A voltaic cell consists of a Zn/Zn2+ half-cell and a Ni/Ni2+ half-cell at 25 C.

Question

A voltaic cell consists of a Zn/Zn2+ half-cell and a Ni/Ni2+ half-cell at 25 C. The initial concentrations of Ni2+ and Zn2+ are 1.30molL1 and 0.130 molL1, respectively.

Zn2+(aq)+2eZn(s)E=0.76V
Ni2+(aq)+2eNi(s)E=0.23V

1. What is the initial cell potential? Express your answer to two decimal places and include the appropriate units.

2. What is the cell potential when the concentration of Ni2+ has fallen to 0.600 molL1? Express your answer to two decimal places and include the appropriate units.

3. What are the concentrations of Ni2+ and Zn2+ when the cell potential falls to 0.45 V?

Explanation / Answer

1. The more reduction potential electrode acts as a cathode.

Ni/Ni+2 act as a cathode and Zn/Zn+2 as anode.

Con of Ni+2 = 1.3M, Con of Zn+2 = 0.130M.

Overall cell reaction:       Ni+2 + Zn ® Zn+2 + Ni

E0Zn+2/Zn= -0.76V

  E0Ni+2/Ni = -0.23V

    E0 = 0.53V

Nernst Equation: E = E0 – (0.059/n) log(Zn+2/Ni+2)

E = 0.53 – (0.059/2) log(0.13/1.3)

E = 0.56V

2. If con of Ni+2 is 0.6M

E = 0.55V

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