Hoffman Water Electrolysis Unit (Megan Whitaker)

Author

Megan Whitaker- Physical Science Teacher, Pacoima Middle School

Principles

Water is made up of oxygen and hydrogen atoms that form molecules.

The atoms can be separated using an electrical current.

When the hydrogen and oxygen atoms are separated they are in the gaseous state.

Standards

.8.3b- Students know that compounds are formed by combining two or more different

elements and that compounds have properties that are different from their

constituent elements.

8.5a- Students know reactant atoms and molecules interact to form products with

different chemical properties.

8.5b- Students know the idea of atoms explains the conservation of matter: In chemical

reactions the number of atoms stays the same no matter how they are arranged,

so their total mass stays the same

Materials needed

Hoffman Electrolysis Unit

Power Source

Water

Procedure

1. Fill the center tube of the Hoffman Electrolysis unit with water until the two outside tubes are partially filled.

2. Connect the leads to the DC battery power source and turn on the power.

3. Bubble will start to form on the leads in the outer tubes.

4. One tube will fill twice as fast as the other tube due to the structure of water molecules (2 hydrogen and 1 oxygen).

Explanation

The process of decomposing water into its component atoms and molecules using electrolysis shows students that water is composed of two separate elements which, when separated, are in the form of colorless, oder-less gases. Water has a molecular structure of 1 oxygen atom bonded to 2 hydrogen atoms.

Questions

1. Based on the volume of gases in each tube, what do you think the ratio of oxygen to hydrogen is in the water? The ratio of oxygen to hydrogen is 1 to 2 in each molecule.

2. Why is electrolysis required to separate the gases from the water? Why can't we do this with a knife or in a pan? Electrolysis is required to separate the hydrogen and oxygen gases because the bonds between the atoms are too strong to be broken physically. The only way to break the bonds is with the application of energy through the DC current from the battery. There is no knife sharp enough to go between the atoms in a water molecule and applying heat will cause the water to boil or evaporate (change state from liquid to gas).

3. How are the properties of the gases different from the properties of the water? Water is not combustible, it is liquid at room temperature, and when it comes into contact with a burning splint the splint will go out. Oxygen gas will cause a glowing splint to glow brighter and/or ignite, and hydrogen gas ignites when it comes into contact with a burning or glowing splint. When you mix the oxygen and hydrogen together and add a spark or open flame, the gases will explosively combine together again, releasing a large amount of flame and heat and creating a small amount of liquid water.

Everyday examples of the principles illustrated

In Industry:

• Production of aluminium, lithium, sodium, potassium, magnesium, calcium

• Anodization is an electrolytic process that makes the surface of metals resistant to corrosion. For example, ships are saved from being corroded by oxygen in the water by this process. The process is also used to decorate surfaces.

• Production of hydrogen for fuel, using a cheap source of electrical energy.

• Electrolytic Etching of metal surfaces like tools or knives with a permanent mark or logo.

Photos

Samples of Hoffman Electrolysis Unit

Sample of Electrolysis unit using classroom equipment (beaker, test tubes, electrodes)

Igniting Hydrogen and Oxygen Gases to recombine into water.

Movies

*Start at 1:12

References

Electrolysis of Water -NCSU Department of Chemistry

Electrolysis of Water - Wikipedia

Decomposition of Water- Wikipedia

Hoffman Electrolysis - Carolina Biological (Can be found in most catalogs)

DC Power Source - Carolina Biological (Can be found in most catalogs)