Gifted Issues Discussion homepage Forums General Discussion Science Fair experiment didn't work

So we screwed copper and zinc pieces into fruit and vegetables and then measured the results on a voltmeter. I have an 8 and 6 year old so wasn't going to get too complicated. The hypothesis was that the more acidic produce, like lemons and grapefruit, would make the best batteries and would read higher on the voltmeter. But that didn't happen. Everything read about 1, including the celery and avocado.
Do we just say that the hypothesis was incorrect according to our measurements, or do we need a reason. I don't understand why everything was reading 1, including a chunk of celery. So alkaline produce makes just as good of a battery as acidic? Does that make sense?

moomin, you do actually sound like an expert. We have a digital voltmeter somewhere but it is missing. So the celery and avocado were alkaline, but would they still oxidize the zinc electrode? I am panicking. We majorly procrastinated and the science fair is tonight. And I have to explain the experiment to the kids.

A couple of quick ways you could boost the voltage so it's measurable by your voltmeter:

1) Use magnesium in place of zinc.
2) Place electrodes in more than one piece of a given produce and wire them in series.

Ok, I looked at the celery and avocado again and they were slightly acidic as well (not according to the pH strips but values online). So basically all produce is acidic. I bought some giant mushrooms, so I will try those.

Dude--thanks, we will try that.

Congratulations, your experiment worked. Your hypothesis is false.

The mushroom was about .7.

I don't think the hypothesis is false, the zinc screw just isn't strong enough to show a difference between most things. I tried putting about 3 apples together and the voltage went up to about 2 but don't have enough produce to do that with everything.

Well, I guess that's why they do experiments, though I guess the theory might have something to say about it.

Well, it's done and on the poster board. I retested everything making sure the probes were about 2.5 inches apart. When my kids did it, some of them were about .5 inches apart. The celery and mushroom were both below 1, so at least the acidic fruit was higher. We put for the conclusion that the screw was probably not strong enough to produce more than 1 volt no matter how much acid is present, and more experiments are needed. Thanks for all the help! I was really lost, esp. since I thought there were actually some alkaline pieces of produce there based on the ph strips.

I'm glad it worked out for you. I feel your panic somewhat, because last year DD told us everything was under control (and in a Montessori school, we expect to be hands off unless told otherwise--given that the current teachers are awesome). As DH and I are both biologists by training, we were somewhat taken aback (okay, shocked and dismayed) when we found out that DD's "science experiment" last year consisted of mixing together maple syrup, corn syrup, and molasses and seeing what happened. REALLY?!?!?!! (I think she chose this based on a) knowing what would happen and b) being able to lick her fingers during the work
Fortunately the teacher was cool about it being a total waste of everyone's time, and we just apologized for not having realized what was going on, and vowing to help DD do an actual experiment this year. So we've already been brainstorming, and are determined to have DD actually do what is intended this year. However, we did notice last year at the presentation that there was a very evident and wide distribution of parent involvement--which IMO is fine in this school, since the emphasis is on learning what an experiment is and how to evaluate one.

Anyway, sorry you had to scramble at the last minute! But I'm glad it worked out. And I'm impressed that you were trying to help the kids figure it out and also get it to work correctly! Good for all of you

You apologized to the teacher because the teacher wasted everyone's time? I don't get it.

Perhaps they should have a declaration about the level of parent involvement, otherwise (if it is a contest, then) it is unfair to the kids who really do it themselves.

Okay, I'm totally confused. I guess I don't understand the concept of these Science Fairs. It seems that anything goes.