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Electrochemistry

Short Answer Type

181. Write the Nernst equation and emf of the following cells at 298 k.
Mg(s) | Mg²⁺ (0.001 M) || Cu²⁺ (0.0001 M) | Cu(s)

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182. Write the Nernst equation and emf of the following cells at 298 k.
Fe(s) | Fe²⁺ (0.001 M) || H⁺ (1M) | H₂ (g) (1 bar) | Pt(s)

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183. Write the Nernst equation and emf of the following cells at 298 k.
Sn(s) | Sn²⁺ (0.050 M) || H⁺(0.020 M) H₂(g) (1bar) Pt (s)

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184. Write the Nernst equation and emf of the following cells at 298 k.
Pt(s) | Br₂ (l) | Br^– (0.010 M) || H⁺ (0.030 M) | + H₂(g) (1 bar) | Pt(s).

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185. What is corrosion? What are the factors which affect corrosion?

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186. CO₂ is always present in natural water. Explain its effect (increases, stops or no effect) on rusting of iron.

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187. Rusting of iron is quicker in saline water than in ordinary water. Explain.

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188. We can use aluminium in place of zinc for cathodic protection of rusting. Comment.

In cathodic protection the metal (here iron) to be protected from corrosion is connected by a wire to a more anodic matal ( like Al, Zn etc), so that all the corrosion occurs at this more active metal. Thus the parent metal is protected while the more active metal gets corroded slowly.
As the standard electrode potential of aluminium is more than that of zinc so Al is more anodic than Zn.
Thus we can better use aluminium in place of zinc for cathodic protection of rusting of iron.
At anode : Al → Al³⁺ + 3e^–At cathode : O₂ + 2H₂O + 4e^– --->4OH^–

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