Science Buddies: "Ask an Expert"

I am doing one of the projects listed on your site called Electrolyte Challenge: Sports Drink VS. Orange Juice and I was wondering why we have to test the conductance of the tap water and the distilled water before actually getting to test the orange juice and sports drink because I tested the tap water and now that i've done the math and such , tap water seems to have the highest conductance. i just need to know why i need to test the tap water && distilled water basically ? and why just one trial and not three ?
-- Demi

Hi,

I think you are doing this project:

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

The conductivity reflects the concentration of electrolytes like sodium and chloride ions in the sample. Tap water should have a very low conductivity and sports drinks and orange juice will have a high conductivity. The concentration of sodium chloride in humans is about 150 mM and this project suggests testing the conductivity of various drinks, but you could pick different samples to test. You need to test tap/distilled water to determine the lowest reading or zero point for your conductivity measurement. This will help verify your meter is working properly.

Something is wrong with your conductance meter and you need to do some troubleshooting. Here are some questions that might help determine what’s wrong with your meter/sample:

1. Are you using softened water for tap water?

2. Do you have a conductivity standard to try? Or, if you add some table salt to your tap water, does the conductivity increase?

3. Try testing the conductivity of deionized water or distilled water. This should give you a low reading.

4. What units are your results in?

5. Please post your samples and results.


In addition to the information from the Science Buddies project site, here is a commercial website that contains some good information about conductivity testing.

http://www.eutechinst.com/techtips/tech-tips25.htm
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Do you have any questions at this point?

Donna Hardy

Oh okay ! Thank you ! Now I understand. I appreciate you time ! thanksss (:
--Demi

what were your results ?

Hello, I am a teacher wondering what the average results would be in Milli Amps for both orange juice and a sports drink? I would like to compare this sites results to my students. Please respond as soon as possible, I would like to cross examine tonight

Thanks,
Declan

DeclanCoulson wrote:I am a teacher wondering what the average results would be in Milli Amps

I'm about to offend you. If you actually understood this experiment, you would know that the electrical current flow measured with any particular current probe apparatus is not independent of the geometry of the probe. Both the measured current and probe geometry are needed to calculate a electrolytic conductivity in standardized scientific units of siemens / meter.

Gemoetry Simplification:
The calculations described in this experimental proceedure only uses the distance between the wound contacts and ignores the any effects caused by the solution displaced by the rod. The difference between this simplification and probe geometries that displace less liquid in the highest current flow density areas isn't important for the expected siemens/M range in this experiment (significant differences will only occur at very high and very low elecrolytic conductivities).

For any given (elecrolytic conductance) liquid,
1) If you double the length of the electrode spacing, you will halve the electrical current, or
2) If you halve the length of the electrode spacing, you will double the electrical current.