Electrochemical Cells

A series of free IGCSE Chemistry Activities and Experiments (Cambridge IGCSE Chemistry).

Cells and Batteries

• If we take two different metals and place them into an electrolyte then we produce electricity.
• An electrolyte is simply a solution that can conduct electricity, for example a solution of an ionic compound.
• A cell can only produce electricity for a certain period of time. Eventually, the chemicals in the cell run out and the reaction stops.
• Cells only produce electricity if we use metals with different reactivities.
• The greater the difference between the reactivity of the metals, the greater the potential difference produced by the cell.
• The electrolyte also affects the potential difference.
• A battery contains two or more cells connected in series to produce a greater voltage.
  

Voltaic Cells with a salt bridge
A cell uses a chemical reaction to create electricity. Moving electrons create electricity, and electrons flow from the anode (the site of oxidation), to the cathode (the site of reduction).
In order for a cell to generate electricity for a longer time, it may be separated into two half-cells connected by a salt bridge. The salt bridge helps to balance charge, and lets ions move between the two half cells.
We can write redox half reactions for the two half cells, which show the gain and loss of electrons.

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Voltaic Cell Experiment
Metal strips dipped in solutions of appropriate metal salts are linked with a salt bridge.

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Questions

1. What was the voltage when we used zinc and copper as the electrodes?
2. Would you expect the voltage to increase or decrease if you replace the zinc electrode with an iron electrode? Why?
3. Heat energy given out follows a similar trend when measured in relation to copper. Compare the heat energy released for zinc and copper electrodes to the energy released for iron and copper electrodes.

Answers

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  1. About 0.75 volts.
  2. The voltage will decrease because iron is less reactive (less standard reduction potential) than zinc.
  3. The heat energy released for zinc and copper electrodes would be more than the energy released for iron and copper electrodes.

Six-Way Cell
How to build micro-voltaic cells using metals and metal ion solutions on filter paper?
Measure the voltages and compare the standard reduction potential for each metal.

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