Lesson 2 - Page 1




1. Students will learn about electrolysis.
2. Student will make hydrogen and oxygen.


Water is a stable compound, whose elemental make-up confused chemists for centuries. They did not think water could be broken down into simple substances. Water was recognized as a compound of hydrogen and oxygen in the eighteenth century. It was identified as the product of combustion between oxygen and hydrogen gases.

To split water into its components requires energy. Electrolysis, or the process that allows electrical energy to bring about a chemical change, will be used in this experiment to separate water into hydrogen gas and oxygen gas. There are many applications of electrolysis especially in the manufacture of sodium, hydrogen, oxygen, fluorine, aluminum, and chlorine.


carbon rods, 6 volt battery, 15 250 mL beakers, 30 10 mL graduated cylinders, matches


Connect one end of each of the two wires to a carbon rod. The carbon rods are easily damaged and broken so care must be used. Connect the remaining ends of the two wires to the connectors on the 6 volt battery. Add 200 mL of water to a 250 mL beaker. To this solution add about 1 tablespoon of epsom salt. Fill each of the two 10 mL graduated cylinders with some of the water and epsom salt solution. Immerse the carbon rods into the graduated cylinders. Quickly flip the graduated cylinders over and place them in the beaker. The majority of the carbon rod should be inside the graduated cylinder. There should also be enough water in the graduated cylinder so that the carbon rods are completely immersed.

Once the graduated cylinders are both placed in the beaker bubbles will start to form on the carbon rods. The formation of the bubbles indicates the evolution of hydrogen and oxygen gas. Because water is composed of 2 parts hydrogen to one part oxygen, the carbon rod evolving hydrogen gas will show twice as much activity as the rod evolving oxygen. This can be verified using the graduated cylinder provided that not much water has been lost during initial transfer into the beaker. The graduated cylinders will capture the gases and the displacement of water can be measured on the graduated cylinder.

To stop the experiment simply disconnect the battery. The presence of hydrogen gas can be verified using a lit wooden stick. Since hydrogen is explosive, exposing a small volume to a flame will result in a "pop." To check for oxygen use a glowing wooden splint (flame has been blown out) and place it in the test tube with oxygen. The flame will emerge in oxygen.




[ Chemical Interactions]  [ Physical Science]