How can water be decomposed

Matter also does not disappear, although it can appear to. For example, in the electrolysis of water, although the volume of liquid water decreases, the matter that makes up the water is not disappearing. Rather, the hydrogen and oxygen atoms in the liquid water are being converted into molecules of hydrogen gas and oxygen gas.

This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. Composing and Decomposing Matter. NGSS Performance Expectations: MS-PS Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.

HS-PS Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties. The content and activities in this topic will work towards building an understanding of how the properties of substances change in a chemical reaction. Chemical Reactions Compounds are made of atoms of two or more elements joined chemically.

Weird Science. Further Investigations. Table of Contents: Composing and Decomposing Matter. Activity: Electrolysis of Water. Activity: Hoffman Apparatus. Special Features:. Representative Image:. Further Investigations: What is an Invertebrate?

Question Set: What is a Mammal? Further Investigations: What is a Mammal? Share and Connect. We invite you to share your thoughts, ask for help or read what other educators have to say by joining our community. Partner Organizations. Professional Development. Purchase a membership! The middle tube has a funnel-like section at the top called a thistle tube that is used for filling the apparatus with the water that will be electrolyzed.

Splitting water into its two components is much easier to do and is called water electrolysis. Making hydrogen or oxygen this way seems simple. But as you probably suspected, this reverse reaction needs an energy input, which is why it is also called an endothermic reaction. In water electrolysis, the source of energy used for the reaction to occur is electricity. An easy way to generate electricity is with a battery.

Because pure water is not good at conducting electricity, however, electrolysis requires the addition of an electrolyte , such as salt or acid. The electrolyte dissolves in water and separates into ions electrically charged particles that move through the solutions and are able to conduct electricity this way. To add electricity to the solution, you also need two electrical conductors that make contact with the water.

These are called electrodes and are mostly metals or other conductive materials. You can see this for yourself in this activity and even capture both gases! Observations and results Were you able to split the water into hydrogen and oxygen gas?

Did you see a lot of bubbles being produced at both of the graphite pins? Initially, when you put the cup with distilled water on top of the battery, you probably did not see much happening at the graphite electrodes.

This is because distilled water does not conduct electricity very well, therefore no or only minor electrode reactions are possible. If you add electrolytes such as baking soda, however, the added ions can conduct electricity and you should have seen gas bubbles emerging at both of the graphite pins. On one side, at the positive pole, oxygen develops whereas at the negative pole, hydrogen is produced.

When you looked closely, you might have observed that on the graphite electrode connected to the negative pole of the battery more gas was formed than on the other side. Collecting the two gases with the jumbo straws probably demonstrated this even better. After 10 minutes the water level at the negative pole should have been about half that of the positive side, meaning that you collected about double the amount of hydrogen gas compared with oxygen.

The difference is due to the fact that one water molecule has two hydrogen atoms to one oxygen atom, as explained above. This means it takes two water molecules 2 H2O to make one oxygen molecule O2. At the same time, however, two molecules of water 2 H2O can make two molecules of hydrogen 2 H2. You can visualize this by putting a pH strip into the solutions in the jumbo straws above each electrode.

The solution in the straw that was put on top of the negative battery pole electrode should show a basic pH 7 or greater whereas the other one should be acidic pH less than 7. Other electrode reactions can happen, too, if there are ions in the solution that compete with the hydrogen or oxygen production.

You might have observed once you added salt sodium chloride to your electrolyte, it started smelling like at a swimming pool. Instead of oxygen, chlorine is produced at the positive battery pole, which is also used for disinfection of swimming pool water. If you used metal thumbtacks as electrodes instead of graphite pins, the metal usually steel or brass will dissolve, or corrode, at the positive battery pole and instead of or in addition to gas production, you should see that the metal thumbtack turns reddish brown.

This demonstrates that electrolysis is not only a technique for splitting water into its components but can also drive other reactions that otherwise would not occur spontaneously.

Cleanup Clean up any spills with a towel. Pour the water with the electrolyte baking soda or salt down the drain. Remove the electrodes graphite pins or metal thumbtacks from the cups and put them into the trash. Throw the plastic cups and the sealed jumbo straws into the trash. You can reuse the nine-volt battery. This activity brought to you in partnership with Science Buddies.

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See Subscription Options. Discover World-Changing Science. Key concepts Water Chemistry Electricity Molecules Introduction You use it every day and cannot survive without it—no it is not the Internet, but water! Materials Waterproof work area Adult helper Mechanical pencil graphite thick enough that it does not break —or a wooden pencil and a knife with which to have your adult helper extract the graphite Glue Play-Doh or other clay Two or three disposable plastic cups Clear plastic ounce cups work best.

Scissors Permanent marker Two metal thumbtacks Distilled water Baking soda Nine-volt battery Two transparent straws jumbo size Teaspoon Medical dropper Timer Paper towels pH test strips optional Table salt sodium chloride—NaCl optional Preparation Your work area should be waterproof; water spills might happen during the activity.

Collect your sturdy mechanical pencil graphite. Make sure you have two pieces of about 2. If you choose to use a wooden pencil, have an adult take the knife and extract the graphite lead from the pencil. For this you should also get two pieces of about 2. These will be your graphite electrodes. With the scissors, carefully cut or have an adult cut around the open end of one plastic cup so it is the height of the nine-volt battery.

Dalton was an intensely religious man, devoted to his work with his only recreation being lawn bowling on Thursday afternoons. Some have suggested that it was the wooden balls banging into each other that gave him the idea of the atomic theory! Want to comment on this article? Visit our FB Page! Enter your keywords. Sign-Up Here. The principle of conservation of mass comes into play. General Science.