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Electrochemistry

Short Answer Type

251. Define conductivity and molar conductivity for the solution of an electrolyte.

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252.

On the basis of the standard electrode potential values stated for acid solution. Predict whether Ti⁴⁺ species may be used to oxidise Fe^II to Fe^III.
Reaction: E°/V Ti^IV + e^– → Ti³⁺ + 0.01
Fe³⁺ + e^– → Fe²⁺ + 0.77

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253. What are fuel cells? Write the electrode reactions of a fuel cell which uses the reaction of hydrogen with oxygen.

A device to convert chemical energy of fuel into electrical energy is called fuel cell.

Hydrogen-oxygen fuel cell: The cell consists of three compartments separated from one another by porous electrode. The hydrogen gas is fed into one compartment and the oxygen gas is fed into another compartment. These gases then diffuse slowly through the electrodes and react with an electrolyte that is in the central compartment. The electrodes are made of a conducting material, such as graphite, with a sprinkling of platinum to act as a catalyst, and the electrolyte is an aqueous solution of a base. The reactions are

Cathode: O₂(g) + 2H₂O(l) + 4e^–-----> 4OH^–(aq)
Anode: 2H₂ (g) + 4OH^–(aq)-----> 4H₂O(l) + 4e^–
Overall reaction being:

2H₂(g) + O₂(g) ----->2H₂O(l )

Advantages: (i) Fuel cells are efficient and free from pollution.
(ii) The only product in the reaction of fuel cell is water which can be removed and the astronauts of a spacecraft can drink it.

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254.

Predict the products of electrolysis obtained at the electrodes in each case when the electrodes used are of platinum.
(i) An aqueous solution of AgNO_3.(ii) An aqueous solution of H₂SO₄.

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Long Answer Type

255. Define the following terms: (i) Cathodic protection, (ii) Electrochemical series, (iii) Cell constant, (iv) Equivalent conductivity, (v) Strong and weak electrolytes.

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256. Explain the working of galvanic cell. How does the electrochemical cell differ from electrolytic cell?

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Short Answer Type

257. What is normal hydrogen electrode? Discuss its uses.

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Long Answer Type

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

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259. Distinguish between: (a) Electrolytes and non-electrolytes, (b) Reduction potential and oxidation potential (c) Primary cells and secondary cells, (d) Specific conductivity and molar conductivity.

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260.

The conductivity of 0.01 M solution of acetic acid at 25°C is 1.63 x 10^–4 s cm^–1. Given:
Λ°_m (HCl) = 426 s cm² mol^–1, Δ°_m (Na AC) = 91.5 cm² mol^–1Λ°_m (NaCl) = 126.5 cm² mol^–1Calculate:
(a) the molar conductivity of acetic acid
(b) the degree of dissociation of acetic acid.
(c) the dissociation constant.
(d) the pH of 0.01 M solution of acetic acid.

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