Rust needs air and water
Iron rusts only when it meets both.
The brown nail
Leave an iron nail outside for a few days and it grows a brown deposit. But is it the air, or the water, or both that does it?
Three iron nails are kept for a week. A: dry air only. B: water only (no air). C: air and water together. Which nail grows the brown deposit?
What this lesson covers
The idea
Iron develops a brown deposit called rust only when in contact with both air and water (moist air); the formation of rust on iron objects is called rusting.
The brown nail
Leave an iron nail outside for a few days and it grows a brown deposit. But is it the air, or the water, or both that does it?
Three iron nails are kept for a week. A: dry air only. B: water only (no air). C: air and water together. Which nail grows the brown deposit?
- Only the nail in A
- Only the nail in B
- Only the nail in C
- All three nails
Three tubes, one week
Slide the days forward to about day 6. Then tap each tube to see what was inside it.
Rust and rusting
Iron develops a brown deposit only when it is in contact with both air and water (moist air). This brown deposit is called rust, and its formation on iron objects is called rusting.
Air alone is not enough. Water alone is not enough. It takes both together.
- Tube | What the nail had | After a week
- A | air only (no water) | shiny, no deposit
- B | water only (no air) | shiny, no deposit
- C | air and water together | brown deposit
Notes
Iron gets a brown deposit called rust only when it is in contact with both air and water (moist air). Forming rust is called rusting.
Check yourself
The brown deposit that forms on iron is called...
An iron nail is kept for a week with dry air only. What do we see?
Out of the three tubes A, B and C, in how many did the iron nail rust?
Answer: 1 tube
Only the nail in tube C, which had both air and water, grew rust. A had no water and B had no air.
Which iron object is the most likely to rust?
- rust — correct. Yes! And the process of its formation is called rusting.
- lustre. Lustre is the shine of a metal.
- sonority. Sonority is the ringing sound of a metal.
- Brown rust. Rust needs water too. Dry air alone is not enough.
- No brown deposit — correct. Yes! With no water, the nail stays shiny.
- The nail melts. Nothing like that happens.
- A nail sealed in a jar with a drying agent. The drying agent soaks up water, so there is only dry air.
- A nail in boiled water with oil poured on top. Boiling drives out the air and the oil keeps air away. So it gets only water.
- An iron gate left outside in the rain — correct. Yes! Rain and air together make moist air.