ChemixaLEARN CHEMISTRY

What makes nails rust

Objective: test which conditions cause iron nails to rust by exposing them to different environments for several days. You will set up controls, observe changes daily, and explain the results with oxidation and electrochemistry.

Safety:

Nails are sharp: handle carefully and keep them away from small children. Do not use galvanized or coated nails, which can flake. Adult supervision is required for minors. Dispose of rusty nails in household trash, not where bare feet walk.

Materials

  • 4 plain iron nails (not galvanized)
  • 4 small jars or cups
  • Water
  • Table salt
  • Cooking oil
  • Labels and pen
  • Paper towels

Procedure

1

Label the test jars

Label four jars: dry air, plain water, salt water, and oil-coated.

2

Set the dry control

Place one nail in the dry jar with nothing else.

3

Prepare water and salt water

Cover the second nail with plain water and the third with water plus a spoonful of dissolved salt.

4

Oil-coat the fourth nail

Coat the fourth nail in cooking oil, then place it in its jar with no water.

5

Wait and observe daily

Leave all jars undisturbed for 5 to 7 days, checking and photographing the nails daily.

6

Rank and conclude

Rank the nails from most to least rusted and write your conclusion.

What to observe

  • The nail in dry air shows almost no change after a week.

  • The nail in plain water develops orange-brown spots.

  • The nail in salt water rusts the most and the fastest.

  • The oil-coated nail stays shiny and rust-free.

Why it happens

Rusting is the oxidation of iron in the presence of oxygen and water, an electrochemical process with tiny anodes and cathodes on the nail's surface. Iron atoms lose electrons (oxidation) while oxygen gains them (reduction), and the product is hydrated iron(III) oxide, Fe2O3·xH2O, the familiar reddish-brown rust. The nail in dry air barely changes because water is missing; the nail in plain water rusts slowly; the nail in salt water rusts fastest because dissolved ions improve electrical conductivity between the anodic and cathodic regions. The oil-coated nail resists rust because the oil blocks both water and oxygen from reaching the metal, which is exactly how protective coatings work on bridges and cars.

Try variations

  • Test vinegar instead of salt water and compare the speed.

  • Try a nail half in water and half in air to find where rust starts.

  • Check whether warming the jars changes the rusting rate.