The Daniell cell was invented by John Daniell in 1836.

One half-cell comprises a zinc strip dipped into a solution containing zinc ions.

The other half-cell comprises a copper strip dipped into a solution containing copper ions. The two metal strips are connected together via a voltmeter.

A salt bridge containing saturated potassium nitrate(V) solution completes the circuit.

We can use standard electrode potentials to calculate the potential difference, E ө, of the cell. cell

E ө can be calculated using this equation. cell

First, substitute the electrode potential for the copper half-cell.

Next, substitute the electrode potential for the zinc half-cell.

The potential difference of the Daniell cell is V.

We can use electrode potentials to predict which reactions can happen. One way to do this involves drawing two vertical lines to represent the two electrodes.

Draw a curly line at the bottom to help us later to decide the direction of electron movement.

We will label each vertical line with a reaction taken from a table of standard electrode potentials. We will put the reaction with the highest E ө value on the right.

What reaction happens if two half-cells, Ag + /Ag and Cu 2+ /Cu, are connected together?

The E ө value for Cu 2+ /Cu is lower than the E ө value for Ag + /Ag, so we put copper on the left and silver on the right.

Draw an arrow to show the direction of electron flow. It will always be from left to right in these diagrams.

We can calculate the potential difference for the spontaneous cell reaction.

It is equal to the most positive potential minus the least positive potential.

The potential difference for this cell is V.

Electrons flow towards the silver half-cell. This means that the reaction taking place there will be Ag + + e – → Ag.

Electrons flow from the copper half-cell, so the reaction taking place there will be Cu → Cu e –.

Reduction takes place on the right, which is the positive terminal of the cell.

Oxidation takes place on the left, which is the negative terminal of the cell. Adding the two half-reactions, we find that the overall cell reaction is Cu + 2Ag + → Cu Ag.