SIMPLE ELECTROLYTIC CELL AND SYNTHESIS OF WATER

A simple electrolytic cell Students pouring chemicals in the cell

Outline of the experiment We can make simple electrolytic cells applying locally available materials such as water bottles, rubber sandals and straws. After filling the cell with diluted sodium hydroxide aqueous, direct electric current which is passing through the anode to cathode can break down water to hydrogen gas and oxygen gas. Set up the water synthesis chamber on top of a bucket which is filled with water. Immerse the electrolytic cell in the water of the bucket, and then collect the hydrogen and oxygen gas into the chamber. Using a gas igniter (piezoelectric igniter) which is connected to the chamber we can start the synthesis of water. If the set up is perfect you can see orange flame and hear big explosive sound. Students must do this experiment under teacher's tutelage.

Materials and tools 1. Electrolysis and how to make simple electrolytic cell Parts of simple electrolytic cell Two 500ml Voltic bottles and caps, five 18mm diameter rubber cork made of a rubber sandal, a ball point pen tube, a 5mm diameter flexible straw, two carbon rods removed from two D size manganese dry cells, and a container to catch drain (overflow). Tools to make an electrolytic cell A 14mm diameter glass test tube, a test tube holder, a Bunsen burner or gas stove, a cork borer set, some drill bits and a drill, and a small saw. Electrolysis of water (sodium hydroxide aqueous) 12V DC supplier (eight D size cells connected in series or a motor cycle battery or a reliable AC-DC converter)、two electric wires with worm clips, a 10ml or 25ml measuring cylinder, a funnel, 1000ml of 1mol/litre sodium hydroxide aqueous, and a DC ammeter. 2. Synthesis of water 500ml plastic bottle, a bottle cap whose bottom is removed, a 23mm diameter rubber cork, two paper clips, two electric wires with worm clips, a gas igniter (piezoelectric igniter), a A4 laminate sheet, a cutter, a transparent plastic bucket, water (at least 20litres), a pair of pliers, tissue paper, and protective goggles.

Method 1. How to assemble the electrolytic cell Make holes on 500ml Voltic bottles like figure 1 and 2 using the following method. Hold a 14mm diameter glass test tube with a test tube holder. Heat the bottom of the tube with flame of Bunsen burner then remove the tube from the flame and put the bottom of the tube on the bottle to melt the plastic making a circular shape. The holes will have approximately 16mm diameters. Seal the holes with 18mm diameter rubber corks which are made of a rubber sandal. We must make proper holes on the cork using a drill and drill bits as follows. Connect the chambers with a ball point pen tube which is cut properly by a saw. Use carbon rods taken from D size manganese dry cells for anode and cathode. (File or sandpaper the carbon rods before insertion.) We can use a 5mm diameter flexible straw as an overflow tube. Do not disassemble alkaline cells! Use manganese dry cells! After finishing the assembly, please check out leakages of water. 2. Electrolysis of water Remove both caps of the electrolytic cell and pour 1mol/litre of sodium hydroxide aqueous (dissolve 40g NaOH into water and make 1000ml solution) gently using a funnel. Cap the lid slowly to avoid entry of air bubbles. Lead the overflow tube on a drain container. Connect 12V DC power to the cell. Keep on doing electrolysis until we can collect 12ml of overflow which is equivalent to 8ml of hydrogen gas and 4ml of oxygen gas.

For the safe water synthesis experiment we must not collect big amount of hydrogen and oxygen gas!

3. How to make the water synthesis chamber

Make an electric discharger using two paper clips, 23mm diameter rubber cork, cutter and a pair of pliers (Figure 3). Connect a gas igniter to the upper terminals with wires and then confirm if you can see discharges in the lower gap of the clip wires. Insert the discharger into an upper part of 500ml drink plastic bottle (Figure 4). Pass through a pair of laminate sheets in a laminator and make a chamber holder like figure 5. Make a hole on it and fix the chamber. Pour water into the bucket up to near the rim (leave space for about 1.5litre of water). Immerse the chamber into the bucket and fill the chamber with water. Immerse the electrolytic cell in the water and collect hydrogen and oxygen gas in the chamber.

4. Ignition and synthesis of water

Remove water from the top of the chamber using tissue paper. Connect the gas igniter and the chamber terminals with wires like figure 8. Make sure there is nobody near the chamber except a student who ignites. He or she must wear protective goggles and observers must stand at least 2m away from the chamber. Make sure there is no electric bulb or tube on the ceiling above the chamber. The student who is in charge of the ignition must stretch his or her arm as much as possible then start countdown. At “zero” the student can ignite. If nothing happens, remove one of the wires and then the teacher can start checking the electric leak and connections of the set up.

Ignited H2 and O2 mixture 1/30 second later

Caution After you immerse the electrolytic cell in the bucket, there is some sodium hydroxide in the water. If you feel something unusual on your skin, wash it immediately with running water. Common drink bottles are made from polyethylene terephthalate (PET). Since PET is ester of terephthalic acid and ethylene glycol, it is hydrolyzed by sodium hydroxide. If you repeat this experiment several times, you may find leakages from the container. Please change the bottles to new ones when you find a leakage.