Electrochemical Cell

A) Objective: To introduce students to basic chemistry lab procedures. To discover how batteries work.

B) Time: Approximately 90 minutes.

C) Materials:

• List of materials (for one battery /wet cell):

  a) 3.5 g sodium sulphate powder	j) 10 cm strip of copper
  b) 3.5 g copper sulphate powder	k) 10 cm strip of magnesium
  c) 15 cm dialysis tubing*	l) Small scrub brush
  d) 50 mL graduated cylinder	m) Funnel
  e) 2 100 mL beakers or small baby food jars	n) Glass stirring rod
  f) 2 scoops	o) Weigh scale
  g) 2 weigh boats	p) Battery-powered gadgets
  h) Wire leads with alligator clips	q) (toys, alarm clocks, etc.)
  i) Safety glasses
  *Dialysis tubing should be wide enough to contain the copper strip.

• Materials found at: Borrow from high school or college/university labs. Chemicals, metals, dialysis tubing, glassware, and other apparatus can be purchased from a chemical supply company. Electronics shops (like Radio Shack) carry wire leads. Given sufficient time, companies may be willing to donate supplies. The gadgets (items p) used for testing the batteries can be brought from home.
• Cost per student: free if borrowed.

D) Theory:Batteries turn chemical energy (energy from chemical reactions) into electrical energy. The battery we make will work the same way as regular AA batteries, except it will be made with solutions instead of solid chemicals. Each wet cell should produce approximately 1.5 V, enough to light a small bulb. Several cells hooked in series should produce enough electricity to run a 9 V gadget for several hours.

There are two separate reactions taking place: one between the magnesium strip and the sodium sulphate, and one between the copper strip and the copper sulphate. The dialysis tubing keeps the solutions mostly separate, but allows electrons to move between them. The reaction on the magnesium strip attracts electrons; the reaction on the copper strip repells electrons away. So electrons move from the copper to the magnesium, creating an electrical current. We can see evidence of this when bubbles form in the solution - electricity passing through water splits the water molecules into hydrogen and oxygen gas (electrolysis).

We can attach wires to the metal strips with alligator clips, then touch the other ends of the wires to battery contact points in any battery-powered gadget. Wires may also be attached to the metal strips of other cells to create a series circuit (be sure to hook magnesium to copper to magnesium to copper...etc.). This will provide the gadget with more voltage.

E) Procedure:

1. Put on safety glasses.
2. Students should work in pairs and have an assigned workspace.
3. Fill one of the beakers with water and immerse the dialysis tubing in it to soften up.
4. Gently scrub the dull oxide off of the metal strips with the scrub brush.
5. Using the graduated cylinder, measure out 25 mL water and pour into the unused beaker.
6. Measure out another 50 mL water and leave it in the graduated cylinder.
7. Go to the weigh scales and measure out 3.5 g of copper sulphate into a weighboat.
8. Measure out 3.5 g sodium sulphate into the second weighboat.
9. Mix the copper sulphate with the 25 mL water in the beaker. Stir until dissolved.
10. Take the dialysis tubing out of the water and tie a knot in one end of it.
11. Gently open the other end of the tubing and insert the funnel.
12. Pour the copper sulphate solution slowly into the funnel, filling the dialysis tubing about 4 cm deep.
13. Remove the funnel and gently insert the copper strip into the tubing. Slide it all the way to the bottom of the solution and make sure some of the strip is sticking out of the tubing.
14. Dump out the water that the tubing had been soaking in. Fill the beaker with the 50 mL water from the graduated cylinder.
15. Mix in the sodium sulphate and stir until dissolved.
16. Place the tubing in this solution and rest it against one side of the beaker.
17. Place the magnesium strip in the solution and rest it against the opposite side of the beaker. Make sure the magnesium and the tubing do not touch each other.
18. Rest the rubber stopper in the top of the beaker to hold everything in place.
19. Look for bubbles of hydrogen and oxygen gas forming on the magnesium.
20. Using the alligator clips, attach wire leads to each of the metal strips, then touch the other ends of the leads to battery contact points in the gadgets. If nothing happens, reverse the leads.
21. If your battery isn't producing enough volts to power your gadgets, attach several batteries together using the wire leads. Make sure you link copper to magnesium to copper to magnesium....etc.

F) Safety:
The chemicals should come with highly specific safety information when you purchase them. To summarize:

• Copper sulphate and sodium sulphate are toxic. If ingested or inhaled, medical attention should be sought immediately.
• Safety glasses should be worn. If either chemical contacts the eye, it should be immediately rinsed with lots of warm water. Medical attention should be sought.
• Small splashes on the skin are not dangerous, but they should be rinsed off with soap and lots of water right away. If the chemicals soak into clothing, the clothing should be removed immediately and the skin rinsed with lots of water. If there is extensive contact with the skin, medical attention should be sought.

G) Real Life Examples:Batteries run out of electricity when the reacting chemicals in them are used up. Rechargeable batteries run on chemical reactions which can be reversed (like a cassette being rewound). They are plugged into a recharger which sends an electrical current into them, reversing the reaction and recreating the starting chemicals. The battery is then ready to power things up again.