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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).

For given cell Anode reaction:

2 {Br}^{-} (aq) \to {Br}_{2} (l) + 2 e^{-}

Cathode reaction:

2 H^{+} (aq) + 2 e^{-} \to H_{2} (g)

Overall cell reaction:

2 {Br}^{-} (aq) + 2 H^{+} (aq) \to {Br}_{2} (l) + H_{2} (g)

Here, n = 2,

{E^{0}}_{cell} = {E^{0}}_{cathode} - {E^{0}}_{anode} = 0 - 1.08 V = - 1.08 V .

The Nernst equation for E_cell and 298 k can be written as:

E_{cell} = {E^{0}}_{cell} - \frac{0.059}{n} \log \frac{[{Br}^{2 +}] [H_{2}]}{[{Br}^{-}] {[H^{+}]}^{2}} = 1.08 - \frac{0.059}{2} \log \frac{1}{[10^{- 2}]^{2} [3 \times 10^{- 2}]^{2}} = - 1.08 - 0.0295 [\log \frac{1}{10^{- 4} \times 9 \times 10^{- 4}}] = - 1.08 - 0.0295 (\log 10^{8} - \log 9) = - 1.08 - 0.0295 (7.0458) = - 1.08 - 0.2078 = - 1.2878 V .

The negative value of E_cell indicates the cell has been arranged in a reverse way, i.e., hydrogen electrode will act as anode and bromine electrode act as cathode. The cell should be represented as Pt | H₂ (1 bar), H⁺ (0.03 M) || Br (0.01 M) | Br₂(l), Pt

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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.

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189. How is cathodic protection of Iron different from its galvanisation?

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Long Answer Type

190. Define conductivity and molar conductivity for the solution of an electrolyte. Discuss their variaion with concentration.

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