ChemistryHiranyagarbha · Class 11-12
Corrosion ek chhoti si electrochemical cell hai
Ek hi loha ki plate par jang kuch jagah se hi shuru kyun hoti hai, aur paani ki boond ke neeche kyun badhti hai?
Socho pehle… phir dekho jawab
Kyunki satah par ek chhoti galvanic cell ban jaati hai: ek hissa anode (jahan loha oxidise hota hai) aur doosra cathode (jahan oxygen reduce hota hai), aur paani electrolyte ban kar aayon ko chalata hai.
Mechanism: anode par Fe → Fe²⁺ + 2e⁻. Cathode par (oxygen aur paani wale hisse mein) O₂ + 2H₂O + 4e⁻ → 4OH⁻. Electrons loha ke andar anode se cathode tak bahte hain, aur paani mein ghule aayon se circuit poora hota hai. Fe²⁺ aage oxygen se oxidise hokar hydrated Fe₂O₃·xH₂O, yaani jang, banta hai.
Kaaran aur gati: namak (NaCl) paani ki conductivity badhata hai, isliye samudri ilaake mein corrosion tez hota hai. Satah par khurach, impurity ya stress wale hisse anode ban sakte hain. Kai baar jang wahan se shuru hoti hai jahan oxygen kam hota hai (jaise paani ki boond ka beech ka hissa).
Cathodic protection: standard electrode potential E°(Fe²⁺/Fe) = −0.44 V aur E°(Zn²⁺/Zn) = −0.76 V. Zinc zyada negative hai, isliye zinc anode banta hai aur pehle ghulta hai, loha cathode ban kar bachta hai. Isliye galvanised loha ki parat khurach jaaye tab bhi bachav chalta hai; ship aur pipeline par zinc ya magnesium ke 'sacrificial anode' lagaye jaate hain.
Trade-off: rang sasta hai par sirf barrier hai (parat tooti toh jang neeche phailti hai); galvanising mehnga par damage mein bhi bachav deta hai; stainless steel lambe samay ke liye par kaafi mehnga; sacrificial anode ko samay-samay par badalna padta hai.
Ghar pe try karo
Ghar ya school ki teen loha ki cheezein (jaali, gate, balti) dhoondo. Har ek ke liye likho: kaun sa bachav lagaya gaya hai (rang, tel, zinc, stainless) aur uska ek faayda aur ek kamzori.
Wow!
Kai baar jang wahan se shuru hoti hai jahan oxygen kam hota hai — jaise paani ki boond ke beech mein!
3 sawaal
- Corrosion ki chhoti cell mein loha kis electrode ki tarah kaam karta hai jahan woh oxidise hota hai?
Jawab dekho
Anode. Oxidation anode par hota hai: Fe → Fe²⁺ + 2e⁻.
- Zinc loha ko sacrificial protection kyun deta hai?
Jawab dekho
Zinc ka E° loha se zyada negative hai, isliye woh pehle oxidise hota hai. E°(Zn²⁺/Zn) = −0.76 V, jo E°(Fe²⁺/Fe) = −0.44 V se zyada negative hai, isliye zinc anode banta hai.
- Samudri ilaake mein corrosion tez kyun hota hai?
Jawab dekho
Namak paani ki conductivity badhata hai. Namak (NaCl) paani ki conductivity badhata hai, jisse electrochemical cell tezi se kaam karti hai.
NCERT se jodo: NCERT Class 12 Chemistry — electrochemistry (corrosion ek electrochemical prakriya ke roop mein)