Science Buddies: "Ask an Expert"

Hi, I'm doing the Electrolyte Challenge using Gatorade, Coconut water, and Pickle juice and trying to find which one hsa the most electrolytes. I tried finding my conductance but I got answers like .00002 and .000032 so I'm pretty sure I'm doiing something wrong and I'm hoping you could help ASAP! My project is suppossed to be completed my tomorrow but I still have another weekend until I actually have to trun in my graphs, data tables, and conclusion so, if needed, I have a little more time. I used 1/2 of each solution. On the multimeter I set the setting to 20mA under the DCA section and got various answers such as .26, .17, .32, etc. Then when I converted the milliamps to amps I got answers like .0002, .00029, and .00016. Then I divided these numbers by 9 (to get the conductance) and got even smaller answers like .00002, .000032, and .000018. PLEASE HELP ME SOON!!!!!!

Hello and welcome to the forum!

I noticed this project uses a 9V battery to measure the conductance of the liquids. This may be a problem, so I will contact ScienceBuddies staff about this. To make sure the 9V battery is not causing you problems, can you please measure the Voltage of the 9V battery now? If your experiments have exhausted the battery, we need to know it. If it still reads 9V, then you are in good shape.

I haven't done this experiment, but your numbers may be correct. The experiment looks at relative conductance, so the absolute numbers are not as important. From your numbers you may want to report the conductance in micro siemens. Your numbers become 20, 32 and 18 microsiemens, which seem different enough to satisfy the experimental goals. (To turn Siemens into microsiemens, multiply by 1,000,000.)

If you could check your battery voltage and consider the above ideas, please let us know how it turns out. Thanks!
Keith

Ok thanks so much! I will measure the voltage, but how exactly am I suppossed to do that?

Hi:

Use your voltmeter on the "Voltage" scale (at least a 10V scale) and connect the battery's positive terminal (+) to the red voltmeter lead and connect the battery's negative (-) terminal to the black lead. A good battery will read more than 9V, a bad one less than 8V.

Keith

Ok I measured the voltage and it said 8.97 so I'm not sure exactly how good it is then. And also, so you think I should just turn my results into micro seimens so it will come up a bigger number? But overall, do you think that the results seem acceptable?

Your raw numbers seem reasonable to me in terms of they are well within the accuracy range of your measuring equipment and power source. 170 to 260 uA of current flow could easily be appropriate.

Now for the condutivity conversions. What did you use for contacts? (material, shape, exposed to liquid surface area) Were both electrodes the same material, shape, exposed liquid surface area? If not identical in all respects, you have a problem well beyond your grade level. How far apart were the electrodes? If the electrodes were farther appart than the smallest exposed dimension oriented toward the opposite electrode, again, you have a problem well beyond your grade level.

Absolute conductivity is typically a measurement of average current density in a volume of material. I don't see where any of your calculations are taking into account the dimensions of the volume of liquid where the current is flowing. In order for anybody to determine if your numbers agree with actual ion concentrations in the various liquids, the numbers have to absolute and not relative.

A cross check on whether your setup stayed accurate enough would have required you to measure the open circuit of your battery before and after you did this experiment. If the open circuit voltage changed significantly between the start and the end, then your setup changed enough to skew your results.