iGCSE Chemistry (0620) Core:9.5 Corrosion of metals: Exam Style Questions Paper 1- New Syllabus
▶️ Answer/Explanation
Detailed solution:
Rusting of iron requires both water and oxygen. In tube P, a drying agent (anhydrous calcium chloride) absorbs all moisture, so there is no water present. Without water, rusting cannot occur, and no oxygen is consumed, so the water level remains unchanged. In tube Q, water is present along with air, so rusting takes place. Rusting consumes oxygen from the air, reducing the pressure inside the tube, and as a result, water from the beaker rises up the tube.
▶️ Answer/Explanation
Detailed solution:
For iron to rust, it needs both water (or moisture) and oxygen. Looking at the conditions: test-tube 1 has an iron nail exposed to air and water, so rusting will definitely happen. Test-tube 2 has water that has been boiled to remove dissolved air, and it’s covered with a layer of oil to prevent more air from getting in, so there’s no oxygen available and rusting won’t happen. Test-tube 3 has a drying agent that removes all moisture from the air, so there’s no water present and no rusting can occur. Only test-tube 1 provides both essential ingredients for rust formation.
▶️ Answer/Explanation
Detailed solution:
Rust is specifically hydrated iron(III) oxide. It requires both oxygen and water to form, so it includes water molecules in its structure (hydrated). The iron is in the +3 oxidation state (iron(III)), not iron(II). The terms “anhydrous” (without water) or “iron(II)” are therefore incorrect for rust.