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9 May, 06:05

Calculate the time required for a constant current of 0.800 A to deposit 0.250 g of

(a) Co (II) as the element on a cathode and

(b) as Co3O4 on an anode. Assume 100% current efficiency for both cases.

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Answers (1)
  1. 9 May, 06:17
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    a) 17 min

    b) 4.2 min

    Explanation:

    The time required can be calculated by:

    t = q/i

    Where q is the charge, and i is the current. The charge may be calculated by:

    q = na*n*F

    Where na is the number of moles of the anality, n is the number of moles of electrons, and F is the faraday constant (96485 C/mol).

    a) The element will be in the cathode, thus it will reduce:

    Co⁺² + 2e⁻ ⇄ Co

    The molar mass of Co is 58.93 g/mol, thus:

    na = mass/molar mass

    na = 0.250/58.93

    na = 4.24x10⁻³ mol

    n = 2 mol

    q = 4.24x10⁻³*2*96485

    q = 818.2 C

    t = q/i

    t = 818.2/0.8

    t = 1022.74 s/60

    t = 17 min

    b) In the anode an oxidation is happening, and n = 2 too. The molar mas of Co3O4 is 240.8 g/mol, thus:

    na = 0.250/240.8

    na = 1.04x10⁻³ mol

    q = 1.04x10⁻³*2*96485

    q = 200.3 C

    t = 200.3/0.800

    t = 250.43 min/60

    t = 4.2 min
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