Corrosion of Metal

Question 1

Factors that speed up rusting

Answer 1

1. Presence of acidic pollutants
   → speed up: promotion of Fe2+
2. Presence of ionic compounds
   →e.g. sea water: Mobile ions→ rusting faster
3. High temperature
   → ↑rate of reaction
   e.g. car exhaust pipes
4. Attachment to less reactive metals to iron
   → Fe loses e- more readily
   e.g. Tin
5. Scratched, bent or shap area of an iron-made object

Question 2

Rust indicator

Answer 2

1. Potassium hexacyanoferrate(III) solution
→K[Fe(CN)6](aq)
→ presence of Fe2+
2. Phenolphthalein
→ presence of OH-
3. NaCl(aq)
→ catalyst?

Question 3

Equation for rusting(3 parts)

Answer 3

Fe(s)→ Fe2+(aq) + 2e-
O2(g) + H2O(l) + 2e- → 2OH-(aq)

1. Fe2+(aq) + 2OH-(aq) →Fe(OH)2(s)
2. 4Fe(OH)2(s) + O2(g) + 2H2O(l) → Fe(OH)3(s)
3. Fe(OH)3(s) → Fe2O3•H2O(s)

Overall:
4Fe(s) + 3O2(g) +2nH2O(l) → 2Fe2O3•nH2O(s)