What it shows
Iron rusts when both water and air reach it. Coating a nail with oil, paint, nail polish, wax or petroleum jelly keeps them away. Comparing coated nails with a bare one over ten days shows which coating protects best and why painted gates and oiled tools last longer.
The science
Rust is hydrated iron oxide, formed when iron reacts with oxygen in the presence of water. Both are needed; a nail in dry air or in boiled, sealed water barely rusts. A coating that is continuous and does not let water through acts as a barrier, so no reaction can start underneath. Coatings that crack, wash off or soak up water fail first. This is the simplest kind of corrosion protection, used on gates, bridges and tools.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Six plain iron nails (not galvanised)
- Cooking oil, nail polish, candle wax (adult melts), petroleum jelly and a little poster paint
- Six small glasses or cut bottle bottoms
- Tap water
- Labels and a marker
- A magnifier
Safety
For this project: An adult must melt and handle the wax, and nail polish must be used in a ventilated room away from flames. Nails are sharp; carry them point down.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Clean all six nails with a dry cloth and label the glasses: bare, oil, polish, wax, jelly, paint.
Coat five nails fully, one with each material, and let the polish and paint dry for an hour; the adult dips one in melted wax.
Place each nail in its glass and add water to cover half the nail, so each has both wet and air-exposed parts.
Keep all glasses together in the same place so temperature and light are the same for all.
Look at the nails every day with the magnifier and write a score from 0 (no rust) to 5 (fully rusted) for each.
Note where rust appears first, usually at the water line on the bare nail.
After ten days lift each nail out, rub it on white paper and compare the orange marks.
Make a chart of rust score against day for all six nails and name the best coating.
What you should see
The bare nail shows rust within two or three days, mostly at the water line; wax, polish and paint keep their nails almost clean; oil and jelly protect partly until they wash off.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What two things are needed for iron to rust?
Oxygen from the air and water.
2Why does rust start at the water line?
Both air and water are present there in good supply.
3What is rust made of?
Iron oxide joined with water, a reddish brown flaky solid.
4Why do people paint iron gates?
The paint is a barrier that keeps water and air away from the iron.
Take it further
Scratch the paint on one coated nail and watch whether rust spreads under the coating from the scratch.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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