Science Buddies: "Ask an Expert"

For the experiment,
I got an average reading of 42.6 microamps for Gatorade
47.1 microamps for orange juice
8.63 microamps for tap water
and 0 microamps for distilled water
and then for the microamps to siemens conversions, I got
4.72 microsiemens for Gatorade
5.23 microsiemens for Orange Juice
0.959 microsiemens for Tap Water
and 0 microsiemens for distilled water
I am wondering if these results are within the correct range for the experiment, and if I did my microamps to siemens and siemens to microsiemens conversions correctly. The multimeter that I used to get the data was the Equus 3320 Auto-Ranging Digital Multimeter as the link guides to on the website. I am also wondeirng if these results are expected from the Equus 3320 Auto-Ranging Digital Multimeter that I used for my experiment. I am very confused on the accuracy of these results, because I had a lot of trouble and confusion on building the conductance sensor.

Chemlab,

Welcome and thank you for your questions. You should get current measurements close to zero for distilled water, but somewhere between 30 and 100 milliamps in some of the drinks. Your readings seem to be about 3 orders of magnitude low. Set your multimeter to the 200 milliamps range, or make sure you aren't mistaking microamps for milliamps. Remember, digital multimeters read back in the range setting they are in. For example, a reading of 1.0 in the 200 milliamp setting is 1.0 milliamps, which equals 0.001 amps (or 1000 microamps). Also, you should get in the range of 2.0 millisiemens for OJ and Sports drink.

Suggestions: Double check your circuit for proper configuration, ensure your multimeter is on the right amp range setting, ensure you use a reasonablely fresh 9V battery for all the tests.

For additional accuracy, if you have access to a second multimeter, you could also measure the DC voltage across the electrodes inserted into the drink specimen and use that value in your calculations instead of just assuming 9V.

As a side note for this type of experiment, there seems to be a relationship between conductivity and temperature of the drink specimen. For even more accuracy, you might consider making sure all your testing fluids are at the same temperature at time of testing as an additional control variable.

Could it be possible that I used the wrong units, and all of the microamps and microsiemens are actually milliamps and millisiemens. Would that make my data correct?

Gatorade-1.61 millisiemens
Orange Juice-2.06 millisiemens
Tap water- 0.57 millisiemens
Distilled water- 0 millisiemens
I redid the experiment, but I don't know whether these new results are good or not. A fuse may have broke or something. Please tell me if these results are within correct range.

I looks like you are in the right range now. A key component of any scientific experiment is repeatability. I suggest running the experiment at least 2 more times under the same test setup and conditions with new drink samples and see if you get similar results. If they are close, say +/- 5%, then you can take the average of the readings for each sample and report that value as the result. You can also take it a step further and report a sensitivity range. For example, if you measured 3 samples of OJ and came up with 2.00, 2.06, 2.03 millisiemens then your average is 2.03mS +/- 1.5%.

Thank you so much!!!