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Module 1: Practical chemistry for exams›PAG 8.1 - Electrochemical cells 1

PAG 8.1 - Electrochemical cells 1

An overview of PAG 8.1 - Electrochemical cells 1

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In OCR Chemistry Required Practical 8 (PAG 8.1 ), the effect of concentration changes on the value of the EMF of a copper and iron cell is investigated.

Five different ratios of iron ions are used in the experiment.

A table displaying mixtures and their corresponding ratios of Fe2+ to Fe3+. The table includes the following entries: Mixture A with a ratio of 1 : 5, Mixture B with a ratio of 1 : 3, Mixture C with a ratio of 1 : 1, Mixture D with a ratio of 3 : 1, and Mixture E with a ratio of 5 : 1.

In OCR PAG 8.1: Electrochemical cells 1, 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 8.1)

EXPERIMENTAL METHOD OCR PAG 8.1 1 Prepare the standard copper half-cell. Clean a copper metal strip with emery paper until the metal surface is shiny and corrosion free. Add 50 cm3 of 0.1 mol dm-3 solution of copper sulfate solution to a 100 cm3 beaker. Clip the metal strip to the side of the beaker with a crocodile clip and wire. Connect the copper cell to a terminal on the voltmeter. 2 Prepare the iron half-cell. Measure out 50 cm3 of a mixture into a 100 cm3 beaker. Clip a graphite electrode with a crocodile clip to the inside of the beaker. Connect the electrode to the other terminal of the voltmeter. 3 Prepare the 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. 4 Measure and record the EMF. Take the reading from the voltmeter and record it in the results table. 5 Repeat for all test solutions. Experiments can be completed using the same copper cell, but a fresh salt bridge should be made each time. Mixture Ratio Fe2+: Fe3+ EMF/V A 1:5 0.57 B 1:3 C 1:1 D 3:1 E 5:1

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.

Use the voltage results to identify the electrode reactions:

and giving

Compare the voltages for the different ratios.

As decreases, the electrode potential becomes less positive and decreases.