Lesson 4 - Page 3


Electroplating a key with copper

Electrolysis of pure or distilled water is very slow.  You can speed it up by adding an electrolyte such as an acid or base.  Salts like epsom salt, works very well. 

The overall reaction is  2H2O(liquid) → 2H2(gas) + O2(gas)

Electrolysis is important in other applications especially in the manufacture of sodium, hydrogen, oxygen, fluorine, aluminum, and chlorine.  Electroplating which is used to put a thin layer of certain metals on other metals is a direct application from the invention of electrolysis.

Now, let’s make some hydrogen and oxygen from water.

Electrolysis set-up

Connect one end of each of the two alligator clips 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 test tubes or 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 generation of hydrogen and oxygen gas. Because water is composed of 2 parts hydrogen to one part oxygen, the carbon rod creating 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 using 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."  Be careful and listen to all instructions. To check for oxygen use a glowing wooden splint (flame has been blown out) and place it in the test tube with oxygen. The splint will flame up in oxygen


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