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9 May, 12:32

When zinc is refined by electrolysis, the desired half-reaction at the cathode is A competing reaction, which lowers the yield, is the formation of hydrogen gas: If 85.6% of the current flowing results in zinc being deposited, while (100-85.6) % produces hydrogen gas, how many liters of H2, measured at STP (hydrogen gas occupies 22.4 L/mol), form per kilogram of zinc

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  1. 9 May, 15:32
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    volume of hydrogen = 57.6 L

    Explanation:

    Desired Half Reaction: Zn²⁺ (ag) + 2e⁻ → Zn (s)

    Competing Reaction = 2H⁻ (ag) + 2e⁻ → H₂ (g)

    Desired Half Reaction: Zn²⁺ (ag) + 2e⁻ → Zn (s)

    2 moles of electrons are transfer to deposit 1 mole of zinc (65.41g).

    The number of moles transferred to deposit 1kg will be

    1000/65.41 * 2 = 30.6 mol

    converting to columb,

    1 mole = 96485C

    therefore, 30.6mol = 96485 * 30.6

    =2.95*10^6 C

    For 85.6% of current flowing, the total current flowing is calculated as

    85.6% * x = 2.95*10^6

    x = 2.95*10^6/0.856

    x = 3.446 * 10^6 C

    Calculating the quantity utilized in producing hydrogen gas, we have

    = (100 - 85.6) % * 3.446 * 10^6

    =14.4% * 3.446 * 10^6

    =496224C

    Competing Reaction = 2H⁻ (ag) + 2e⁻ → H₂ (g)

    Calculating the number of mole transferred to the charge, we have

    496224 / 96485 = 5.14 mol

    volume of hydrogen = 5.14 * 22.4/2

    = 57.6L
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