Experiment 4: Constructing an iron/ copper cell

· An iron/ copper cell was set up by connecting the same Fe/ Fe²⁺ and Cu/Cu²⁺ half-cells that was used in the previous two experiments.

· Again, a fresh salt bridge was used.

· The E⁰_cell was recorded.

Experiment 5: Effect of concentration on E⁰_cell

· Le Chatelier’s principle was used to predict the changes that occur if the ion concentration in each equilibrium system is reduced.

· What will be the effect of decreasing the concentration of the copper ions on the tendency for the copper electrode to accept electrons from the zinc?

· What will be the effect on E⁰_cell of decreasing the concentration of copper ions?

- A Zn/Cu cell was set up similar to that of experiment 2 but featuring 0.001 M Cu²⁺ instead of 1 M Cu^2+.

· E⁰_cell was also measured with the following concentrations of Cu²⁺ :

- 0.01 M

- 0.1 M

- 1 M (this is a re-measurement)

· A fresh salt bridge was used each time (at the low concentrations, it is very important to pay careful attention to possible contamination in the copper half=cells as small quantities of impurities would give rise to large errors).

· A graph of E⁰_cell versus log [Cu²⁺] was plotted featuring four data points.

 

IV. Results

Experiment 1: Reaction between Zn and Cu²⁺

Zn_(s) +Cu²⁺ _(aq) → Cu⁰ _(s) ↓ + Zn²⁺ _(aq)

Observations: Solid, Zn, replaced Cu (II). Copper became precipitate, and the test tube became darker. Zn is oxidized, while the copper is reduced. This is exothermic reaction.