Question

The overall cell reaction occurring in an alkaline battery isZn(s) + MnO₂(s) + H₂O(l) → ZnO(s) + Mn(OH)₂(s) (e) In practice, voltaic cells of a given capacity (coulombs) are heavier than the calculation in part (c) indicates. Explain.(c) What is the total mass of reactants consumed in part (b)?(b) If 4.50 g of zinc is oxidized, how many grams of manganese dioxide and of water are consumed?

Answer 1

b) Mass of MnO₂ = 5.981 g

    Mass of H₂O = 1.2384 g

c) Total Mass of Reactant consumed = 11.708 g

b) Given Reaction

            Zn(s) + MnO₂(s) + H₂O(l) → ZnO(s) + Mn(OH)₂(s)

  Mass of Zn = 4.50 g

  Moles of Zn = 0.0688 moles

   Now,

    Moles of Zn = moles of MnO₂ = moles of H₂O = moles of ZnO = moles of                   Mn(OH)₂

Hence ,

Moles of MnO₂ = 0.0688 moles

Mass of MnO₂ = 0.0688 × 86.9368 g

                        = 5.981 g

Similarly,

    Moles of H₂O = 0.0688 moles

     Mass of H₂O = 0.0688 × 18 g

                           = 1.2384 g

c) now ,

    Moles of  ZnO = 0.0688 moles

     Mass of  ZnO  = 0.06880× 81.3794 g

                              = 5.598 g

 Moles of  Mn(OH)₂ = 0.0688 moles

  Mass of  Mn(OH)₂ =0.0688 × 88.952 g

                                  = 6.11 g

Total mass of Product = 11.708 g

Total Mass of Reactant = 11.715 g

Hence,

    Total mass of reactant consumed = 11.708 g

c)  As total mass of reactant is more than that of mass of reactant consumed , Hence G is more than that of mass of reactant consumed .

G = - nFEcell

 

and no. of moles of reactant  is greater than that of number of moles of reactant consumed .

       Hence voltaic cell of given Capacity are heavier than that of mass of reactant consumed .

 Thus from above conclusion we can say that , Mass of the reactant consumed is 11.708 g.

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