The unbalanced half reactions for the lead-acid battery are: PbO_2(s) + HSO_4^-(

Question

The unbalanced half reactions for the lead-acid battery are: PbO_2(s) + HSO_4^-(aq) rightarrow PbSO_4(s) E_cell degree = 1.69 V Pb(s) + HSO_4^-(aq) rightarrow PbSO_4(s) E_cell degree = -0.37 V the oxidation half-reaction is (1 or 2) _______, the reduction half-reaction is _______ write the complete and balanced redox reaction under acidic conditions (indicate charges, states, etc, ) the oxidant is _______, the reducing agent is _______ the oxidation number of the metal element in the oxidant is _______, the oxidation number of the metal element in the reducing agent is _______, the oxidation number of the metal element in the products is ______ the standard cell potential of the lead acid battery is: E_cell degree = _______ V

Explanation / Answer

1)PbO2 +HSO4-   ----> PbSO4
2) Pb + HSO4-   ----> PbSO4

a) the oxidation half reaction is 2
the reduction half reaction is 1

b) PbO2 +HSO4-   + 3H+ + 2e- ----> PbSO4 + 2H2O. ( reduction reaction)
Pb + HSO4-   ----> PbSO4 + H+ + 2e- ( oxidation reaction)
Overall reaction is
Pb + PbO2 + 2H2SO4 ----> 2 PbSO4+2 H2O

C) the oxidant is PbO2
The reducing agent is Pb

d) the oxidation number of the metal element in the oxidant is +4
the oxidation number of the metal element in the reducing agent is zero
the oxidation number of the metal element in the product is +2

e) the standard potential of the lead acid battery is
Ecell= E (reduction half) - E ( oxidation half)
   = 1.69-(- 0.37)
   =2.06 Volts

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