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Home School Life Journal ........... painting by Katie Bergenholtz
"Let us strive to make each moment beautiful."
Saint Francis DeSales

The Chemical Compostition of Water

Even the younger chemists know the formula for water- H2O,
but do they really know what that means? This is a great experiment to show them what it means. For this experiment, you will need two test tubes, a 9-volt battery, some Epsom salts and a bowl of water that is deep enough so that when it is nearly full of water, the battery can stand vertically in the bowl and still be fully submerged in water. It also has to be wide enough that the test tubes can be submerged sideways. Add 3 tablespoons of Epsom salts to the water and stir to dissolve. (Don't worry if it doesn't all dissolve.) We will be using electrolysis by using the electricity in the battery to break the water molecules down into its constituent elements- hydrogen and oxygen. The salt will help conduct the electricity.
Stand the battery up in the bottom of the bowl. You will see bubbles forming on each terminal immediately. Wait a few minutes so that the air bubbles trapped in the battery can be released as they are not part of the elements from the water.
Take the test tubes and fill them completely with the solution in the bowl by tilting them sideways, releasing all the trapped air, and filling them with the water-salt solution. There should be no air bubbles left in the test tubes. As simultaneously as possible, place one test tube over each terminal of the battery, making sure that the tops of the tubes are always submerged in the solution.
As time goes on, the gases produced at the terminals will be collected at the top of the test tubes.
You can take turns holding them, as long as you don't disturb the set-up.
You should see that hydrogen gas forms over the negative terminal and oxygen forms over the positive terminal. And you should see that there is about twice as much hydrogen gas in the one test tube as the oxygen gas in the other. Now you can explain the what the chemical formula means because they can see that there is two hydrogen atoms for every one oxygen.

(Exploring Creation with Physical Science Exp. 1.1, Exploring Creation with General Science)


  1. Huh, that's a cool way to break down the chemical.

  2. This is on my list of to-do's - we saw it on rough science, but there he lit the gas - the oxygen let the flame burn brightly, and the hydrogen exploded! I'm not sure I'm that brave, but I like the two to one demonstration.

  3. Oh how fun!!!! I remember doing this experiment with my children!

  4. Not for the faint of heart :) I remember doing this experiment in school lab, and it was fascinating. I am not sure I'd be brave enough to try it at home.

  5. That is why I got hubby to do it. :)


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