# Lesson 9 - Lab work

Introduction lab work

You have been given a home-made electrochemical cell (schematically shown in figure 37), that functions both as electrolyser and fuel cell. The protruding bolts serve as contact points for the energy supply and/or the multi meter. The electrolyte (the electrically conductive fluid) can be placed in between the separate transparent cover and the fixed transparent plate that is glued to the bottom plate. Because we want to do a number of quantitative measurements, you will not use a photovoltaic cell to power the electrolyser, but an adjustable power supply.

Materials

- Home-made electrochemical cell
- Adjustable power supply
- Multi-meter
- 4 measuring cables
- 2 alligator clips
- Stopwatch/timer
- 1,0 M NaCl-solution
- Dropper
- Wash bottle of demineralised water
- Universal pH-paper

Part A – Electrolysis 1,0M NaCl-solution

In this part of the lab work you will electrolyse water using a NaCl-solution as an electrolyte. The gasses that are produced can then be used to produce electrical energy using the same device. That will be done in part B of the lab work.

Part B – Determining the produced voltage

Before electrolysis the voltage over the device was 0 V. After electrolysis a non-zero voltage could be measured. We could thus say that the device was charged or fuelled during electrolysis. We could now use the device to supply a calculator with electrical energy for example.

In an electrochemical cell and with electrolysis graphite (carbon) electrodes are often used. The price of graphite is less than € 2 per kg. Platinum costs about € 40,000 per kg. However, we still use platinum wire to serve as electrodes in this device.

In part B you measured the open voltage which means that there was no current during the measurement. As there was no current there was no flow of electrons and there were no half reactions. Despite of that, the voltage dropped during the measurement.