mimi9000
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Another lemon battery question

Postby mimi9000 » Sat Mar 26, 2016 1:43 am

Hello! My 2nd grader is doing a science project that's a variation of the Batteries that Make Cents project.

He wanted to see which type of battery (lemon juice, vinegar, Coke, OJ) would power a clock the longest. Vinegar was the "winner" and Coke was a close 2nd.

I'm trying to figure out how and why this happened, in terms a 2nd grader would understand. Does an electrolyte's pH have anything to do with it? That is, the most acidic liquid powers the battery the longest?

I guess I'm also not understanding the electrolyte's role in this. We've read that the electrolyte block electrons form moving from the negative to positive terminal. But we've also read that electrolytes conduct electricity.

Any help is appreciated -- thank you!

p.s. In the experiment we used zinc and copper strips, connected by a copper wire.

324B21
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Re: Another lemon battery question

Postby 324B21 » Sun Mar 27, 2016 10:37 pm

Hi there.

I would happy to try and assist with this question. I am so glad he found an experiment that peaked his interest!

So--let me express first off that there is no wrong outcome in an experiment. The act of the experiment and the critical thinking is the most important part. With that said, here is the answer.

Concept: Copper is a great carrier of electricity (it is also really inexpensive comparatively). This is why copper wires were used for so many things for so long. You can still find copper in small motors and telecommunication.

The pH level actually doesn't have a ton to do with conductivity (I will explain more and circle back to this point--so let's put a bookmark here). What does is the number of 'free ions' available. A way to explain this concept might be to try the experiment for fun with deionized and ionized water (if you have access to ocean water then use this instead--you could always make some if you want to just whip some up using salt and water together 50/50). You should see no electricity conducted in the deionized water due to those important ions being removed while the ionized water/ocean water/salt water should conduct much more (salt is awesome for free ions). Thinking about it--you could even use deionized water first, then deionized water with salt added! Probe him about why he thinks he got those results. He might need a bit of help--but potentially not since he seems like a smart cookie.

So--now it is time to lay it out here. Vinegar is a terrible conductor. The reason is due to the number of free ions available being so low. The same by the way is true of lemon juice. Remember that the more free ions, the better the conductor. However, in comparison with coke and OJ, vinegar is going to take the prize for most conductivity.

It is time to pick back up with the bookmark I mentioned above. If you feel like the information I provided above is too advanced, then let me run off of your idea that pH = Conductivity (but perhaps print the full answer for when this experiment comes up again in a few years..because it will, and hopefully the more advanced information will make more sense then to your son). pH is on a scale of 0-14. 0 is the strongest acid while 14 is the strongest base. Acidity CAN to an extent affect conductivity. Strong acids like hydrocloric acid or battery acid (both are a zero) are amazing electricity conductors while liquid drain cleaner and oven cleaner (14) are awful conductors. Lemon juice and vinegar sit at a 2 on the pH scale, while OJ and coke sit at a 3. Saltwater by the way which conducts electricity really well due to the salt and water ions is an 8. So..based on your results things would be a bit off in the order. However, for this specific experiment and his age it should be fine to explain what happened either way this time around since there CAN be a correlation between acidity and conductivity.

I hope this helps and makes sense. Please feel free to send us another message if you need any clarification, or have other questions!

Elizabeth

mimi9000
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Re: Another lemon battery question

Postby mimi9000 » Mon Mar 28, 2016 11:32 pm

Hi Elizabeth,

Thank you so much for the detailed reply! Very interesting and informative.

We'll try the experiment using deionized water vs. salt water. Sounds fun.

I forgot to mention my son also tested blue Gatorade. It did power the clock but not for long and finished "in last place," as he put it.

To make sure I'm understanding this properly: all of the electrolytes we tested (vinegar, lemon juice, OJ, Gatorade, Coke) contain free ions, is that correct? And the electrolyte that has the most free ions generates the most electricity? When the ions are used up, the battery stops working?

I know I'm way oversimplifying but my audience is 7 years old. :D

Thanks again for your help!

324B21
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Re: Another lemon battery question

Postby 324B21 » Wed Mar 30, 2016 5:55 pm

Hey there.

This is a good way to explain it for that age group! I might suggest adding a bit more though...(If you think he can handle it), A bit more of a complex way to explain it would be to ask what all of these liquids you have tested have in common...(might suggest helping him out with the "deionized / deionized + salt experiment first).

The answer is water. The definition of an electrolyte itself hinges on that word: water. You can't have an electrolyte without it. (the word electrolyte is from the Greek meaning untie or make loose). Without the water you have no electric charge. Imagine trying to run electricity through baby powder versus soda. Water as I mentioned previously is a great way to move electricity. Perhaps ask him at this point why he thinks electric eels use this method to defend themselves. Hopefully he comes up with the answer tying this all together for him. Of course electric eels would use this way to defend themselves--electricity moves far and fast and can deter predators quickly with a jolt.

The ions are not "used up" per se. As he will learn soon enough energy (in this case energy - ions) can be moved and shared. Here is a perfect adult example. Your AA batteries. Two kinds of batteries, right? Rechargeable and non-rechargeable. Why is this? Here we go: Batteries each have a boatload of ions on one side. As you use the batteries the ions move from one side of this dividing line to the other in an attempt to balance (remember diffusion from science? This is diffusion. High concentration to low concentration. BTW this is what smell is. A scent in the air trying to go from superconcentrated to equalizing in the air so all of the air has the same amount). So--now that we know this. What the heck happens in rechargeable batteries? You are putting them after they are no longer working on a system that MOVES THE IONS BACK! Not lost, see? Just moved.

I am not sure if he would totally get this concept, so if you want to keep it super simple and say used up then I don't foresee a problem right now with that.

Hope this helps!

Elizabeth

mimi9000
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Re: Another lemon battery question

Postby mimi9000 » Wed Mar 30, 2016 11:10 pm

Hi Elizabeth,

Thanks for your reply! We did the deionized water/salt water experiment and that helped tremendously.

I also explained the concept of moving ions and my son seemed to understand it.

This experiment has been great fun and I learned a lot as well. Wish I'd had this forum when I was a student.

Thanks again!


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