Rusting of iron — a tiny electrochemical cellलोहे पर जंग — एक छोटा विद्युत-रासायनिक सेलRusting of iron — a tiny electrochemical cell

NCERT Fig 2.13 · Class 12 Chemistry · Chapter 2 · interactive diagram

Parts and what they mean

• Anodic spot (oxidation) (ऐनोडी स्थान (ऑक्सीकरण)) — 2Fe(s) → 2Fe²⁺ + 4e⁻, E°(Fe²⁺/Fe) = −0.44 V.
• Cathodic spot (reduction of O₂) (कैथोडी स्थान (O₂ का अपचयन)) — O₂(g) + 4H⁺(aq) + 4e⁻ → 2H₂O(l), E° = 1.23 V. H⁺ is believed to come from H₂CO₃ (CO₂ from air dissolved in water) and other acidic oxides.
• Electrons move through the metal (इलेक्ट्रॉन धातु से होकर जाते हैं) — Overall: 2Fe(s) + O₂(g) + 4H⁺(aq) → 2Fe²⁺(aq) + 2H₂O(l), E°(cell) = 1.67 V.
• Rust — hydrated ferric oxide (जंग — जलयोजित फ़ेरिक ऑक्साइड) — Fe²⁺ is further oxidised by air to Fe³⁺, which comes out as rust, Fe₂O₃·xH₂O.
• Water drop (with dissolved CO₂, ions) (पानी की बूँद (घुली CO₂, आयनों सहित)) — Rusting needs both water and air.
• Oxygen from air (हवा की ऑक्सीजन) — Reaches the metal most easily at the edge of the drop.
• Iron object (लोहे की वस्तु) — Prevent rusting by paint or chemicals (e.g. bisphenol), by coating with other metals (Sn, Zn), or with a sacrificial electrode (Mg, Zn) that corrodes instead.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 2.13. Report a mistake