The lemon cell 4.

EQUIPMENT:

• Lemons

• Wires (2 per lemon)

• Crocodile clips (as many as you have wires)

METHOD:

1. Soften the lemon slightly by gently squeezing and rolling it to loosen the juice.

2. Push 1 x copper and 1 x zinc strip into the cut surface (in contact with juice) as far from each other as possible (at least 5 cm and not touching each other).

3. Attach a crocodile clip to each metal strip and attach a wire to each crocodile clip.

THE SCIENCE BIT…

• Copper strip/wire

• Zinc strip/galvanized nail

• Multimeter

• LED

4. Attach the end of each wire to a multimeter set to amps/milliamps.

5. Once you have set up 1 lemon cell, you can attach more lemons in the same way, linking them in series with each other (not in parallel).

6. Swap the multimeter for an LED and, if the lemons have enough power, you will see the LED light up.

The lemon battery works in the same way as electrolysis. The acidic lemon juice (citric acid is the weak acid in lemon juice) is the electrolyte solution, able to carry a charge, and the zinc and copper strips are the anode and cathode electrodes. The lemon provides the power and the circuit is completed by the connecting of the wires and multimeter.

Zinc dissolves in lemon juice, leaving zinc ions (Zn2+) in the juice, while the two electrons (per atom) move through the wire toward the copper. The following chemical reaction represents this oxidation reaction:

Zn → Zn2+ + 2e−

The copper doesn’t dissolve in the juice, and the citric acid (in the juice) partially dissociates, leaving some H+ ions behind. These combine with the electrons at the copper (that arrived from the zinc), to form hydrogen gas, which leaves the system.

This reduction reaction is shown by the equation:

2H+ + 2e → H2

You might be able to see the hydrogen bubbles at the copper electrode if you swap out the lemons for lemon juice.

Hopefully you will get a voltage of around 1.3 V (but very few amps) for the lemon battery.

OTHER FRUIT AND VEG TO TRY:

• Any citrus fruit: orange, lime, grapefruit, or straight fruit juice.

• Potato (phosphoric acid instead of citric acid provides the H+ ions).

You could have some fun building the BIGGEST fruit and vegetable battery you can, and see how much power you can get, or have a fruit battery building competition and award a prize for the most LEDs lit.

The properties of PYREX® are such that it is possibly the most versatile glass around. It can be safely used over a temperature range from -192°C to +500°C, it has excellent chemical resistance to even the most aggressive acids and bases and both factors have made it the first choice in some of the most demanding scientific applications.

In the school environment PYREX® is an ideal choice because of its resistance to heat. There is far less chance of breaking and ‘hot spotting’ on beakers, flasks and test tubes being heated, and therefore it is a safe alternative to cheaper, less resistant glassware in the market.

PYREX® is made of Borosilicate glass 3.3. The glassware is protected against thermal breakage and mechanical shock because of the slow and careful annealing process during manufacture, and the chemical resistance of PYREX® is excellent, making it an ideal storage container for all your acidic or basic solutions.

The chemical resistant labelling ensures longevity of your glassware, especially pieces that are regularly in the dishwasher. The labelling is clear and a good contrast to show up well whatever solution is inside the container, especially useful when measuring and using equipment like burettes.

THE NAME PYREX® WAS DERIVED FROM THE LATIN: PYRO MEANING FIRE AND REX, MEANING KING – AND NOW YOU CAN SEE WHY!

To find out more about key features of PYREX, visit our Resource Hub and download the table!