Lab 21: Electrochemistry

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Experimental Title: Lab 21:  Electrochemistry

Date of laboratory:  October 28, 2014

Purpose: The purpose of this laboratory is to investigate electrolysis of water and to produce electricity via a chemical reaction in a lemon battery.

Introduction:

Electrochemistry is the relationship between chemical energy and electrical energy. If you would like to learn more, be sure to review the second half of chapter 16 in your textbook.

Electrochemistry involves two separate processes:

1. Utilizing electrical energy to cause a chemical reaction to occur. An example is electrolysis, during which electricity is used to split water into oxygen and hydrogen gas.

The reaction for the electrolysis of water is
2H20 → O2 + 2H2

test-tubes

2. Using a chemical reaction to produce electricity. An example is a lemon battery, which can be used to produce enough electricity to light up a LED (Light emitting diode).

Check out this animation showing the movement of electrons between zinc and copper in a galvanic cell (Takes a few seconds to load.) A similar reaction takes place within the lemon.

How to make a lemon battery:

See the Hila Website for more instructions for making a lemon battery.

Special safety concerns for Lab 21:

  • If anything spills, please clean it up immediately with a paper towel and let your instructor know.
  • If glass breaks, do not pick it up with your bare hands. Notify your instructor immediately.
  • Be sure to wash your hands when you are finished with this lab
  • Avoid touching the battery with wet hands and don’t touch both terminals at once to avoid shocks.

Materials:

  • Magnesium sulfate (Epsom salts)
  • 9 Volt battery
  • Battery adapter
  • Glass beaker
  • 2 test tubes
  • Water
  • Graduated cylinders
  • Transfer pipette
  • Rubber band
  • Stoppers
  • Wood splint
  • Matches or butane lighter
  • Lemons
  • Zinc
  • Copper
  • Wires
  • LED (Light emitting diode)
  • Spatula (measuring)

Procedures:

Part 1.  Electrolysis of Water

1. Obtain a 250 mL glass beaker, 9 volt battery,  2 test tubes, magnesium sulfate, a rubber band, and the batter adapter with wire leads.

2. Add about 200 mL of water to the glass beaker. Add a heaping spatula full of magnesium sulfate to the water. Stir until it is dissolved.

3. Place the two glass test tubes side-by-side. Wrap with a rubber band to hold them in place.

4. Over the sink, fill the test tubes with the magnesium sulfate solution, trying to prevent bubbles from forming. Stopper the tubes with rubber stoppers.

5. Invert the tubes into the beaker and remove the stoppers, keeping the tubes submerged. If you have difficulty manipulating the stoppers in the beaker, try putting your thumb over a single filled test tube (like we did last time) and then transfer the tube into the beaker and release so the open end is submerged and no bubbles are trapped in the top. Hold the tube upright and repeat with the second tube.

6. Have a helper hold the tubes while you run the leads of the battery adapter into each test tube, red into one and black into the other. Do not submerse the adapter itself.

7. Connect the 9 volt battery to the adapter part. Pay attention to which ends are in which test tubes.

Observations:

8. Remove the battery when one test tube is filled with gas. Stopper each test tube under water to preserve the gases inside.

Optional:  Take the test tubes outside with the wood splint and lighter. For the tube with less gas in it, light the splint and then blow it out. Place the glowing splint near the opening of the tests tube and release the stopper.

What does this show?

Now, light another splint and hold it near the opening of the test tube with more gas, and remove the stopper. Note:  be prepared for a pop sound, so don’t be startled.

Part 2.  Lemon Battery

We will follow the instructions in the above video and website (linked in the introduction section) to put together and test a lemon battery.

Conclusions:

Once you have completed the parts, sit down and write a sentence or two to explain the results.

Discussion:

Record any thoughts you have about the experiments, including:

  • Possible improvements to the procedures or how to tweak techniques
  • How the results differed from your expectations
  • Suggestions for other experiments

Please leave a comment or send an e-mail if you have any questions before our meeting.

 

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