Science Buddies: "Ask an Expert"

Hi, I'm doing the electrolyte challenge using OJ, lemonade flavored Gatorade, distiller water, and tap water. I've looked at other results and they don't look anything like mine. My results from my multimeter (which is a Innova 3300) were: distiller water 0.00; tap water 0.00; Gatorade 0.02; OJ 0.05. I haven't done the conductance formula yet. When I measured my electrolytes. I tested it under the DC10A setting. What does the 10A mean? Is it already in amps or do I have to convert it to amps? Also for the conductance formula (conductance=current/voltage), what would the voltage be if I was using a 9v battery? Lastly, is my data specific enough because others got it down to 0.025 and stuff. Please help! My data is due by 12/22/11.

I just posted this in another topic under Electrolytes, but I didn't know if I was supposed to make a new topic (sorry new to this ). Hi, I'm doing the electrolyte challenge using OJ, lemonade flavored Gatorade, distiller water, and tap water. I've looked at other results and they don't look anything like mine. My results from my multimeter (which is a Innova 3300) were: distiller water 0.00; tap water 0.00; Gatorade 0.02; OJ 0.05. I haven't done the conductance formula yet. When I measured my electrolytes. I tested it under the DC10A setting. What does the 10A mean? Is it already in amps or do I have to convert it to amps? Also for the conductance formula (conductance=current/voltage), what would the voltage be if I was using a 9v battery? Lastly, is my data specific enough because others got it down to 0.025 and stuff. Please help! My data is due by 12/22/11.

rubberducky1276 - In this experiment will measure current values from zero to just a few microamps for distilled water, and upwards of 30-100 milliamps in some of the drinks being tested. Your use of the 10 Amp range is inconsistent with the levels of current being measured. I assume you have used the special 10 Amp socket for your black probe. Change your black (negative) probe to the COM (center socket on this multimeter) and leave the red (positive) probe in the V Ω mA socket. Then set your range to 200 milliamps for the measurements. It's possible that the distilled water may show a zero reading on this scale, so you can change your range to a much lower level. Because it is a digital multimeter, the reading you get will be in whole units of the scale setting. In the 200 milliamp range, a reading of 20.9 is 20.9 milliamps.

To do your conductivity calculations, assuming a reasonably fresh 9 volt battery: on the lower current ranges you can probably assume that the full 9 volts for your calculation. If you are drawing something like 100 milliamps, there might be a slight reduction in voltage due to internal resistance of the battery at the higher current drain. To be very precise, if you have access to a second multimeter, you could monitor the actual DC voltage across the electrodes that are inserted into the electrolyte. Use that value in your conductance calculation.

Rick Marz

See answer in duplicate posting. https://www.sciencebuddies.org/science- ... =26&t=8611

WW

wendellwiggins wrote:See answer in duplicate posting. https://www.sciencebuddies.org/science- ... =26&t=8611

WW

I kept clicking on the link but nothing happened

Rick Marz,
I changed my red probe to the V Ω mA socket and then black probe I left in COM. I set my range to the 200 milliamps setting under DCA but nothing happened for any of the fluids. Then I changed it to 20 then the lowest, but still, nothing happened. I redid my conductance sensor and replaced the 9v battery with a new one. I don't know why I'm not getting any results. The wires aren't touching and everything is connected. Am I supposed to measure the electrolytes under DCA or DCV? I'm really confused and my teacher doesn't know what to do. Please help!

rubberducky1276 - If all your connections are correct, and your battery is new, you should definitely get some reading on the 200 ma DCA scale with a sports drink or orange juice. If you have access to a 1,000 ohm resistor, connect it to your two electrodes in place of the electrolyte. You should read about 9 ma. Is your sensor using bare copper wire? Do other functions on your multimeter work? Can you read 9 volts DC on the 20 volt VDC scale. If you have the 1,000 ohm resistor, does the ohmmeter read the proper value? These tests are just trying to resolve that your meter is functioning. The circuit is very simple. The battery is connected in series with the multimeter and is in series with the electrolyte under test.

Rick Marz

I realized that my fuse on multimeter broke. After retesting with a new fuse, I got:
Distilled Water-0.0
Tap Water-2.1
Gatorade-22.1
Orange Juice-48.2
These results still don't seem right though. I don't know. I am using bare copper wire. I measured it under 200m on DCA. I haven't done my conductance calculations yet too. Sorry for the trouble.

rubberducky1276 - Congratulations! These measurements seem to be in the range I would expect in this experiment. I believe you can do your conductance calculations with these results.

Rick Marz

For my science fair experiment, I am doing the Electrolyte Challenge with a 9volt battery - measuring milliamps and calculating conductance using the formula G=I/V where G is siemens, I is amps and V is volts. I am testing Gatorade, Powerade, Propel, Apple Juice, Grape Juice, and Orange Juice, with three trials for each liquid. For Gatorade, I had an average of 0.0196 milliamps (.0000196 amps), and a conductance of 0.00000217 siemens. For Powerade, I had an average of 0.0203 milliamps, and a conductance of 0.0000018922 siemens. For Propel, I had an average of 0.013 milliamps, and a conductance of 0.0000014 siemens. For Apple Juice, I had an average of 0.011 milliamps, and a conductance of 0.0000012 siemens. For Grape Juice, I had an average of 0.0133 milliamps, and a conductance of 0.00000114 siemens. For Orange Juice, I had an average of 0.025 milliamps, and a conductance of 0.00000227 siemens.
Questions:
1) Are these results reasonable for this experiment?
2) Should I report the conductance in micro-siemans i.e. 2.17 micro-siemens vs. 0.00000217 siemens?

DJ Cha-Z - Your readings seem to be 3 orders of magnitude off. I think this is a problem of which scale on the multimeter you are using and possibly your interpretation of the values. For this experiment the meter is usually set to the 200 milliamps scale. Readings on the digital readout are in milliamps. For distilled or tap water, a more sensitive range like 20 microamps might be suitable. Otherwise the kinds of values you are seeing look appropriate. I would a suggest that your reading for Gatorade might be 19.6 milliamps, not 0.0196 milliamps. These will obviously significantly impact your conductance calculations.

Rick Marz

If we do the calculation using 19.6 milliamps or 0.0196 amps divided by 9 volts equals 0.00217 siemens. Does this look right, and if so, should we report that as 0.00217 siemens or 2.17mS (milli-siemens)? Which is considered the proper notation?

DJ Cha-Z - I think it is important to trace your steps to understand the readings you were getting, and the correct setup of the multimeter. Once you have verified that you have the correct readings then finalize your conductance calculations. For ease in understanding, I think it correct that you use whole numbers in expressing your results, thus the form of 2.17 millisiemens would be appropriate.

Rick Marz

My numbers were way off because I realized that my fuse on my multimeter broke. After retesting with a new fuse, I got the following results:

Gatorade-1.61 millisiemens
Powerade-0.73 millisiemens
Propel-0.76 millisiemens
Apple Juice-1.16 millisiemens
Grape Juice-1.31 millisiemens
Orange Juice-2.06 millisiemens

Are these results accurate?

DJ Cha-Z,

Your results seem reasonable now. Be sure to check pure water to be sure you get a low reading with it.

WW