irreversible changes: chemical reactions - ansto changes: chemical reactions ... - 20cm of magnesium...

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Irreversible changes: Chemical reactions – Teacher notes

Irreversible changes: Chemical reactions Teacher notes

- Elephant toothpaste

- Volcano

- Magnesium ribbon

Australian Curriculum relevance: Year 6

Science Understanding: Chemical sciences

- Changes to materials can be reversible, such as melting, freezing, evaporating; or irreversible, such as burning and rusting (ACSSU095)

Science Inquiry Skills

- With guidance, pose questions to clarify practical problems or inform a scientific investigation, and predict what the findings of an investigation might be (ACSIS232)

- With guidance, plan appropriate investigation methods to answer questions or solve problems (ACSIS103)

- Decide which variable should be changed and measured in fair tests and accurately observe, measure and record data, using digital technologies as appropriate (ACSIS104)

- Use equipment and materials safely, identifying potential risks (ACSIS105)

- Construct and use a range of representations, including tables and graphs, to represent and describe observations, patterns or relationships in data using digital technologies as appropriate (ACSIS107)

- Compare data with predictions and use as evidence in developing explanations (ACSIS221)

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Elephant toothpaste

Materials

- Two plastic measuring jugs

- Large glass beaker

- 100mL 3-5% hydrogen peroxide (H2O2)

- 1 tsp yeast powder

- 50mL dishwashing detergent

- A funnel

- Tissues

- Safety goggles

- Warm water

- Plastic gloves

- Spoon for stirring

Method

1. Put on the safety goggles and plastic gloves.

1. Pour the whole peroxide bottle contents into one plastic jug with about 50mL of

dishwashing liquid. Stir gently.

2. In one plastic jug, stir one level teaspoon of dry yeast powder in 100mL of warm tap

water, until as much as possible dissolves.

3. Using the tissues as filter paper inside the funnel, filter the yeast solution into the other

plastic measuring jug to remove any large undissolved chunks of yeast.

4. Rinse the empty plastic jug and pour in the whole peroxide bottle contents plus about

50mL of dishwashing liquid. Stir gently.

5. Holding both plastic jugs at the same time (one in each hand), pour the contents

simultaneously into the large glass beaker. Watch as the mixture begins to froth and erupt

slowly from the mouth of the beaker.

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Clean up

- The chemicals used are non-toxic to the environment. Dispose of all liquids and wash all

containers and equipment in the sink.

- Clean up any spills with water and paper towels

- Avoid hydrogen peroxide contact with skin and eyes. Thoroughly wash any skin exposed to

hydrogen peroxide with water.

Suggested discussion points

1. What did each of the liquids look like before they were combined?

2. What happened when the liquids from the two separate jugs were mixed together?

3. Do you think this change is reversible or irreversible? Could we easily separate the froth in

the beaker back into the liquids originally in each plastic jug?

4. This is an irreversible chemical reaction. The hydrogen peroxide is split into water and

oxygen gas, and the yeast solution makes this chemical reaction happen very quickly.

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Volcano

Materials

- 3 large beakers

- 1x 500m conical flask

- Two teaspoons

- Citric acid in glass container

- Sodium Bicarbonate in a glass container

- Large tray to capture overspill

- Large jug of water

- A pair of rubber gloves

- Safety glasses

- Protective clothing (lab coat or an old shirt)

- Red and blue food colouring

Method

1. Put on the safety glasses, plastic gloves and either a lab coat or an old shirt.

2. Lay large tray onto a flat surface. Place 500ml conical flask in middle of tray.

3. Add 3 teaspoons of sodium bicarbonate and three drops of red food colouring with

300ml of water in the conical flask. Swirl the flask to mix.

4. Mix 3 teaspoons of citric acid with 200ml of water and 3 drops of blue food colouring

into the 500ml beaker.

5. With the appropriate level of drama pour the blue citric acid solution as quickly as

possible into the conical flask containing the red sodium bicarbonate solution. It

should blow back enough to look like it exploded.

Clean up

- The chemicals used are non-toxic to the environment. Dispose of all liquids and wash all

containers and equipment in the sink.

- Clean up any spills with water and paper towels

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1. What did each of the liquids look like before they were combined?

2. What happened when the liquids from the two separate jugs were mixed together?

3. Do you think this change is reversible or irreversible? Could we easily separate the froth in

the flask back into the liquids originally in each plastic jug?

4. This is an irreversible chemical reaction. The citric acid reacts with the sodium

bicarbonate to produce carbon dioxide gas.

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Magnesium ribbon

Materials

- Portable gas stove or hot flame source

- Pliers or chemistry tongs

- 20cm of magnesium ribbon

- Lab coat

- Flame-retardant gloves

- Tinted sunglasses

Method

1. Put on a lab coat, flame-retardant gloves and sunglasses.

2. Hold the ribbon as shown below using the pliers.

3. Ignite the end of the ribbon in the gas stove. Continue holding the ribbon as it burns.

NOTE: Hold the ribbon at about a 20° dip to allow the flame to preheat the unburnt

ribbon ahead of it. The flame will go out if the ribbon is held horizontally.

NOTE: Do not to look directly at the burning magnesium, as it could damage your

eyes.

Clean up

- Once the magnesium ribbon has stopped burning and has cooled down, dispose of it in the

bin.

- The flame can be quickly extinguished with water if required.

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1. What did the magnesium ribbon look like before it burned?

2. What did the magnesium ribbon looked like after burning?

3. Do you think this change is reversible or irreversible?

4. This is an irreversible chemical reaction. The citric acid reacts with the sodium

bicarbonate to produce carbon dioxide gas.

irreversible changes: chemical reactions - ansto changes: chemical reactions ... - 20cm of magnesium...

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