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A secondary cell after use can be recharged by passing current through it in the opposite direction so that it can be used again. A good secondary cell can undergo a large number of discharging and charging cycles. The most important secondary cell is the lead storage battery commonly used in automobiles and invertors. It consists of a lead anode and a grid of lead packed with lead dioxide (PbO 2 ) as cathode. A 38% solution of sulphuric acid is used as an electrolyte. The cell reactions when the battery is in use are given below: Anode: Pb(s) + SO 4 2– (aq)----> PbSO 4 (s) + 2e – Cathode: PbO 2 (s) + SO 4 2– (aq) + 4H + (aq) + 2e – ----> PbSO 4 (s) + 2H 2 O (l ) i.e., overall cell reaction consisting of cathode and anode reactions is: Pb(s) + PbO 2 (s) + 2H 2 SO 4 (aq)---> 2PbSO 4 (s) + 2H 2 O(l) On charging the battery the reaction is reversed and PbSO 4 (s) on anode and cathode is converted into Pb and PbO 2 , respectively.

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Electrochemistry

Short Answer Type

241. How is an electrode potential measured?

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242. Write a Nernst equation for the half-cell reaction: Mⁿ⁺(aq) + ne^– → M(s)

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243. Write the Nernst equation for a galvanic cell corresponding to the reaction:

Zn (s) + {Cu}^{2 +} (aq) \to Zn (aq) + Cu (s)

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244.

Electrolysis of molten NaCl gives sodium at cathode while aqueous NaCl gives H₂ gas at cathode.

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245. What is dry cell? Explain its working.

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246. Draw curves to show how the molar conductance of strong electrolytes varies with dilutions.

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247. How the Kohlrausch’s law is used to determine the degree of ionization of weak electrolyte?

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248. For the cell Zn/Zn²⁺ (aq) || Cu²⁺(aq) | Cu, derive the relation between E°_cell and K_c at 298 k.

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249. For the standard cell, Cu(s) | Cu²+(aq) || Ag⁺ (aq) | Ag(s)
Given: E° _Cu²⁺/Cu = 0.34V, E° = 0.80V
(a) Identify cathode and anode as the current is drawn through the cell.
(b) Write the reactions taking place at the electrodes.
(c) Calculate the standard cell potential.

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250. What do you mean by a secondary cell? Discuss the function of lead storage battery.

A secondary cell after use can be recharged by passing current through it in the opposite direction so that it can be used again. A good secondary cell can undergo a large number of discharging and charging cycles. The most important secondary cell is the lead storage battery commonly used in automobiles and invertors.
It consists of a lead anode and a grid of lead packed with lead dioxide (PbO₂ ) as cathode. A 38% solution of sulphuric acid is used as an electrolyte.
The cell reactions when the battery is in use are given below:

Anode: Pb(s) + SO₄^2–(aq)----> PbSO₄(s) + 2e^–
Cathode: PbO₂(s) + SO₄^2–(aq) + 4H⁺(aq) + 2e^– ----> PbSO₄ (s) + 2H₂O (l )

i.e., overall cell reaction consisting of cathode and anode reactions is:

Pb(s) + PbO₂(s) + 2H₂SO₄(aq)---> 2PbSO₄(s) + 2H₂O(l)

On charging the battery the reaction is reversed and PbSO₄(s) on anode and cathode is converted into Pb and PbO₂, respectively.

114 Views