Look at this iron nail. Outside, old metal gates and bike chains often turn a dusty orange-brown. What do you think is happening to the metal, and can that change ever be undone?
Today we will catch a new gas in a balloon, set up nails to watch over the coming days, and sort changes into ones we can undo and ones we cannot.
Some changes can be undone. Melting ice can be frozen again. The orange-brown on an old bike chain does not turn back into shiny metal.
Other changes stick: you cannot get the starting materials back the way they were. What clues might tell us a brand-new material has appeared?
We will mix baking soda with vinegar and trap whatever forms in a balloon. We will also put clean nails into three different places: dry air, water, and oil.
What do you think will happen to the balloon, and which nail do you think will change most over the coming days? Say why.
Write your balloon prediction and your nail prediction on your Investigation Journal page now, before we start the mix.
In your group you will mix baking soda and vinegar so any new gas is caught in a balloon.
- The powder is already in the balloon. Pour about 50 ml of vinegar into the bottle.
- Stretch the balloon neck over the bottle mouth without tipping the powder in yet.
- Lift the balloon so the powder falls in. Hold the bottle on the tray.
- Watch closely: what do you see, hear and feel?
Can you get the dry powder and vinegar back afterwards?
One person holds the bottle steady. Do not taste anything. Keep vinegar away from eyes.
As a group, decide which piece of evidence you will use first to judge that a new material has formed (for example the fizz, the balloon filling, a smell, or a change you can feel). Be ready to share that choice.
Straight after your run, jot two quick observation notes or a tiny sketch on your Investigation Journal page while the fizz is fresh in your mind. We will tidy the full conclusion later.
Rusting is slow, so we set it up today and watch it over the coming days. First wipe trays and wash or dry hands so oil and vinegar do not mix into the jars.
As a class we will prepare three clean nails in three labelled jars (one shared set is enough). Help with the steps on the board:
- Dry: place one clean nail in an empty dry jar or on a dry lid.
- Water: stand one nail in a jar with enough tap water to wet only part of the metal. Leave the jar open or only loosely covered so air can still reach the wet nail.
- Oil: stand the third nail in its jar and pour cooking oil until the whole nail is fully under the oil.
Remind yourself what you predicted for the nails. You will test that prediction on later jar checks when we look for a new orange-brown material on the metal. We are not expecting rust to appear in this lesson.
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