Extending my existing lemon power project

[Jacomay Schickerling]

Last year I did a project for the National Science Fair of Namibia which aimed showing that acidic fruits can not only chemically generate an electric current, but such current can vary at different temperatures and by using different electrode combinations. I also applied the information obtained during my research by connecting one of the fruits (lemon) to a LED lamp as proof that everything is not lost when you run out of batteries. I used lemons, oranges & tomatoes with electrode combinations of copper & zink, copper & magnesium and copper & steel at temperatures which varied between -10 and 27 degrees celsius. I won a gold medal (94%) at the nationals for this project. This year I would like to use this project as basis for my project, furthering by furthering my studies and experiments. I however has a problem in identifying how to further my existing project. I thought of using the knowledge obtained from last year's project to build different circuits (series & parallel) in powering different appliances with acidic fruit indicating what type of circuit (and with what amount of fruits) works best for each different appliance. I also thought of using a capacitor in my experiments, but is really unsure of the different possibilities there are, specially having regard to the fact that I have to meet a certain standard suitable for a grade 10 learner. It keeps on feeling as if my project need a lot of depth. Could you perhaps assist with ideas.

[Ceal Craig]

Last year I did a project for the National Science Fair of Namibia which aimed showing that acidic fruits can not only chemically generate an electric current, but such current can vary at different temperatures and by using different electrode combinations.... It keeps on feeling as if my project need a lot of depth. Could you perhaps assist with ideas.

Couple of thoughts:
1) For different fruit, current and voltage, how those vary with temperature and teim. (could use a multimeter to measure specific voltages and currents, then you could calculate resistance, or instead put a known load to test the power you could get.
2) Test these with different times and electrodes.

Bottom line, capture more specific quantitive data, to create graphs and tables.

Ceal Craig
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[Ceal Craig]

In addition, you could measure the pH of the fruits and investigate the different specific acids in these fruits.

Ceal Craig
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[Jacomay Schickerling]

Thank you very much for your quick response. In the project that I did last year I did capture all measurements pertaining to PH Levels of each individual fruit used, the different voltages and resistances with each type of fruit at 3 different temperatures with each of the mentioned electrode combinations used. I then drew a table where all the different information were displayed and subsequently used the following graphs in my survey: (1) PH Level graph of all the fruits used (30 fruits in total, excluding the fruits used in the parallel and series circuits powering the LED lamp); (2) Reaction of different fruits under different temperatures in respect of resistance; (3) ) Reaction of different fruits under different temperatures in respect of voltage (4) Comparative study between the different electrode combinations at the same temperature of the same fruits in respect of both resistance and voltage (5) Impact of series circuit in respect of both resistance and voltage (6) Impact of parallel circuit in respect of both resistance and voltage. Having thus already dealt with everything you mentioned in your answer, I am still desperately in need of more ideas to expand my existing project.
I do realize that it is very difficult to advice me with so little information of the exact content of my existing project and include therefore also an extract from my conclusion to assist.
My hypothesis, was that fruits containing a higher acidity level, at a cooler temperature and connected to the copper and magnesium electrodes, will conduct electricity the best because the higher the acidity the more hydrogen gas and heat energy will be released and the lower the temperature, the lower the resistance of the fruit and the higher the activity of the metal used as electrode, the higher the potential difference produced.
From my research I established that by using magnesium tape and a copper conductor with one lemon I could produce a potential difference of approximately one volt. If regard is had to the results of experiment 1, I have proved that all three types of fruits used and at various temperatures, succeeded in producing a potential difference in excess of 1 volt.
I ascertained that of the 3 fruits used in my experiments, lemons had the highest acidity level and on average between all the experiments, performed the best in respect of both volts and amps.
My experiments however indicated that, to the contrary of my hypothesis, that tomatoes, which had the lowest acidity level performed the best at freezing temperature in respect of volts, and with the exception of the magnesium – copper electrode combination also in respect of amps. Despite additional research and various enquiries to the people interviewed, I could find no explanation for this peculiar phenomenon.
Ifound that since magnesium is much more active than zinc and steel, the potential produced is much higher than with zink and steel. This was then also the reason, why I used the magnesium-copper electrode combination for experiment 10.
I wanted to be able to use the current generated to power an easily obtainable item such as a flashlight globe. The problem that I encountered was that although the number of cells wired in series measured the required minimum volts, it failed to generate sufficient amps. To bridge this problem I linked three, 3-cell series circuits in parallel. By this I succeeded in getting the amps up to 1.6730, but it was still not enough to light the globe. I was unable to establish the exact reason for that although I suspect that it is most probably the result of resistance in the lemon cells itself.
I however did not experience any problem whatsoever with the powering of the LED lamp, where three lemons were required to get the required result. Although not part of our aim, it may be mentioned that I also encountered no problem to power various other digital items, inter alia a calculater. The light emitted by the LED lamp can be observed without any difficulty whatsoever.
The lemon cell is peculiar in that both oxidation and reduction take place at the same electrode. The anode metals become oxidized and the hydrogen ions in the lemon are reduced to hydrogen gas in part, at the zinc and magnesium electrode where the hydrogen gas can be seen vigorously bubbling out from around the Magnesium electrode.
A peculiar aspect of my experiment was that voltage and amp readings in frozen lemon cells slowly increased over a period of 15 to 20 minutes before starting to reduce. I found that such a cell certainly has a longer life than one initiated at room temperature.

[davidmoilanen]

It sounds like you've really studied this system extensively with regard to the different fruits, pH, temperature, etc. I don't know whether there are too many other variations you can do.

However, here's an idea that you might want to consider. You mentioned that the hydrogen gas bubbled out at the position of the electrode. It seems reasonable to if you could collect the gas you could use the change in volume of the gas with time as an indicator of the rate of the reaction. This would be interesting because it would allow you to relate the voltage that the fruit was producing with the chemical potential of the reaction and the rate at which the reaction was occurring. You may already know a lot about chemical potential and the relationship between it and electrical potential but if not, see if you can find some information about the Nernst Equation and read about it.

You will have to figure out a way to accurately measure the volume of hydrogen gas that evolves. A method that might work is to try to direct the gas through some tubing into an inverted piece of volumetric glassware filled with water. This is best done in a sink with the glassware under water as well. The displacement of the water tells you the volume of the gas collected. This experiment would also require some knowledge of the ideal gas law which you can find in any introductory chemistry textbook.

Comparing the voltage that you measure with the rate of reaction and the chemical potential that you determine based on the reaction you think is occurring in the fruit should allow you to make some conclusions about the reaction and whether or not there is resistance in the fruit as you suggested.

Good luck with the project, it sounds like you have many good ideas and dedication as well. I hope my ideas help you come up with some more of your own.

David