Question

2. Some moist iron wool was placed in a test tube and the tube was inverted and set up as shown below. y cm (ii) x cm The apparatus was left for one week. The water level

rose and iron wool turned red-brown. (i) Write the chemical equation to show the rusting of iron. (1 mark) Write the expression for an approximate percentage. (1 mark)​

Answer 1

Rusting of iron involves the formation of hydrated iron(III) oxide, and the chemical equation is 4 Fe(s) + 3 O₂(g) + 6 H₂O(l) → 4 Fe₃O₄ · nH₂O(s). For the percentage of rust caused by corrosion, compare the initial and final mass of iron wool.

Step-by-step explanation:

When iron corrodes, it reacts with oxygen and water to form hydrated iron(III) oxide, commonly known as rust. The chemical equation for the rusting of iron can be represented as:

4 Fe(s) + 3 O₂(g) + 6 H₂O(l) → 4 Fe₃O₄ · nH₂O(s)

Here 's' stands for solid, 'g' for gas, and 'l' for liquid. The 'n' in the product represents the variable number of water molecules in the hydrated iron oxide.

For the approximate percentage of rust, one can measure the changes in mass of the iron wool before and after rusting and use the following expression:

Percentage of rust = (Mass of rust - Mass of original iron wool) / Mass of original iron wool × 100%

Note that the percentage can only be calculated if the mass is measured before and after the reaction.