Teaching Sequence

5 minutes - Tune in: A sting in the tail – Chemical reactions in First Nations peoples treatment of stingray venom.
30 minutes - Find out: Chemical reactions in baking damper and First Nations bread baking
10 minutes - Take action: Which other chemical reactions do you think First Nations peoples have significant knowledge in? How might we use their knowledge?
5 minutes - Reflection: I used to think…..I now think…..

Tune in: A sting in the tail – Chemical reactions in First Nations peoples treatment of stingray venom

Step 1.

Ask the students if they lived in a time before modern medicine had been created, how would they treat someone who had received a burn, cut or sting? Show the images on slide 2 of the attached PowerPoint to the class and guide students through a discussion. The images show a stingray and the venomous barb it possesses on its tail and a Wurakinni plant.

Explain to students that in the Tiwi Islands (Islands North of Darwin), the leaves of this plant, Tiwi name Wurakinni, Latin name Ipomoea pes-caprae, were heated on hot rocks and then applied as a poultice (see image below and teacher content information) to relieve the pain from a stingray barb (Tiwi name Kirluwarringa).

Stingray with a barbed tail

Primejyothi, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Wurakinni Plant

Step 2.

Explain to students that in the Tiwi Islands (Islands North of Darwin), the leaves of this plant, Tiwi name Wurakinni, Latin name Ipomoea pes-caprae, were heated on hot rocks and then applied as a poultice (see teacher content information) to relieve the pain from a stingray barb (Tiwi name Kirluwarringa).

Note: An image of a poultice is provided on slide 3 of the attached PowerPoint

Use these prompts to conduct a brief class discussion to remind students of previous knowledge on reactions. (Suggested solutions to these questions can be found in the teacher content information.)

Why would the leaves be heated?
How do you think a poultice would work?
What does this tell you about the rate of reaction?
What chemical reaction might be involved? Synthesis, decomposition or displacement?

Find out: Synthesis, decomposition and displacement reactions in food–damper and First Nations bread baking

Step 1.

Display the following simple recipe for damper so students can see it. (Recipe can be found on slide 4 of the attached slide deck)

500g plain wheat flour (4 cups)
1 tablespoon baking powder
½ teaspoon salt
300ml of milk

Cooking instructions:

Mix dry ingredients in a bowl
Add wet ingredients
Knead the dough until stretchy
Bake in a hot oven

Guide discussion with students to discern what aspects of the recipe they can link with what they know about chemical reactions. Encourage students to annotate their thoughts on the worksheet. Answers are provided in the following steps.

Why do you think the recipe has baking powder?
Why do you think the mix needs to be kneaded?
What does the addition of milk do?

Step 2.

Explain to students that a part of this recipe involves a displacement reaction. You may like to ask a few quick questions for students to recall their knowledge of displacement reactions.

Explain to students that when making damper, baking soda is a necessary ingredient. Baking powder contains baking soda, (the base, sodium bicarbonate) and a dry acid (cream of tartar). When liquid is added to the recipe, these two ingredients undergo a displacement reaction to form bubbles of carbon dioxide gas which help the bread rise.

The reaction that occurs between sodium bicarbonate (NaHCO₃) and cream of tartar (KHC₄H₄O₆) is:

NaHCO₃ + KHC₄H₄O₆ → KNaC₄H₄O₆ + H₂O + CO₂

Ask Students to label where they can see the displacement occurring.

(the equation is already balanced. H in cream of tartar is replaced by Na)

Step 3.

Explain to students that part of this recipe involves a synthesis reaction. You may like to ask a few quick questions for students to recall their knowledge of synthesis reactions.

When liquid is added, and the dough is kneaded, two protein compounds in the wheat flour, gliadin and glutenin, undergo a synthesis reaction to form gluten C₂₉H₄₅N₅O₈. The kneading, or mixing, enables the gluten to form a network of chains and sheets that gives the bread its elastic-like structure. It helps dough rise by trapping the gas bubbles and water that are produced to make it moist and fluffy. A simple representation of the reaction between glutenin and gliadin to form gluten is provided on slide 5 of the attached PowerPoint.

Step 4.

