The Volta cell
To introduce another method of producing a difference of potential between two electrodes, measuring the voltage of a single Volta cell and then of two Volta cells linked in series.
Cosa imparano gli studenti
La scienza alla base di questo esperimento
Alessandro Volta in 1799 described a galvanic cell for the first time. The difference between the Volta cell and the Daniell cell is that, although both are copper and zinc cells, in the Volta cell the solutions in both half cells are dilute sulphuric acid.
Zinc reacts with diluted sulphuric acid giving zinc sulphate and hydrogen. The oxidation of zinc, which dissolves and produces ions, allows the reduction of hydrogen ions to molecular hydrogen according to the following equations.
Connecting the electrodes by means of a wire allows electrons to flow from zinc to copper. When the electrons reach the surface of the copper, they reduce the hydrogen ions, producing bubbles on the copper electrode. The development of a film of molecular hydrogen over the surface of the electrodes causes a decrease of the voltage in the voltaic cell and so screens it from the hydrogen ions in the solution.
Attrezzatura utilizzata
- Digital multimeter — 2275.10
- 1 × Connecting wire, red — 2522.03-04
- 2 × Connecting wires, black — 2522.04-08
- 4 × Crocodile clips — 2531.52
- 2 × Copper electrodes — 4716.21
- 2 × Zinc electrodes — 4716.16
- 2 × Test cell covers — 4718.10
Sostanze chimiche e reagenti
- Sulphuric acid 0.5 M — R:35 S:26-30-45
Note sulla sicurezza
Domande per gli studenti
- Record the measured voltages for a single cell, two cells in series, and in parallel.
- Where is there an evolution of gas? What gas is it?
- What happens on shorting the cells? Why?
Cosa aspettarsi
<p>For a single cell and for two cells in parallel the voltage is about 1.05 V, but it quickly declines to about 0.90 to 0.95 V. The voltage measured for a series (about 1.8 V) is the sum of the voltages of each cell.</p><p>On the zinc electrode hydrogen ions are reduced to hydrogen. During the observation the zinc electrode produces bubbles.</p><p>Also in this second experiment the zinc electrode produces bubbles of hydrogen.</p><p>After this operation bubbles appear not only on the zinc but also on the copper electrodes. Electrons flow to copper electrodes and hydrogen ions are reduced also at this electrode.</p><p>The presence in the circuit of a measuring instrument (voltmeter) with a high resistance hinders the passage of electrons, so that the reduction of hydrogen ions occurs almost entirely on the zinc electrode, since the amount of electrons that reach the copper electrode is very small.</p>
Smaltimento
Dispose of the solution into the waste container.
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