Electricity from fruit (cont'd)

Hi Alexia. I'm always happy to try to help kids over the little hurdles that may trip them up. But unfortunately, your questions are not those little hurdles :-(

Your questions are just exactly the kind of questions that teachers write to us about and beg us not to answer! Your teacher wants you to clearly understand the assignment, then struggle to think through the answers. If somebody else does the thinking, and you just execute the mechanics of it, you're learning to follow directions (which might be appropriate for some different class) but you are certainly not practicing science. Go back to your teacher and tell him/her what you don't understand about the assignment. And when s/he has had this 2nd opportunity to hear what you get and don't get, s/he will make sure you understand what you're supposed to independently do. Good luck!

Regards,

A. Jeff, various acids may be involved, so let's just call the anion 'X', representing that the anion could be citrate or acetate or ascorbate or whatever, or a combination of several anions. Let's also ignore the fact that X might be monovalent, divalent or trivalent, thus making the acid HX, H₂X, or H₃X -- and just call it H₂X.

So, at the copper electrode, the acid dissolves some copper while releasing hydrogen gas: Cu⁰ + H₂X^-2 => Cu⁺²X^-2 + H₂^

At the zinc electrode, the zinc is exposed to the CuX: Zn⁰ + Cu⁺²X ^-2 --> Cu⁰ + Zn⁺²X^-2

During this process, some copper has moved from the copper electrode to the zinc electrode and started to deposit on it. It didn't move in metallic (Cu⁰) form, but in the two 'halves' of Cu⁺² + 2e^-, the positively charged ions migrating through the solution and the electrons traveling through the wire.

Good luck.

A. I found some info on single cells.

Definition- "1.A single unit for electrolysis or conversion of chemical into electric energy, usually consisting of a container with electrodes and an electrolyte; a battery. Also called electrochemical cell.
2.A single unit that converts radiant energy into electric energy: a solar cell."(www.dictionary.com)

Go to this link for some more information.

http://www.encyclopedia.com/html/b1/battrye1lec.asp

For more information on batteries, which is what this experiment demonstrates in a safer way; less concentrated acid, go to this website. (Very,very good if you want to know anything about batteries)

http://www.howstuffworks.com/battery.htm

Hope this helps to answer any of your questions.

A. Hello June. When you say you can't find any books on the project, it is probably because you are narrowing your focus far too much! Your library probably has dozens or hundreds of books that discuss electricity, and one or two of them is what you need. See . . .

While your project will hopefully answer the question of whether a lemon, orange, or grapefruit conducts electricity best, if that was its only purpose it would be trivial, trite, and silly. Its purpose is actually to help you acquire a deeper understanding of electricity (and possibly physics and chemistry). And, of course, how to conduct science experiments. Ask your librarian for a couple of chemistry or science books at your reading level that discuss electricity, conductivity, resistance, electrons, or ions. Use them to try to better understand for yourself what this project should be achieving, and cite them. Good luck.

A. Hi, Marie. There should be no problem just using this wire to connect anything any way you want. The LCD clock needn't 'fit' on anything, just put a wire between the two things.

Got to Radio Shack or a similar place and get a tiny LCD (liquid crystal display). This should cost under a dollar, will require little power to illuminate, and your lemons should be able to do it, as shown in the youtube video.

Galvanized zinc roofing nails really would be better than can lids. Good luck.

A. An orange or a lemon doesn't actually "produce" any electricity at all, Daniel. It simply provides a liquid path that can conduct electricity. The difference in electrochemical potential between copper and zinc is what produces the electricity.

LED's vary, and you may need to connect several cells in series to light an LED. This excellent youtube video says you'll probably need 4 lemons in series --

A. pH doesn't directly affect the voltage because it doesn't, Jeff. The "half-cell" voltage depends on the metal in question, and the cell voltage is simply the sum of the two half cell voltages. So you can look up the half-cell voltages of each metal, and sum them. In the case of copper and zinc it should come out to 1.1 volts, but you have resistance in your circuit that is lowering this, and/or your voltmeter is drawing enough current to cause these lowered readings.

pH is literally "the negative log of the hydronium ion concentration". For high schoolers who have studied logarithms, this should be comprehensible. For somewhat younger students who understand the concept of hydrogen and of ions, pH is the concentration of hydrogen ions. For younger students still, it's how acidic the solution is, with 0 being fully acid, 7 being neutral, and 14 being fully alkaline. Best of luck.

