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Electrochemistry

Short Answer Type

91. What is the effect of an increase in the concentration of zinc ions on the electrode potential of zinc electrode for which E° equals – 0.76 V?

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92. What is a primary cell? Give an example.

148 Views

93. Express the relation between conductivity and molar conductivity of a solution.

149 Views

Long Answer Type

94. Explain with examples the terms weak and strong electrolytes. How can these be distinguished?

(i) Weak electrolytes : An electrolyte that ionizes partially in solution is called a weak electrolyte. The solution formed contains ions which are in equilibrium with un-ionised molecules, e.g., acetic acid dissolves in water to form H₃O⁺ and CH₃COO⁺ ion. The solution contains H₃O⁺(hydronium ion), CH₃COO^– (acetate ion) and unionised CH₃COOH molecules.

The degree of ionisation of a weak electrolyte is much less than 1. These have low values of molar conductivities at high concentration. Degree of ionisation and molar conductivity both increases with dilution.
(ii) Strong electrolyte : An electrolyte which is almost completely ionised in solution is called a strong electrolyte. The degree of ionisation of a strong electrolyte is 1 or 100% (or nearly so). The solution formed contains ions which are in equilibrium with solid form of strong electrolyte.

Strong electrolyte

Weak electrolyte

1. These have higher molar conductivities at all concentrations.

2. λ°_m values increase very slightly with dilution.

3. Degree of ionisation is very high at all concentration i.e., almost fully ionized.

4. Most of the salts like NaCl, KCl, NaNO₃, BaCl₂ and mineral acids like HCl, H₂SO₄, HNO₃ and NaOH, KOH etc are common examples of strong electrolytes

1. These have much lower conductivities at high concentration.

2. λ°_m values increase sharply with dilution.

3. Degree of ionisation is very low at high concentration and increases with dilution.

4. Salts like ammonium acetate, acetic acid, aq NH₄OH, aqueous CO₂ and organic acids and bases are common examples of weak electrolytes.

600 Views

95.

Predict the products of electrolysis in each of the following:
(i) An aqueous solution of AgNO₃ with silver electrodes.
(ii) An aqueous solution of AgNO₃ with platinum electrodes.
(iii) A dilute solution of H₂SO₄ with platinum electrodes.
(iv) An aqueous solution of CuCl₂ with platinum electrodes.

174 Views

96.

Depict the galvanic cell in which the reaction
Zn(s) + 2Ag⁺(aq) → Zn²⁺(aq) + 2Ag(s) takes place. Further show:
(i) Which of the electrode is negatively charged?
(ii) The carriers of the current in the cell.
(iii) Individual reaction at each electrode.

299 Views

Short Answer Type

97. Following two reactions can occur at cathode in the electrolysis of aqueous sodium chloride:
Na⁺ + e^– → Na(s) 2H₂O(l) + 2r → H₂(g) + 2OH^–(aq)
E°_red = – 0.83 V
Which reaction takes place preferentially and why?

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98. Iron does not rust even if zinc coating is broken in galvanized iron pipe. Explain.

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99. Explain why:
(i) E° for Mn³⁺/ Mn²⁺ couple is more positive than that Fe³⁺/Fe²⁺. (At. No. Mn = 25, Fe = 26).
(ii) Ce³⁺ can be easily oxidised to Ce⁴⁺ (At. No. Ce= 58).

583 Views

100. With the halp of ionic equations describe what happen: When
(i) pH of a solution of dichromate ions is raised.
(ii) Potassium manganate is electro-chemically oxidised.

266 Views