Question

Use the Nernst equation to calculate the expected voltage of the concentration cell before the addition of the 10 extra drops of 0.10 M copper(II) nitrate solution. Use your experimental temperature. How did the addition of 10 drops of 0.10 M cupric nitrate affect the concentration cells voltage? Why?

Temp. 21C

E=91V

10 drops 75.8V

Answer 1

The addition of 10 drops of 0.10 M cupric nitrate does not affect the concentration cell's voltage.

Explanation: For a concentration cell, E^o_cell = 0

According to Nernst equation:

E_cell = E^o_cell - 0.05916 V/2 Log{[Cu²⁺]_{anodic half-cell}/[Cu²⁺]_{cathodic half-cell}}

i.e. E_cell =0 - 0.05916 V/2 Log{[Cu²⁺]_{anodic half-cell}/[Cu²⁺]_{cathodic half-cell}}

i.e. E_cell = 0.02958 V Log{[Cu²⁺]_{cathodic half-cell}/[Cu²⁺]_{anodic half-cell}}

The addition of 10 drops of 0.10 M cupric nitrate doesn't affect the ratio [Cu²⁺]_{cathodic half-cell}/[Cu²⁺]_{anodic half-cell}, hence the cell potenital (E_cell) remains constant as before the addition of 10 drops of 0.10 M cupric nitrate