A. What is it that you are being asked to determine by experiment, Xaijah? You shouldn't ask for the result of the experiment before you do it, and then try to make your experimental results match the result you are "supposed to get". That is "junk science" and your teacher might fail you.

It would be a good experiment to see if the size of the potato effects the length of time the clock will run. I don't think it will.

! No, You're right that wasn't really what I was trying to ask, but I did the experiment and found that the size doesn't really matter, or it would take longer to determine this than I had time for.

Xaijah N [returning]
- Prescott, Arizona

A. Hi, Wendy. If you have a bucket of water for watering your flowers, you can choose to pour it slowly for a relatively long time until it is empty or you can choose to pour it fast for a shorter time until it is empty. Still the bucket will go empty, so you can't choose to pour it fast and for a long time :-)

The fruit or vegetable is not the battery. The copper and the zinc and the fruit together are the battery. Copper metal moves from the penny to the zinc in two "halves": the positively charged copper ions flow through the fruit from the penny to the nail and the negatively charged electrons (the electric current) flow through the wire from the penny to the nail. The total amount of electricity available is limited by the penny losing its copper plating or the nail becoming completely copper plated because once both electrodes are covered with the same metal you no longer have a battery.

So if the current flows faster in one case, it can only flow for a shorter time before the battery goes dead just like the bucket goes empty sooner if you pour faster.

Regards,

A. Hi, Joe. The theoretical voltage available from the copper metal / zinc metal pair is 1.1 volts. Please look up the EMF series and confirm this. If you had a large sheet of copper spaced very close to a large sheet of zinc, with a perfectly conducting acid between them, no resistance in your wiring, and a meter that did not suck up any of your power, that is the maximum voltage you could ever obtain from that particular pair of metals.

You say the potato voltage is greater, but I am not at all sure that a potato consistently produces more voltage than the lemon. You need to put numbers on it, repeat the experiment several times, and make certain that you understand the difference between voltage and amperage before your question can be answered. What did you read for each in 5 trials?

The potato could be bigger, allowing more electrolyte to carry the current. Cut it to 1/4 its size and measure the voltage again; the penny & nail could have been closer together; the wires could have been shorter, etc.

I explained why the battery loses its charge faster if it's producing more current by speaking of a watering can: it holds only so much water, so the faster you pour, the sooner it will be empty. You have only so much surface on your nail and penny, the faster the copper ions move towards coating the zinc, the sooner it will be coated and the "battery" will be dead.

Regards,

A. Hi, Jacob. Liquid crystal displays like on calculators require very very little current (a dime-sized watch battery can power a watch and its LCD display for a year or more). You haven't told us anything about this clock, but it appears that it requires more current than your fruit batteries can generate.

Voltage is similar to water pressure, while current is similar to the flow rate of water. A garden hose may have as much water pressure as a good sized waterfall as long as you let very little water flow out of it. But you can't power a big water wheel or electric turbine with a garden hose, and you may not be able to power your clock with your fruit battery.

Fruit batteries generate about 0.8 to 1.0 volts, so it sounds like you are hooking up about a half dozen in series to get 5.65 volts. You can also connect fruit batteries in parallel to get more current.

Regards,

A. Hi, Gwen. I do not think that apples are alkaline. Did you test them with pH paper, or research the matter to be sure your statement is true? But alkalines can be excellent conductors too.

Lye (Drano) is much too strong and much too dangerous to be used in a child's science project, but it is very highly alkaline and an excellent conductor.

Fruits and vegetables contain hundreds of different exotic chemicals including chelators, complexors, sequestrants, surfactants, etc. It's not strictly an issue of acidity. When we don't even know what chemicals are in an experiment, trying to explain their effects on the experiment is questionable. Although using fruits and vegetables instead of controlled reagents can help bring safety into the science department, it unfortunately helps throw science out of the science department :-)

The best thing to do may be to learn how to conduct science projects, and what the scientific method is, and explain what you can, while leaving for later some of the explanations of why certain quirks happen the way they do if there are too many unknowns and variables to confidently explain it. Your son's "explanations" may or may not be correct, but his "observations" are correct, because observations are facts. So have him concentrate on his observations, but go light on conclusions :-)

Regards,