Write the cell reactions which occur in lead storage battery (i) when the battery is in use and (ii) when the battery is on charging. from Chemistry Electrochemistry Class 12 Nagaland Board
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Class 10 Class 12
Write the cell reactions which occur in lead storage battery (i) when the battery is in use and (ii) when the battery is on charging.

(i) The cell reactions during the use (discharge) of lead storage battery are:

The cell reactions when the battery is in use are given below:

Anode: Pb(s) + SO42-(aq)   PbSO4 + 2e-

Cathode:PbO2(s) + 4H+(aq)  + SO42-(aq)  PbSO4(s) + 2H2O(l)

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

Pb(s) +PbO2 +4H+(aq) +SO42-(aq)  2PbSO4(s) + 2H2O(l)

ii) Recharging a lead-acid cell:

  • is a non-spontaneous redox reaction (E(redox) is negative), that is, an electrolytic process
  • requires an input of slightly more than 2 volts per cell to drive the spontaneous reactions in the reverse direction
  • converts electrical energy back into chemical energy which is stored in the lead, lead dioxide and sulfuric acid in the cell
The cell reaction is:
At Anode:
PbSO4(s) + 2e-  Pb(s) +SO42-(aq)At Cathode:PbO2(s) + 2H2O(l) PbSO4 +SO42-overall net reaction 2PbSO4(s) + 2H2O(l) Pb(s) +PbO2(s) +4H+ (aq) +2SO42-



2781 Views

Can you store copper sulphate solutions in a Zinc pot?

Answer:

No. Because zinc is more reactive than copper and thus holes will be developed in zinc pot.

Cu2+(aq) + Zn(s) → Zn2+ (aq) + Cu(s)
1384 Views

Consult the table of standard electrode potentials and suggest three substance that can oxidize ferrous ions under suitable conditions.

Answer:


oxidation of ferrous ion means :

Fe2+--> Fe3+ +e-EFe3+Fe2+0 = 0.77V
Any substance which standard electrode potential is more than that of Fe+3 /F+2 can oxidise ferrous ions. 
(refer to the table given in book)

The EMF of the substance whose reduction potentials greater than 0.77V will oxidised ferrous ion.
for example Br2, Cl2,and F2 .

879 Views

How would you determine the standard electrode potential of the system Mg2+/Mg?

Answer:

Use standard hydrogen electrode as anode and Mg2+ | Mg as a cathode we can measure the standard electrodepotential of systemMg2+ | Mg. Standard hydrogen electrode, represented by Pt(s), H2(g) (1 atm) | H+ (aq) and dip the electrode of Magnesium wire in a 1M MgSO4 solution .The standard hydrogen electrode is always zero.
Use formula
Eocell = Eo right  – Eoleft
The standard hydrogen electrode is always zero.
So that the value of
Eoleft =0
Hence
Eocell = Eo Mg|Mg2+
Or
Eo Mg|Mg2+= Eocell
2203 Views

Calculate the emf of the cell in which the following reaction takes place:
Ni(s) + 2Ag+ (0.002 M)  Ni2+ (0.160 M) + 2Ag(s)
Given that EoCell = 1.05 V

Answer:

Ni(s)+2Ag+(aq)Ni2+(aq)+2As(s)
Ecell = Eocell + RT2FlnAg+(aq)2Ni2+ (aq)
or      Ecell = Eocell+0.0592 logAg+(aq)2Ni2+ (aq)
 
The equation is also written as

or    Ecell = Eocell-0.0592logNi2+(aq)Ag+ (aq)2         = 1.05 V - 0.0295 log 0.1600.002  

= 1.05 V – 0.0295 x log 80

= 1.05 V – 0.0295 x 1.9031

= 1.05 V – 0.056 = 0.99 V.

1585 Views

Calculate the potential of hydrogen electrode in contact with a solution whose pH is 10.

Answer:

For hydrogen electrode, ,
given that      pH = 10
use formula [H+] = 10–pH
so that  [H+] = 10−10 M
Electrode reaction will
H+  + e –  →1/2 H2
Use the formula


EH+/H2  = EoH+/H2 - RTnFlnH2[H+]2              = 0-8.314×2982×96500ln IH+2              = 0.05915 log [H+]              =-0.05915 pH             =-0.05915 × 10 =- 0.59 V
1279 Views