Explain to students that a part of this recipe involves a decomposition reaction. You may like to ask a few quick questions for students to recall their knowledge of decomposition reactions.

Baking soda, or sodium bicarbonate (NaHCO₃), is a basic chemical that can undergo a decomposition reaction when heated. At temperatures above 80 degrees Celsius, sodium bicarbonate starts to break down into three compounds, forming sodium carbonate (Na₂CO₃), water (H₂O) and carbon dioxide (CO₂).

NaHCO_3(s) → Na₂CO_3(s) + H₂O_(g) + CO₂ _(g)

Ask the students to annotate the reaction on their worksheet, labelling what the two gaseous products would be responsible for in the making of bread. (When a gas is produced during baking it causes the dough to rise and gives texture)

Step 5.

Ask the students to refer to the recipe on their worksheet for the following type of Indigenous bread. This recipe can also be found on slide 6 of the attached slide deck. There are no ingredients in common with the damper, but we still get a similar product.

Spinifex flour has no gluten.
Spinifex flour is also slightly acidic
The acacia ash is basic.

The steps needed to make the bread are as follows.

Burn acacia wood, allow it to cool and collect the white ash
Collect spinifex seeds and grind them to make flour
Combine the spinifex flour with some of the ash and add water
Knead the dough
Bake in a campfire

Step 6.

Ask the students the following questions to gauge their understanding of the chemical processes in the Indigenous bread recipe

Why do you think the ash needs to be cool?
- To prevent any unwanted reactions when it is added to the dough - if the ash is hot, it might start to react with compounds in the dough - this could affect texture, taste and rise later on.
Why do the seeds need grinding?
- Humans can’t digest raw seeds. Grind to absorb nutrients and to break the hard seed husks to make flour which will be able to form a dough.
What does the addition of water do?
- Brings the flour together to form the dough

Step 7.

The following are reactions that occur during the process of making and baking the spinifex bread recipe. Ask students to classify the reactions as synthesis, decomposition or displacement. Solutions are provided below.

Notes:

H+ represents an acid of some type
If needed, you can give students some tips on discerning reaction types.
- Synthesis - Two compounds combine to make something new.
- Displacement - One element replaces another.
- Decomposition - One compound breaks down into two or more compounds.

Reactions in Recipe	Type of Reaction Synthesis, Decomposition, Displacement or none of the above
1	KOH + CO₂ → KHCO₃	Synthesis
2	KHCO₃ → K₂CO₃ + H₂O + CO₂	Decomposition
3	CaO + CO₂ → CaCO₃	Synthesis
4	CaCO_{3 (s)}+ 2H⁺ _(aq) → Ca²⁺ _(aq) + CO_{2 (g)} + H₂O _(l)	Acid-Base reaction

Step 8.

Even though the two recipes don’t have ingredients in common, we get a similar product because similar chemical reactions are occurring.

Ask students to determine the similarities and differences between the components of the Indigenous spinifex flour bread and damper using the Venn Diagram on their worksheets. Encourage them to use chemical concepts and consider how they affect the final product. The Venn diagram can also be found on slide 8 of the attached PowerPoint.

Step 9.

Show the students the images of damper and spinifex bread found on slide 9 of the attached PowerPoint and ask the following question

Both bread recipes produce gaseous products that help the dough to rise. How would the overall texture of the spinifex bread be different to the damper, and why?

Please refer to the Teacher Information Content for the suggested solution.

Take action: Which other chemical reactions do you think First Nations peoples have significant knowledge in? How might we use their knowledge?

Step 1.

Lead the students in a class discussion. Ask the students if they know of examples demonstrating First Nations peoples significant knowledge of chemical reactions. How might we use this knowledge in a modern context?

If there is time, you can encourage students to research these examples in small groups. Please refer to the teacher's content information for examples.

Reflection

This can be a short group discussion, or students can take notes using the following template for a deeper reflection. Read the following question and allow students to discuss or write down their responses in the worksheet. Encourage students to think about

What they knew at the start of the lesson,
What they still want to know to expand their knowledge
What they learnt and how this has affected their thinking

How has your understanding of First Nations chemistry shifted throughout this lesson?

First Nations Chemistry: Reactions in Food and Medicine

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