Science Buddies: "Ask an Expert"

I am trying to test the difference between electrolytes in sport drinks and water. I found my project on Science Buddies, BUT I am having trouble figuring out how to use the multimeter. I'm using a digital one as suggested, but the instructions numbered 1 - 9 are different then the picture example given on page 3. Which setting am I suppose to use AND what happens to the black/negative lead from the 9V battery? Doesn't it need to be attached to something? I know it's an open circuit but even though I submerge the conductance sensor in the liquids I get no reading on the Ma/A setting. If I connect all leads as it says in the picture (fig 2), I get a reading that goes up and down but never constant and my liquid starts to bubble around my copper wire. My mom doesn't know much about this kind of stuff and my step dad is in afganistan so I don't know who to ask these questions. PLEASE HELP. It took foreve to find 24gauge bare copper wire and now I'm running out of time and really dont' understand what I'm doing wrong.
Thank you!
Kodiak

Kodiak - I read through the description of the experiment entitled - Electrolyte Challenge: Orange Juice vs. Sports Drink - and understand some of your confusion. The schematic shown on figure 2 seems to be the clearest description of what you are attempting to do. Th 9V battery in series with your conductance probe in series with the DC multimeter will give you a conductance measurement on the multimeter. I don't understand the comments about avoiding the AC current range, as these multimeter's only read DC current. I also feel bad that you had to search for #24 bare copper wire. Almost any gauge bare copper wire would have worked fine. The problem you see as 'bubbling' around the electrodes is electrolysis, the breaking down of water molecules into oxygen and hydrogen by passing a DC current through the electrodes. I think some of the highly ionized sports drinks are so conductive that they are passing a relatively high current through the drink and causing electrolysis around the copper wires. You are actually 'bubbling' oxygen and hydrogen gas off the electrodes.

To minimize the electrolysis effect, your measurement must be made quickly before the surface area of the electrode is diminished by collecting the gas on it's surface. That is probably the reason for your changing measured values. They start out higher at first then go lower. Before testing the next sample, clean the electrode in water and dry. I would almost recommend doing this experiment at lower voltages, perhaps with a 1.5V battery, if electrolysis is a problem. Your results would still reflect the relative conductance in your samples. I hope this helps, good luck in continuing your experiment.

https://www.sciencebuddies.org/science- ... p053.shtml

Rick Marz

Kodiak, how far are your readings going up and down? In an experiment such as this, it will be almost impossible to get an entirely stable reading, minor fluctuations of the observed conductance are normal.