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

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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