Practical Techniques - Electrochemistry (SQA National 5 Chemistry): Revision Note

Testing electrical conductivity

• This experiment is used to determine whether a substance can conduct electricity

• For a substance to conduct, it must contain charged particles that are free to move

Apparatus

• A low-voltage power supply or battery

• Two inert (unreactive) electrodes, usually made of graphite (carbon)

• A beaker to hold the substance being tested

• A lightbulb or ammeter to detect if a current is flowing

Method

1. Set up the circuit as shown, with the electrodes placed in an empty beaker

2. Test the substance as a solid

   • Add the solid to the beaker, ensuring it touches both electrodes

   • Observe if the bulb lights up

3. Test the substance as a liquid

   • If the substance is soluble, add water to create a solution

   • Observe if the bulb lights up

   • If the substance is insoluble, safely heat it until it becomes molten

   • Observe if the bulb lights up

Expected results

• The conductivity of a substance depends on its bonding and structure

• The results you would expect for the main substance types are summarised below:

Setting up electrochemical cells

• An electrochemical cell (or battery) uses a chemical reaction to produce a voltage

• The most common setup involves two separate half-cells connected together

Apparatus

• Two beakers

• Two different metal electrodes

• Solutions of the corresponding metal ions

• A voltmeter

• Wires and crocodile clips

• An ion bridge (filter paper soaked in an electrolyte like potassium nitrate)

Method

1. Create half-cell 1:

   • Place a metal rod into a beaker containing a solution of its own ions

     • For example, place a zinc rod into a beaker of zinc sulfate solution

2. Create half-cell 2:

   • Do the same for a different metal

     • For example, place a copper rod into a beaker of copper(II) sulfate solution

3. Connect the electrodes:

   • Use crocodile clips and wires to connect the two metal rods (the electrodes) to a voltmeter

4. Complete the circuit:

   • Soak a strip of filter paper in a neutral ionic solution (like potassium nitrate) and use it to connect the two beakers

     • This is the ion bridge

5. Observe the voltage produced on the voltmeter

Practical tip

• If one of the half-cells does not contain a metal (for example, an iodine/iodide solution), a graphite (carbon) rod should be used as the inert electrode in that half-cell

Solution electrolysis

• Electrolysis is the process of using electricity to break down an ionic compound

Apparatus

• A beaker to hold the electrolyte

• An ionic solution (the electrolyte)

• Two inert graphite electrodes

• A DC (direct current) power supply

• Wires and crocodile clips

Method

1. Prepare the electrolyte

   • Pour the ionic solution to be tested (the electrolyte, e.g., copper(II) chloride solution) into a beaker

2. Set up the electrodes

   • Place two inert graphite electrodes into the solution, making sure they do not touch

3. Connect the power supply

   • Use wires to connect the electrodes to a DC (direct current) power supply

   • It is crucial to use a DC supply so the electrodes are fixed as positive and negative

4. Switch on the power supply

5. Observe the chemical changes that occur at each electrode

   • For example, bubbles of gas, solid forming