This investigation is designed to show which conditions are needed for iron to rust. Three clean iron nails are placed in the tubes shown in Fig. 1. Tube A ...
Question 1 Report
This investigation is designed to show which conditions are needed for iron to rust. Three clean iron nails are placed in the tubes shown in Fig. 1. Tube A contains dry air because calcium chloride absorbs water vapour. Tube B contains boiled water with a layer of oil, preventing oxygen from the air dissolving in the water. Tube C contains both air and water. After one week, an orange-brown solid is seen only on the nail in tube C.
The result helps explain why damp air in the atmosphere can damage steel structures.
(a) State the colour of the solid formed on the nail in tube C. [1]
(b) Which tube contains oxygen but no water, and which tube contains water but no oxygen? [2]
(c) Explain how the results from all three tubes show the conditions required for rusting. [3]
(d) Name the gas from air that is needed for rusting. [1]
(e) Complete the word equation.
iron + ______ + ______ → hydrated iron(III) oxide [3]
(f) Give two methods used to protect a bicycle's steel chain from rusting. [2]
(g) State why calcium chloride is used in tube A. [1]
Answer Details
(a) The solid is orange-brown (or brown). This is rust, hydrated iron(III) oxide. [1]
(b) Tube A contains oxygen but no water because calcium chloride keeps the air dry. Tube B contains water but no oxygen because boiling removes dissolved air and the oil layer prevents oxygen entering. [2]
(c) The comparison controls the conditions needed for rusting:
- Tube C contains both oxygen and water, and the nail rusts.
- Tube A contains oxygen but no water, and does not rust.
- Tube B contains water but no oxygen, and does not rust.
Therefore, rusting requires both water and oxygen. [3]
(d) The gas from air needed for rusting is oxygen. [1]
(e) iron + oxygen + water → hydrated iron(III) oxide. Hydrated iron(III) oxide is another name for rust. [3]
(f) Two suitable methods are oiling and greasing the chain. These form a barrier that prevents water and oxygen reaching the steel. Painting, plastic coating or galvanising would also be accepted. [2]
(g) Calcium chloride is used because it absorbs water vapour, keeping the air dry. [1]
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