What it does
Iron and steel slowly turn into flaky reddish-brown rust. This page is a safe, fast version of the classic test-tube experiment that finds out what rusting needs. Six clean iron nails sit in six tubes:
- A. Dry air: a corked tube with calcium chloride to soak up moisture. Air, no water.
- B. No air: boiled water (which has lost its dissolved air) under a layer of oil. Water, no air.
- C. Air and water: ordinary tap water, open to the air.
- D. Salt water: the same, with salt dissolved in it.
- E. Painted: a painted nail in tap water.
- F. Galvanised: a zinc-coated nail in tap water.
Drag the day slider or press Watch 3 weeks and rust spots grow on the nails that can rust. The results table fills in with yes/no for air and water and how much rust there is. Tick Scratch the coated nails to see the big difference between paint and zinc: the painted nail rusts where the paint is broken, while the galvanised nail stays clean because zinc, being more reactive than iron, corrodes first (sacrificial protection).
A second card gives the equation for rust and works out the mass of iron(III) oxide made from any mass of iron, showing that a rusted nail gets heavier.
It fits the Class 10 science chapters on chemical reactions (corrosion, an effect of oxidation) and on metals and non-metals (corrosion and how to prevent it). Rusting is a redox reaction you can sort in the reaction type sorter; why zinc protects iron comes from the reactivity series lab.
How to use it
- Look at the six tubes on day 0: six shiny nails.
- Drag the slider from day 0 to day 21, or press Watch 3 weeks (press again to pause). Back to day 0 starts again.
- Read the results table: tube, air, water, and how much rust (as a description and a percentage of the surface).
- Tick Scratch the coated nails and watch tubes E and F.
- In the second card, type a mass of iron to see the mass of rust it makes.
The speeds are a teaching model with made-up rates. Real nails vary with temperature, the steel used and how clean they are, but the pattern is the one you would see in a school lab.
A worked example
At day 7 in the model, nail C (air and water) has some rust over about 39% of its surface and nail D (salt water) is covered (about 75%). Nails A, B, E and F have none. By day 21, C is at 77% and D at 99%.
The rust card starts with 5.6 g of iron: 5.6 ÷ 55.845 = 0.1003 mol of iron, which makes half as many moles of Fe₂O₃, 0.05014 mol. Multiplying by its molar mass of 159.687 g/mol gives 8.007 g of iron(III) oxide. The extra 2.407 g is oxygen taken from the air. Iron is 69.94% of Fe₂O₃ by mass.
Check yourself
Four fresh questions each time: which of two nails rusts first, the mass of rust from a mass of iron (with Fe = 56 and O = 16), the oxidation number of iron in rust, and whether a rusted nail is heavier. Nothing is saved.
FAQ
Why does boiled water need oil on top? Boiling drives out the air dissolved in water. Without the oil, air would dissolve back in within hours and the nail would rust.
Is rusting the same as corrosion? Rusting is the corrosion of iron. Other metals corrode too: silver goes black, copper goes green. Aluminium forms a thin oxide layer that protects it.
Why does salt speed it up? Salt makes the water conduct electricity better, which helps the electron-transfer reactions of rusting. That is why cars rust faster where roads are salted and why ships need extra protection.
Is this from the NCERT book? It covers the same topic with fibub’s own pictures and wording. fibub is not part of NCERT.
Where the numbers come from
- The conditions for rusting, the effect of salt, and protection by paint and galvanising are general chemistry facts as taught in school, written fresh for fibub. The rusting speeds are made-up teaching values.
- Masses use IUPAC 2021 standard atomic weights (Fe 55.845, O 15.999). Checked against hand calculation: 5.6 g of iron gives 8.007 g of Fe₂O₃.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.