use different amounts to see what happens. The colour won't climb up so far.
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Extra Activities:
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Darken a corner of the room. Fasten a red sheet of cellophane to a flashlight with a rubber band. Do the same with a blue sheet and a green sheet of cellophane and two flashlights. Shine them onto a white wall so that the filtered beams overlap. Have the students observe carefully how light mixes to form lighter colours, unlike paints that make darker colours when mixed. The red and blue overlap should form magenta, and the green and blue should form cyan.
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Research Sir Isaac Newton, who discovered that white light was made up of different colours. He passed sunlight through a narrow slit and projected the spectrum created onto a wall using a glass prism.
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Research chromatography and Michael Tswett, the Russian biologist who developed chromatography.
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Research capillary movement, which explains how sponges soak up water and how water travels up to the leaves in plants.
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Observe the refraction of white light through a glass prism.
Elizabeth Klein was a primary school teacher for nineteen years and is now a freelance writer. She lives in Sydney, Australia, with her husband.
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