Rockets, rust, and one very dirty handful of change.
Slide 02 — What we already know
A rocket needs two things
Fuel burns. But it can only burn if something brings the oxygen. In space there's no air to borrow from — so the rocket carries its own.
FuelHydrogen
+
OxidizerOxygen
→
What's leftWater
Slide 03 — The rocket's exhaust
Water?
H2O
Hhydrogen — the fuel
Ooxygen — the oxidizer
2two hydrogens, one oxygen
The fuel and the oxidizer are both still there. They just joined up and became one new thing.
Hydrogen oxide
we call it water — but that's its real name
Slide 04 — The rule
Oxygen joins onto things. Then we rename them.
the thing+oxygen=the thing's name, then oxide
Oxide is the word we stick on the end to say oxygen joined this. Hear the “ox” hiding in it? That's oxygen, still in the name.
copper + oxygen = copper oxide
iron + oxygen = iron oxide
you already know this one by its nickname
What do we normally call iron oxide?
Rust. The everyday word tells you nothing. The science name tells you exactly what's in it.
Slide 05 — Our pennies
So what's on these pennies?
The metalCopper
+
From the airOxygen
→
The dull stuffCopper oxide
It isn't dirt sitting on top. The copper on the surface became something else. The penny is wearing a thin coat of a different substance.
Hold up a dull penny and a shiny one — which one has more copper in it?
The same. Some of the dull one's copper is just wearing a disguise.
Slide 06 — The question
How do we get the shine back?
Undo the reaction — pull the oxygen back off
Leave it alone and wash the copper oxide away
Which one do you think would be easier?
Slide 07 — Meet the bath
Salt has a real name too
sodium + chlorine = sodium chloride
the thing, then what joined it — same rule as before
Chlorine joined onto sodium, so we renamed it. Not an oxide this time — oxygen isn't the only thing that joins on.
Vinegar is an acid. It does the loosening. The salt makes it much better at the job. Neither one changes — until they reach the penny.
Slide 08 — Do it
Pennies in.
The acid and the chloride team up and dissolve the copper oxide. The dull coat lifts off and floats away — and the shiny copper underneath was there the whole time.
enough vinegar to cover, a big spoonful of salt
as many as we've got — we need the water loaded
watch the water, not just the pennies
When these come out: dry one penny, leave one wet. Set them side by side.
Slide 09 — Where did it go?
The copper didn't vanish.
It's in the cup. Spread out so finely you can't see it.
How could we prove there's copper in that water?
Slide 10 — The swap
Some metals are grabbier than others
GrabbierIron
↔
Less grabbyCopper
→
ResultThey trade places
Put an iron nail in copper water and the iron pushes in and takes the copper's spot. Iron goes into the water. The copper has nowhere to go but onto the nail.
It only works one way. Put a copper penny in iron water and nothing happens — copper isn't grabby enough to push iron out.
Slide 11 — Do it
Nail in.
Give it a few minutes. Then look at the nail — and remember it started out gray.
plain steel, sanded shiny — not galvanized
straight into the used penny water
coppery in minutes, convincing in twenty
We moved copper off a penny, through water, and onto a nail — without touching either one.
Slide 12 — One last trick
Two pennies. Same bath. Different endings.
still bright
blue-green already
In the car it took years to go dull. This took an hour. We did two things to it:
we stripped off the coat that was protecting it
we left the bare copper sitting in salt water
Oxygen on its own is slow. Oxygen plus water is fast — and salt makes it faster still.
Slide 13 — Proof, in our kitchen
Same pan. Only water changes.
sits in the cupboard for years — fine
left in the sink overnight — rusted by morning
Same iron. Same air. Same oxygen the whole time. The only difference is the water.
So why do we rub oil on a cast iron pan?
To keep water off the iron. The oil does the same job the dull coat was doing on the penny — it's a lid.
Slide 14 — What we learned
The name tells you what's inside
something joined up with oxygen
iron + oxygen — we call it rust
copper + oxygen — the dull coat on a penny
hydrogen + oxygen — we call it water
Rockets, rust, and pennies — and water is what decides how fast it happens.