A galvanic cell Mn(s)|Mn^2 + (aq) || Co^2 + (aq)|Co(s) is constructed using a co

Question

A galvanic cell Mn(s)|Mn^2 + (aq) || Co^2 + (aq)|Co(s) is constructed using a completely immersed Mn electrode that weighs 26.9 g and a Co electrode immersed in 616 mL of 1.00 M Co^2 + (aq) solution. A steady current of 0.0552 A is drawn from the cell as the electrons move from the Mn electrode to the Co electrode. (a) Which reactant is the limiting reactant in this cell? Enter symbol (b) How long does it take for the cell to be completely discharged? S (c) How much mass has the Co electrode gained when the cell is completely discharged? g (d) What is the concentration of the Co^2 + (aq) when the cell is completely discharged? (Assume that the limiting reactant is 100% reacted.) M

Explanation / Answer

(a)

Moles of Mn = mass of Mn / MOlar mass of Mn = 26.9 / 55 = 0.489 mol

Moles of Co2+ = 1.00 * 616 / 1000 = 0.616 mol

SO, Mn is limitin reagent

(b)

According to first law of Faraday's electrolysis,

W = M c t / Z F

t = W Z F / M c

t = 26.9 * 2 * 96500 / (55 * 0.0552)

t = 171005 s

t = 2850 min

t = 47.5 h

(c)

1 mol of Mn dissolved = 1 mol Co deosited

so, 0.489 mol of Mn dissolved = 0.489 mol Co deposited

So, mass of Co deposited = 0.489 * 58.9 = 28.8 g.

(d) Remaining moles of Co2+ in the solution after completion of reaction = 0.616 - 0.489 = 0.127 mol

therefore,

[Co2+] = 0.127 * 1000 / 616 = 0.206 M

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