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18 March, 16:49

Given that E°red = - 1.66 V for Al3+ / Al at 25°C, find E° and E for the concentration cell expressed using shorthand notation below.

Al (s) Al3 + (1.0 * 10-5 M) Al3 + (0.100 M) Al (s)

A) E° = 0.00 V and E = + 0.24 V

B) E° = 0.00 V and E = + 0.12 V

C) E° = - 1.66 V and E = - 1.42 V

D) E° = - 1.66 V and E = - 1.54 V

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  1. 18 March, 17:40
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    E° = 0.00 V

    E = 0.079 V

    Explanation:

    We can identify both half-reactions occurring in a concentration cell.

    Anode (oxidation) : Al (s) → Al³⁺ (1.0 * 10⁻⁵ M) + 3 e⁻ E°red = - 1.66 V

    Cathode (reduction) : Al³⁺ (0.100 M) + 3 e⁻ → Al (s) E°red = - 1.66 V

    The global reaction is:

    Al (s) + Al³⁺ (0.100 M) → Al³⁺ (1.0 * 10⁻⁵ M) + Al (s)

    The standard cell potential (E°) is the difference between the standard reduction potential of the cathode and the standard reduction potential of the anode.

    E° = E°red, cat - E°red, an = - 1.66 V - (-1.66 V) = 0.00 V

    To calculate the cell potential (E) we have to use the Nernst equation.

    E = E° - (0.05916/n). log Q

    where,

    n: moles of electrons transferred

    Q: reaction quotient

    E = 0.00 V - (0.05916/3). log (1.0 * 10⁻⁵/0.100)

    E = 0.079 V
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