Question

In which case is iron corroded faster, if a protective coating is partly damaged:
a) tin- or zinc-plated iron?
b) chromium- or nickel-plated iron?
Explain your answer by writing down the equations of the cathodic and anodic reactions in acid, neutral and alkaline medium.

Answer 1

Answer on Question#49801- Chemistry, Other

Question:

In which case is iron corroded faster, if a protective coating is partly damaged:

a) tin- or zinc-plated iron?

b) chromium- or nickel-plated iron?

Explain your answer by writing down the equations of the cathodic and anodic reactions in acid, neutral and alkaline medium.

Answer:

a) Iron corrodes faster in case of tin-plated iron.

Fe – Sn

(-) Fe → Fe²⁺ + 2e; E°Fe = -0,440 V

(+) O₂⁰ + 2H₂O + 4e = 4OH⁻ (neutral and alkaline medium); E° = 0,401 V

(-) Fe → Fe²⁺ + 2e; E°Fe = -0,440 V

(+) 2H⁺ + 2e → H₂ (acid medium); E° = 0

Fe – Zn

(-) Zn → Zn²⁺ + 2e; E°Zn = -0,763 V

(+) O₂⁰ + 2H₂O + 4e → 4OH⁻ (neutral and alkaline medium); E° = 0,401 V

(-) Zn²⁺ + 2e → Zn; E°Zn = -0,763 V

(+) 2H⁺ + 2e → H₂ (acid medium); E° = 0 V

b) Iron corrodes faster in case of nickel-plated iron.

Fe – Cr

(-) Cr⁰ → Cr³⁺ + 3ē; E°Cr = -0,744 V

(+) 2H⁺ + 2e → H₂ (acid medium); E° = 0 V

(-) Cr⁰ – 3ē → Cr³⁺

(+) O₂⁰ + 2H₂O + 4e = 4OH⁻ (neutral and alkaline medium); E° = 0,401 V

Fe – Ni

(-) Fe → Fe²⁺ + 2e; E°Fe = -0,440 V

(+) O₂⁰ + 2H₂O + 4e = 4OH⁻ (neutral and alkaline medium); E° = 0,401 V

(-) Fe → Fe²⁺ + 2e; E°Fe = -0,440 V

(+) 2H⁺ + 2e = H₂ (acid medium); E° = 0

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