An experiment measuring the potential difference generated by various simple electrochemical cells.

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8/1/04

Emma Duckworth 7E

An experiment measuring the potential difference generated by various simple electrochemical cells.

Aim:

The purpose of this experiment was to correctly construct three simple electrochemical cells and then measure the potential difference, including the polarity, between the two metal electrodes in each cell.

Apparatus:

==> Chemicals/ substances:

* Copper sulphate solution (1M)

* Strip of copper foil

* Zinc sulphate solution (1M)

* Strip of zinc foil

* Silver nitrate solution (1M)

* Silver wire

* Saturated potassium nitrate solution

==> Additional apparatus:

* Safety goggles

* Emery paper

* 4 beakers

* 3 connecting leads with crocodile clips

* Filter paper

* High resistance voltmeter

Diagram:

Method:

==> Clean each metal strip with separate pieces of emery paper (if necessary).

==> Construct the three listed electrochemical cells by the following method:

Cell

Half- cells

(1)

Zn2+ (aq) + 2e- ? Zn (s)

Cu2+ (aq) + 2e- ? Cu(s)

(2)

Ag+ (aq) +e- ? Ag(s)

Cu2+ (aq) + 2e- ? Cu(s)

(3)

Ag+ (aq) +e- ? Ag(s)

Zn2+ (aq) + 2e- ? Zn (s)

==> Place each of the two metal strips required for the cell in a separate beaker. Hold each strip against the inside of the beaker so that it comes over around 2 cm above the rim and fold this projection down over the rim of the beaker, clamping it into position with a crocodile clip attached to a lead.

==> Pour about 20 cm3 of the appropriate salt solution so each metal strip is immersed in a solution of its ions (for example zinc sulphate in the beaker with the zinc metal in).

==> Make a salt bridge by immersing a strip of filter paper in saturated potassium nitrate solution and let the excess solution drain off it before using it.

==> Connect the electrodes to a high resistance voltmeter and complete the circuit with the salt bridge. (See diagram). Make sure the 2 electrodes are connected to the correct terminal of the voltmeter - the more reactive/ better reducing agent at the negative terminal (on the left) and the less reactive/ better oxidising agent at the positive terminal (on the right). If the reading is negative, change the electrodes around so the reading is positive.

==> Record the potential difference shown on the voltmeter, including the sign of polarity and note which electrode was positive and which was negative.

==> Remove the salt bridge as soon as possible and dispose of it. Disconnect the voltmeter.

==> Repeat these steps for the other 2 cells.

Results:

Cell

Positive electrode

Negative electrode

Potential difference
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(1)

Cu2+ (aq) + 2e- ? Cu(s)

Zn2+ (aq) + 2e- ? Zn (s)

+ 1.06 V

(2)

Ag+ (aq) +e- ? Ag(s)

Cu2+ (aq) + 2e- ? Cu(s)

+ 0.38 V

(3)

Ag+ (aq) +e- ? Ag(s)

Zn2+ (aq) + 2e- ? Zn (s)

+ 1.35 V

Questions:

(1) Considering cell (1)

(a) To make the zinc electrode negative, an oxidation reaction is occurring, whereby the zinc is being oxidised and releasing electrons. The zinc is a more reactive metal than copper, meaning ...

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