New Zealand Science Teacher

Nature of science activity

15/04/2012

The following Nature of Science (NoS) activities use colour chemistry and have a focus on ‘Participating and Contributing in Science’. 

By Pru Casey, Otago Boys’ High School, and Steven Sexton, University of Otago

Background

In 2010, the NZCER was commissioned to write a paper, Inspired by Science that in part encouraged debate on student engagement with science. The report stated that an understanding of science is becoming increasingly important. This was further developed in another report entitled, Primary science education for the 21st century: How, what, why? In the second report it was argued that primary science is one way to nurture children’s interest in the world around them and as a result help develop their positive attitudes towards science. The following activities have been developed for primary teachers to pick up and use them as a means to engage children’s interest in their world through the NoS strand of Participating and Contributing in Science.

Colour Chemistry

Colour Chemistry, based around literacy texts, enables teachers to incorporate real world science activities within a literacy programme. While these texts are often used in junior primary classrooms, they are also springboards for upper primary students to explore these activities. The activities have a Material World focus through the Participating and Contributing strand of the NoS. By understanding that scientists can use colour as ‘identifiers’, or indicators, they can be found in the world all around us! Raisins, plum skins, tea, pumpkin and red cabbage are used as a means to help sort ‘things’ into groups. For example, we can use indicators to sort substances into acids, bases or neutrals. Acids are typically sour, such as: lemons, vinegar, and Coca-Cola. Bases generally taste horrid and are often slimy, like: soaps, baking soda, and urea. Neutral items are neither an acid nor base, for example egg whites.

Activity 1: Lunch (primary students)

This activity is built around Dr. Seuss’s book entitled: Green Eggs and Ham. This primary age student activity enables younger students to link words such as acid/ acidic, base/basic and neutral to their world through their lunches, while older students should be given the opportunity to build on their discoveries and discuss changes that could be made to their food choices.

Begin by investigating the items in your lunch box and finding out more about the foods you like, e.g. are they acid or base? We tend to put acids on any food that is too basic. Ever wondered why you like tomato sauce on sausages, or why your parents like mint on lamb, or why lemon goes well on fish? What is on your lunch to make it taste better? Here is how we can show what in your lunch is acidic, basic or neutral.

First, we have to make Cabbage Water Indicator. Take a handful of red cabbage and put in a food processor, add 1-2 cups of boiling water (be careful!). Let this sit for a minute and then process for about 30 seconds to 1 minute. Using a strainer, pour the cabbage/water mixture into a bowl. The water in the bowl is what you will use as your ‘indicator.’ It is easier to use if you pour the cabbage water indicator into a plastic squeeze bottle for the rest of these activities.

The leftover chopped up cabbage is compost material. Now using an icetray, take small pieces of your lunch and place them in the icetray cavities. Remember to leave three spots empty for later. You might want to label the pieces of food to remember what you put in. Now squeeze the cabbage water indicator onto the pieces of your food. What happens? What colour does the cabbage water indicator turn? Which do you think are acidic, basic or neutral?

Now, into the three empty cavities add lemon juice or vinegar to one, baking soda to another, and egg whites to the third. Add cabbage water. What colour does the cabbage water become when mixed with the acidic, basic or neutral food item? What does this tell you about the food in your own lunch box?

Note: At this point some students might need to repeat this activity to show which foods were acidic, basic or neutral.

So now we know egg whites are neutral and turn green when cabbage water indictor is used; do you think you would like green eggs and ham? What might they taste like? To make green eggs, just add the yolk to the egg whites and cabbage water and they can be fried as in the book. If you scramble them, the colour will change, as now you are mixing green with a yellow/orange colour which makes pale/lime green. Surprisingly, the taste does not alter that much.

Activity 2: Sherbet (upper primary students)

This activity is built around Dr Seuss’s character The Yink in, One Fish Two Fish Red Fish Blue Fish. This activity is a taste test and might not be suitable for younger students due to the very strong reactions they may have to the ingredients.

You will need four of these five ingredients: icing sugar, raspberry drink concentrate, baking soda and either citric or tartaric acid. Three of these look very similar. Have the four ingredients in four separate containers labelled A, B, C and D. Clean Petri dishes work well but so do plates or bowls.

Students then use a clean Popsicle stick to transfer a small amount of each ingredient to their own ice cube trays. Note: Students could test each one by taste, but not everyone will like all four of these so be careful and have paper towels ready. Now using the cabbage water indicator students individually test to find out which are acids and bases.

(For younger students you may need to review the colours cabbage water turns in acids, bases and neutral items. A further link to real world activities is to discuss what the baking soda does in cooking, or why it is used in cooking.)

What did The Yink like to do? And what colour was this? What do you think will happen when we mix all four ingredients in a plastic cup and add water? Students can do this individually but it is better in groups of four as the ratio of ingredients should be ½ cup of icing sugar, ¼ cup of drink concentrate, 1 teaspoon of acid and 1 teaspoon of baking soda. The dry ingredients can be tasted before water is added. Remember to think pink like The Yink.

Here are some discussions that can build upon our Pink Sherbet. Just like our lunches where we tend to add acids to basic foods to make them taste better, why do we add sugar to drinks? Why do we add baking soda to our cooking? What happens when we mix all the ingredients together? What other drinks behave like our Pink Sherbet? What happens to the ingredients if we leave them sitting around? So what do you think would happen to the Pink Sherbet?

Activity 3: Chromatography (upper primary)

This activity is built around the Movie, Who Framed Roger Rabbit, or Scene of the Crime in the Choices series.

Scientists use colour to track small particles, and the size of particles can be investigated using chromatography. Small particles ‘run’ quickly in water and larger particles ‘run’ more slowly. This is a physical property. You can use the food colouring from M&Ms (avoid peanut centred ones due to possible nut allergies and Smarties don’t work as they have natural colourings that do not easily separate in water).

This process, called chromatography, is the same principle that CSI use to separate out sizes of DNA fragments when we want to know, Who Framed Roger Rabbit with evidence or ‘DNA’ from the Scene of the Crime.

You will need the following materials for this: M&Ms, paint brushes, filter paper cut into 5cm strips about 2-3cm wide and rolled up to form a circle, plates with a small amount of water to stand the filter strips in; it is important that not too much water be used; the filter paper rings only need to sit in the water.

Take a set of M&Ms so that pairs of students have one of each colour. Using the brush, dip into water and wipe off some of the colouring of the M&M and then paint this onto a rolled up strip of filter paper. You should paint just below the centre line of the paper strip as the colours will run up the paper as the filter paper absorbs water. It is critical that the painted on M&M colour is not submerged into or in contact with the water as the colour will then diffuse into the water. Set onto a plate of water and watch what happens. What happens to the different colours of the M&Ms? What is green or brown?

Final thoughts

Participating and Contributing in Science allows students to link what they are doing in the classroom to their world. For younger students, activities such as these allow students to relate the science to their world. For upper primary students, these activities can be springboards for further discussions around food choices, or how we are able to use everyday items to explore forensic science.

And in line with the NZCER report, as discussed above, primary science needs to build on the experiences children bring to school. What better way than through the food they eat? Students using these simple activities are then able to not only relate the literacy texts to the classroom science, but also to their world. Thus, teachers are able to provide students with a range of engaging activities centred on purposeful classroom talk.

For further information contact: steven.sexton@otago.ac.nz