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Module 1: Practical chemistry for exams›PAG 8.2 - Electrochemical cells 2

PAG 8.2 - Electrochemical cells 2

An overview of PAG 8.2 - Electrochemical cells 2

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In OCR Chemistry Required Practical 8 (PAG 8.2 ), a series of standard half-cells are produced from metals and solutions of their ions. EMF values are obtained for different combinations of half-cells.

Half-cells to be tested are:

In OCR PAG 8.2: Electrochemical cells 2, there are several important safety requirements to be aware of (beyond normal lab practice such as wearing goggles).

Dispose of chemicals as directed by your teacher

Experimental method for OCR Chemistry Required Practical 8 (PAG 8.2)

EXPERIMENTAL METHOD OCR PAG 8.2 1 Prepare metal/metal-ion half-cells for Cu, Fe(II), Zn, and Mg. Pour 50 cm3 of 1.0 mol dm-3 solutions of metal ions into 100 cm3 beakers. Clean a metal strip with a piece of emery paper until the metal surface is shiny and corrosion-free. Dip the strip of cleaned metal into the appropriate metal ion solution. Clip the metal strip to the side of the beaker with a crocodile clip and wire. 2 Prepare a salt bridge. Take a large filter paper or chromatography paper and fold it up into a long strip. Submerge the filter paper strip in saturated potassium nitrate(V) solution. Squeeze out excess solution. 3 Connect a pair of beakers to make an electrochemical cell. Place two beakers side by side. Connect the crocodile clips and wires to a voltmeter. Carefully place the salt bridge over both beakers and ensure it dips into both electrolyte solutions but does not touch the metal strips. Switch the connections if needed to get a positive EMF. Record the voltage and the electrode connected to the positive terminal. 4 Repeat for a variety of half-cell combinations. Discard the salt bridge and make a fresh one for each measurement. Cell + electrode EMF (volt) Cu + Zn Cu + Mg Cu + Fe Cu + Mg Zn + Fe Mg + Fe

To ensure clean and reactive metal surfaces when preparing an electrode for accurate voltage readings.

A vertical rectangular shape with a gradient fill transitioning from a darker orange at the top to a lighter orange at the bottom, outlined in black.

Do

Clean all metal surfaces thoroughly with emery paper and degrease with propanone to remove oxide layers and grease.

A rectangular shape with a smooth, gradient orange surface, resembling a piece of caramel or toffee.

Don't

Skip the cleaning or degreasing step – this increases surface resistance and affects the EMF value.

It is important to have strong connections between half cells.

An illustration showing two beakers connected by a tube. The left beaker contains a copper electrode labeled 'Cu' and a solution labeled 'Cu2+ (aq)', while the right beaker contains a zinc electrode labeled 'Zn' and a solution labeled 'Zn2+ (aq)'. A voltmeter is connected to both electrodes.

Do

Ensure firm connections between metal electrodes and the voltmeter using crocodile clips, checking for a stable reading.

An illustration showing a setup with two beakers containing Cu2+ (aq) and Zn2+ (aq) solutions. A copper rod labeled 'Cu' is immersed in the left beaker, while a zinc rod labeled 'Zn' is in the right beaker. A voltmeter is connected to both rods with alligator clips.

Don't

Allow loose or corroded connections – these can cause unstable or fluctuating voltage readings.

Calculate the standard cell potential by using:

With , rearrange to calculate the experimental electrode potentials of , and , then compare with standard values.