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Science and Technology K–6 · Year 6

Rusting steel wool: what it needs and how much air it uses

Science understanding: Chemical sciences

PracticalLow risk

The idea

Rusting is an irreversible change in which iron combines with oxygen and water to form a new substance, so steel wool rusts only when both are present, rusts faster with salt, and uses up the oxygen in the air around it.

What you need

  • soap-free steel wool, grade 0 or 00, torn into 6 pieces of about 1 g
  • 5 small glass jars with lids, labelled
  • tap water, salty water (1 teaspoon of salt in 100 mL), white vinegar and cooking oil
  • tap water boiled and cooled by the teacher (boiling drives out dissolved air)
  • a silica gel sachet from packaging, for the dry jar
  • a clear tube closed at one end, about 15 cm long (a test tube), and a tall glass of water
  • a ruler reading to 1 mm, a marker pen, rubber gloves and safety glasses

How to do it

  1. Part A. Set up five jars, each with 1 g of steel wool: dry with the silica gel sachet and lid on; half covered in tap water; half covered in salty water; half covered in vinegar; fully covered in boiled and cooled water with a 1 cm layer of oil poured on top.
  2. Observe each jar every day for 5 days. Rate the rust from 0 (none) to 4 (orange all over) and take a photo.
  3. Part B. Rinse 1 g of steel wool in vinegar then water, and push it, still wet, to the closed end of the tube.
  4. Turn the tube upside down into the glass of water so a column of air is trapped above the water. Mark the water level and measure the length of the air column.
  5. Measure the air column again after 3 days and after 7 days, without lifting the tube out of the water.
  6. Work out the percentage by which the air column shrank, and compare it with the percentage of oxygen in air.
  7. Explain why the steel wool cannot be turned back again, and why steel bridges are painted or galvanised.

What you should see

Part A: the salty-water and vinegar pads rust first and most, orange-brown within a day or two; the tap-water pad shows rust in about two days, as Primary Connections notes for steel wool; the dry jar and the oil-sealed boiled-water jar stay grey. Rusting needs both water and oxygen, and salt speeds it up. Part B: water climbs the tube as the oxygen is used. Dry air is 20.95 percent oxygen by volume, so when all of it has reacted the air column shortens by about one fifth: a 10.0 cm column becomes about 7.9 cm, and the RSC method runs over two lessons about a week apart for this reason. The orange-brown rust is a new substance; drying, cooling or scraping never turns it back into steel wool.

What changes

What you change
conditions in each jar (dry, water, salty water, vinegar, water without air)
What you measure
amount of rust after 5 days; air column length in Part B
What you keep the same
  • mass and grade of steel wool
  • jar size
  • temperature
  • days

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

  • Rust is dirt on the surface that can be wiped off to leave the metal as it was.
  • Iron rusts in water alone (the oil-sealed jar of airless water shows oxygen is also needed).
  • Air is mostly oxygen.

Safety card

Low riskLearners carry it out

Hazards

  • steel wool splinters
  • vinegar in eyes
  • glass jars and tubes

Controls

  • rubber gloves when handling steel wool
  • safety glasses when pouring vinegar
  • plastic tubes where available
  • the teacher boils the water

Note

Household chemicals only. Risk assessment before the lesson using the NSW Department of Education Chemical Safety in Schools package (CSIS 1.7 Risk Assessment) or Primary RiskAssess.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

  • Science and Technology K-6 Syllabus (2017), current, taught until 2026; code read from the syllabus document on 22 September 2026ST3-6MW-SST3-7MW-TST3-1WS-S
  • Science and Technology K-6 Syllabus (2024), implemented from 2027; NESA's timeline is 2026 plan and prepare and 2027 start teaching, and schools may choose to implement it during 2026; code read from the outcomes page on 22 September 2026ST3-PQU-01ST3-DAT-01
  • Australian Curriculum v9AC9S6U04AC9S6H02AC9S6I02AC9S6I03AC9S6I04

Sources

The pages the author read to write this activity.

  1. www.scootle.edu.au/ec/search?accContentId=AC9S6U04
  2. curriculum.nsw.edu.au/learning-areas/science/science-and-technology-k-6-2024/outcomes
  3. www.nsw.gov.au/education-and-training/nesa/curriculum/science/science-and-technology-k-6-2017
  4. primaryconnections.org.au/teaching-sequences/year-6/chemistry-kitchen/lesson-7-really-rusty
  5. edu.rsc.org/experiments/how-much-oxygen-is-used-when-iron-wool-rusts/453.article
  6. edu.rsc.org/experiments/what-causes-iron-to-rust/434.article

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