The Electrolysis of WaterThe Electrolysis of WaterTwo pencils act as the electrodes in this petri dish containing a solution of sodium sulfate and universal pH indicator. Over a period of several minutes, tiny bubbles of gas form on the electrodes. At the negative electrode the indicator turns puple. Near the positive electrode the indicator turns yellow.
A different apparatus with higher current densities is neeed if we want to collect and identify the gases. To accurately measure the amount of gases produced, we use sulfuric acid as the electrolyte. The rate of gas formation is obviously much lower at the positive anode than at the negative cathode. At a current of 50 milliamps, we collect gas for about an hour. On the right almost twice as much gas forms at the negative electrode.
Standard flame test identify the two gases. The gas produced at the positive electrode ignites a glowing splint. The other gas burns with a slight pop.