Electrochemical cells

Electrochemical cells Two types of electrochemical cells: voltaic (galvanic) cells and electrolytic cells. Voltaic cell – a cell that generates electricity from a spontaneous chemical reaction. Electrolytic cell – a cell that uses electricity to drive a chemical reaction

Electrochemical cells If we place a strip of zinc metal in a solution of copper ions (CuSO4), the copper is reduced and precipitates out of the solution.

voltaic Cells However, if we separate the two reactions into half-cells, and connect the two half-cells, then the electrons will travel through an external circuit from one half-cell to the other, producing an electric current. The electrons will travel from the anode, which in a voltaic is the negative electrode, to the cathode, which in a voltaic cell is the positive electrode.

Voltaic cells Electrodes are the surfaces upon which oxidation and reduction occur. The anode is the electrode on which oxidation occurs and the cathode is the electrode on which reduction occurs. (RED CAT) Electrons always travel from anode to cathode.

Voltaic Cells To build a voltaic cell: 1. Make two half cells. Each half cell is prepared by placing a strip of metal into a solution of its ions. The metal strips act as the electrodes.

Voltaic cells 2. Connect the two electrodes with a wire and attach a voltmeter to measure the voltage of the cell.

Voltaic cells Copper has less of a tendency to lose electrons than zinc. Consequently, there are fewer electrons on the copper metal strip, which means that it will have a more positive potential than the zinc strip.

Voltaic cell Connect the two half cells with a salt bridge to complete the circuit. The salt bridge is a glass tube or strip of absorptive paper that contains an aqueous solution of ions. Movement of these ions neutralizes any build-up of charge and maintains the potential difference. Anions move in the salt bridge from the cathode to the anode. Cations move in the salt bridge from the anode to the cathode. The solution chosen is often aqueous NaNO3 or KNO3, as these ions will not interfere with the reactions at the electrodes. Without a salt bridge, no voltage is generated.

Voltaic cells

Cell diagram convention An abbreviated version of a voltaic cell

Cell diagram convention

Voltaic cells Electrons flow through the external circuit because there is a potential difference between the two half cells. The anode is more negative and the cathode is more positive. Different combinations of metals can produce voltaic cells with different voltages. the voltage generated will be determined by the difference in reducing strength of the two metals. For example, if the copper half cell is changed to a silver half cell, a larger voltage would be produced because the difference in electrode potentials of zinc and silver is greater than between that of zinc and copper. Electrons will flow from anode to cathode (zinc to silver)

Voltaic cells

Voltaic cells