A steel garden fork is left outdoors for a whole winter. By spring it is covered in a flaky solid that is the everyday sign of rusting on iron and steel. Wh...
Question 1 Report
A steel garden fork is left outdoors for a whole winter. By spring it is covered in a flaky solid that is the everyday sign of rusting on iron and steel. What colour is this rust most likely to be?
Answer Details
Rust is hydrated iron(III) oxide, \( \mathrm{Fe_2O_3}\cdot x\mathrm{H_2O} \), and it is orange-brown. Because the iron(III) oxide holds water loosely, the solid is porous and flaky, so it lifts off and lets fresh iron underneath be attacked. That is why a whole fork can eventually corrode through rather than being sealed by its own coating.
Silvery-white is the appearance of the clean steel itself, not the corrosion product. Bright green is the colour associated with copper corroding on old roofs, and with iron(II) compounds in solution. Deep blue points to copper(II) compounds. Learn the classic colours for the iron oxidation states: iron(II) species are usually pale green and iron(III) species are orange or red-brown.
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