Batteries

Objective:

The objective of this lab is to learn about batteries, how they work and what they are used for.

Background on

Have you ever wondered what gives your watch or phone the energy it needs to constantly run? Just like us machines need energy to move their parts and perform the different tasks we ask them to do, but machines cannot eat food to get the energy they need to run, so how do they get that energy? The answer is electricity and for things like our phones and watches electrical batteries!

Before we get into all of the amazing things batteries can do let’s learn about the different parts of an electrical battery. A battery consists of one or more cells, connected either in parallel, series or series-and-parallel pattern.

• Parallel (meaning side by side)
• Series (meaning one after another)
• Series-and-parallel (meaning side by side and one after another)

Each cell contains half cells, half cells separate the reactants so that the reaction can be controlled. By connecting the two half cells, a reaction occurs that causes electrons to travel from one side to the other in the half cells, this movement of electrons excites other molecules along the path between the half cells (i.e. the wire that connects the two ends).

In most of the batteries that you see a basic zinc (Zn) and copper (Cu) reaction is being harnessed. Since the reaction with zinc metal (ie the reactant of the oxidation reaction) is providing the electron required to reduce the copper, the zinc is the reducing agent and the zinc itself is oxidized. Copper ions in this case are the oxidizing agent - they oxidize the zinc and are themselves reduced. In this type of reaction the material at the Anode is Oxidized and the material at the cathode is Reduced. In a standard battery the copper is at the cathode and the zinc is at the anode with electrolytes in between

When you connect the anode and cathode together the chemical reaction that is contained in the battery is able to proceed. Think about a battery just sitting on the counter, in this instance the anode and cathode are not interacting so the battery will not produce any energy or have the reaction proceed. Now connect the anode and cathode, now that they are connected the reaction can proceed and the battery will produce energy. If the battery has enough energy it can make things like lights light up or gears turn. 

Voltage (V) is what makes electric charges move. It is the 'push' that causes charges to move in a wire or other electrical conductor.  Most batteries (AAA, AA, C, D) are 1.5V, but an LED light requires around 3V to make it light up, so you put multiple batteries together in series (1.5V + 1.5V = 3V) to light the LED.

Many batteries that we use in toys and lights are disposable. This means they are sold fully charged and are designed so that the chemical reaction proceeds in only one direction, when the reactants are used up the battery will no longer work to power things and needs to be thrown away. As disposable batteries can be very wasteful we have developed rechargeable batteries. These batteries use other oxidation-reduction reactions that can easily be reversed to recharge the battery many times, allowing the battery to be used over and over without replacement.

Batteries are used in so many things from our cars to our phones to watches and toys. We use the energy stored in batteries everyday to make life easier and to be able to take more fun on as we travel around. Batteries harness chemistry in a controlled reaction and allow for mobility of electrical devices!

Materials

• Pennies
• Washers (zinc plated i.e. galvanized)
• Fruits and Vegetables (lemons, potatoes, etc... typically two to five of each)
• Alligator clip testing wires (insulated copper wires with alligator clips on each end)
• LED light (just a single bulb is best)
• plastic knife to pierce fruits and vegetables

Method

Prepare Experiment

• Collect all of the materials that you will need for the experience and set them in front of you neatly and organized.

Run Experiment

1. Hand out materials to each child (1 knife, 1 lemon, 1 penny, 1 washer, two alligator clip test wires, 1 LED light) (we use team captains at each table to do this task, but it is always good to check that they have handed out each material)
2. Carefully pierce near the end of the lemon with the knife
3. Remove knife and place the penny in the hole created by the lemon, insert the penny so half of it is still sticking out of the lemon
4. Following the line created from the end of the lemon to the penny pierce the lemon at the other end with the knife
5. Remove knife and place the washer in the hole created by the lemon, insert the washer so half of it is still sticking out of the lemon
6. Attach alligator clip wires to the LED, one on each metal lead
7. Attach the other end of one alligator clip wire from the LED to the penny
8. Attach the other end of the other alligator clip wire from the LED to the washer
9. Does the LED light up? If not try switching which wire is connected to the penny and washer, does it light up now?
10. If it does not light up try adding another lemon that has been setup following steps 2 through 5
• When connecting the lemons together you will connect them in series (one after another) and connect the penny to the washer on the other lemon (this is super important connect opposites!)
• The penny on one lemon will connect to the LED wire and the washer on one lemon will connect to the other LED wire
• Once everything is connected does the LED light up?
11. Try flipping the LED wires from the penny to the washer and vice versa, does the LED light up?
    
12. Repeat Step 10 with up to 5 lemons, does your LED light up?
13. Repeat steps 2-11 with potatoes or pickles or tomatoes, do you have a different result?

Analyze Data

Were you able to get the LED to light with just one piece of fruit or vegetable that contained an anode and a cathode? What about two? How about three? Do you think it would work if you mix the fruits and vegetables?

Conclusions

Batteries can be made out of many different substances. This lab is escpecially fun as the kids can use all sorts of things from tomatoes to lemons from potatoes to pickles. In most instances we needed at least 3 fruits and vegetables to build up a large enough voltage to light the LED.

Make It Your Own

Next time try using a large anode and cathode, i.e. use a strip of copper and a strip of zinc. How did your experiment change?

Extension Activities to do at home

If your parents have extra pennies and galvanized washes and some copper wire, try making your battery using some other materials. Will a battery work if it is put into dry flour? Now try putting the copper and the zinc into some vinegar. You may notice that some form of acid is needed for the battery to work properly and not everything in your pantry will make a proper battery.