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Title: Splitting Water: Homemade Hydrogen
Principle(s) Investigated: Law of Conservation of mass, Electrolysis- Separation of elements, Solubility and Electrical Conductivity of Ionic Compounds, Atomic structure of Elements
Standards : 8.3.b-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.
8.5.a-Students know reactant atoms and molecules interact to form products with different chemical properties.
8.5.b- 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.
9.2.a-Students know atoms combine to form molecules by sharing electrons to form covalent or metallic bonds or by exchanging electrons to form ionic bonds.
Materials:
Per Group
· 9V Battery
· Copper wire (x2 strips)
· Copper Nails/Rods (x2)
· Water
· Salt (to increase conductivity of water, but not necessary),
· 10-16oz. cup
· [Teacher Demonstration Option: Matchbook and small test tube to witness properties of gases made.]
Procedure: Estimated Run-Time: 45 minutes
Begin by prefacing the activity with an engaging question related to your lesson or what you want this activity to focus on. Draw in students by asking relevant questions to everyday life about the environment, our fuel economy, and/or our sources of energy. Establish several sources of renewable resources, chiefly water and hydrogen. [Powerpoint images]
Probe for students’ background knowledge.
Think-Pair-Share- Ask students to discuss with a partner What elements make up water? How we can use water or its constituent elements as a renewable source of energy?
Transition to lab experiment- Ask class if we can harness the power of Hydrogen element from water? (Distribute packaged materials to groups) Lets find out!
Lab:
Demonstrate for class how to set up battery apparatus for experiment.
1) Fill cup with water (Varies depending on size of container).
2) Add one tablespoon of salt to create a highly conductive solution of water.
3) Wrap one copper wire around each node of the 9V battery.
4) Wrap the end of each wire around two separate copper nails, creating two electrodes
5) Now you are ready to begin the experiment.
Have students repeat the procedure and begin their experiment.
a) Option: You can make this experiment a two-part procedure by first engaging a trial with only water, then create the salt-water solution to witness the effects of using a solution of an conductivity in a solution using an ionic compound.
Student prior knowledge: Structure of Matter: Students should know that atoms are made of protons, neutrons, and electrons, which have an electrical charge.
Types of Matter: Students should know that all matter can be classified as either elements, mixtures, or compounds, and understand that compounds are two or more different elements chemically joined together.
Covalent and Ionic Bonds: Students should understand covalent bonding occurs when atoms share electrons on their valence electron shell. Ionic bonding occurs when ions (electrically charged atoms) are bonded with each other through their electromagnetic forces.
Chemical Reaction/Law of Conservation of Mass: Mass can neither be created or destroyed, so that during a chemical reaction, particles are not being newly created, the atoms are merely being rearranged.
Explanation
This experiment demonstrates several different principles, which can selectively be discussed or investigated, depending on what concepts are trying to be explored or reinforced.
What is occurring in this experiment is a process known as electrolysis, which is the use of an electric current to produce a chemical reaction. In this lab, you are essentially splitting water (H2O) into its constituent elements; Hydrogen and Helium. Hydrogen and Helium are bonded together to form water by sharing electrons in what is known as a covalent bond. Two positively charged Hydrogen ions are joined with a negatively charged Oxygen ion because of the electromagnetic attraction between the two ions. When electricity is introduced to the water through two electrodes; a cathode (negative) and an anode (positive), the ions become attracted to the oppositely charged electrode, because the electrical energy you are placing in the water has a greater electromagnetic force than that which hold the ions together in a water molecule. The result is the hydrogen and the oxygen ions gain or lose electrons depending on their charge, effectively stabilizing themselves into electrically balanced atoms.
Since this process relies on the passing of an electric current through a medium to attract the ions, the effectiveness of the process is dependent upon the conductivity of you medium. Water itself is capable of passing an electric current. When mixing an ionic compound, such as salt, and water together, you are able to improve the conductivity of your medium. When an ionic compound (elements bonded together based on their electrical charge, resulting in a neutral charge), becomes dissolved in water, the Sodium and Chlorine ions separate into free floating ions. As free floating ions dissolved in water, the solution becomes highly conductive, capable of quickly passing an electrical charge. Salt itself, as a solid cannot pass an electrical charge because the ions (Sodium and Chlorine) are locked together, immobile and incapable of passing electrons quickly.
Chemical formula for Electrolysis:
energy (electricity) +2 H2O --> O2 + 2 H2
Questions & Answers:
1) Why are there only a few bubbles forming on one of the electrodes, and many forming on the other electrode?
The simple answer lies in the formula for water. For every molecule split, you yield one Oxygen molecule to two Hydrogen molecules. For a more in depth response, Hydrogen becomes attracted to the cathode (negative charge) because the hydrogen ions have a positive charge. Oxygen collects on the anode because an oxygen ion bears a negative charge.
2) How is the experiment different after you made a salt-water solution?
The production of bubbles is much more powerful and clearly visible. More oxygen and hydrogen are produced – the dissociated sodium and chlorine ions act as a catalyst, forming a “bridge“ so that the electricity can travel in a continuous circuit through the water.
3) How can you verify that hydrogen and oxygen are actually being split?
There are one of two ways to figure this out… Each water molecule (H2O) consists of two hydrogen atoms and one oxygen atom — or twice the amount of hydrogen atoms as oxygen atoms. Hydrogen is produced at the negative electrode, also known as the cathode. The electrode at which the most gas is produced is the cathode, containing hydrogen. Oxygen is being produced at the positive electrode, the anode., which has the least amount of gas is produced.
OR
You can collect the hydrogen gas in a test tube in your solution by placing it over the cathode. After sufficient amounts of the gas has been collected, place the mouth of a tube near a flame and listen for the *POP*!
Applications to Everyday Life:
Use of hydrogen for fuel: We know hydrogen is the most abundant element in the universe, with a variety of uses. Hydrogen can be used as a lifting agent, say, to make a balloon, or even a flying zeppelin! Hydrogen is more commonly used as a fuel source in batteries, know as a hydrogen-fuel cell, which leading scientists are working to make a more effective process so that we can shift from a Fossil Fuel (non-renewable resource) economy, to a Hydrogen (renewable resource) Economy.
Hydrolysis/Electrolysis, TomAto/TomAHto: The same process occurring in hydrolysis, separating elements of a compound, is the same that occurs in electrolysis. Electrolysis however, uses a different solution. The “solution” in electrolysis can include ore material, or an impure substance. By melting the ore and using electrolysis, you can extract the elements from an ore. This is of course very simplified here, but a very similar process occurs when extracting Aluminum, an element we very commonly see in our everyday lives.
Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.
Videos:
http://periodictable.com/Stories/001.1/Videos/Bubbles.MOV
http://periodictable.com/Stories/001.1/Videos/BubblesWithSalt.MOV
http://www1.eere.energy.gov/hydrogenandfuelcells/education/pdfs/activity_guide.pdf
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