Electricity, Electrolytes, Confused Parent

[IgnoramusRex]

Hello,

I'm helping my son with his science fair project.

Our plan is to guess which of various substances will _______ electricity [this is my question] the best.

He will make a guess, explain it and then conduct the experiment (with close supervision).

Ammonia, vinegar, distilled water, lemon juice and a few substances will have zinc and copper nails dipped in them, with each hooked up to a voltmeter. After he records the voltage of each substance he will use pH strips and record those results. Hopefully there will be some sort of pattern and he (we) will learn something.

My questions so far:

Is he measuring "conductivity" here (in volts)?

Is a voltmeter the appropriate tool to use?

The science book from which he found a similar experiment seemed to indicate that conductivity is being measured, however when we Googled "conductivity" the unit of measure is siemens per meter, versus volts.

Thank you.

[calixte]

Hello!

This is a great question. Conductivity (as you said) is normally measured in siemens per meter (S/m), but the tool to use it (a conductivity meter) is not normally a household item. On the other hand you can use a multimeter set to measure resistance (ohms, Ω). A lower resistance means higher conductivity. Good luck!

[MadelineB]

If you are not familiar with a multimeter, Science Buddies to the rescue!

Here's a handy tutorial:

https://www.sciencebuddies.org/science- ... multimeter

Best of luck on this fun project!
Madeline

[IgnoramusRex]

Hello!

This is a great question. Conductivity (as you said) is normally measured in siemens per meter (S/m), but the tool to use it (a conductivity meter) is not normally a household item. On the other hand you can use a multimeter set to measure resistance (ohms, Ω). A lower resistance means higher conductivity. Good luck!

Thank you! I bought a basic conductivity meter (https://www.amazon.com/dp/B08R39SKXS?tag=pfamazon01-20
United Scientific™ CNDT01, Electric Conductivity Tester​) however the values were very similar except for the extreme pH ranges (1, 6-7, 13/14)--the meter only uses whole numbers 1-10, and I feel like the true picture of what is going on is a little hidden. We may try to measure ohms to see if those readings reveal more of a pattern.

Since we used the meter we dispensed with the copper/zinc. I think we may just use two copper wires to test ohms.

[amyCC]

I'm not sure what grade your student is in, but you might find this project helpful to look at. It's an advanced project, but I think the introduction and looking at how the measurements were done might be useful for you.

Electrolyte Challenge: https://www.sciencebuddies.org/science- ... orts-drink

Amy
Science Buddies

[bfinio]

Hi - chiming in because I think two related concepts are being mixed up here and there's a very important distinction.

Conductivity refers to a material's ability to conduct electricity. Some materials are conductors (most metals). Other materials are insulators (wood, plastic, rubber, etc). Within materials that are conductors, some are better conductors than others. You can do an experiment to measure this by connecting an external battery to a material and using a multimeter to measure the amount of current flowing. For a constant external voltage supplied by a battery, a more conductive material will let more current flow. (*don't worry about the units for now)

However, this is the important part - that is not what you are doing in the experiment you described. In your experiment you are using the liquids as the electrolyte in a battery. The zinc and copper nails are the electrodes of the battery. Voltage is generated due to a chemical reaction between the electrolyte and the electrodes, and you can connect a multimeter to measure this voltage, but that is not the same as asking "which of these liquids is a better conductor?" I'm not a chemist, so not great at explaining the electrochemical part of this, but our potato battery and salt water battery projects have more information about the chemistry in the background sections (note that both projects use copper and zinc electrodes):

https://www.sciencebuddies.org/science- ... to-battery

https://www.sciencebuddies.org/science- ... -saltwater

Those two projects offer a better description of what you are currently doing. Note how neither project has a separate, external battery - the thing you build is the battery, and you can measure its electrical output (current and/or voltage), which depends on different factors including the electrolyte and electrode materials as well as surface area.

If you want to switch to measuring how much current flows through the different liquids and which one is a better conductor, then the project Amy linked is the one you want: https://www.sciencebuddies.org/science- ... orts-drink. Note how that project has a separate, external battery that powers the circuit, and BOTH electrodes in the conductivity sensor are copper (instead of one copper, one zinc) - so you are measuring current through the liquid, but not using the liquid as the electrode in a battery.

Hope all of that helps clarify. I could write another entire post clearing up all the units but wanted to stop there for now.

[bfinio]

Oops - I wrote the above in reply to your original post, and missed the follow up about how you have ditched the copper/zinc electrodes and were trying to just measure conducitivity. I have never used a conductivity meter like the one you linked, so I'm not sure how sensitive they are. I would expect that you'd at least see lower conductivity for distilled water, but you may get similar results for the other liquids you mentioned. You can try googling the conductivities of those different liquids to see if your results line up with expected values.

[IgnoramusRex]

I'm not sure what grade your student is in, but you might find this project helpful to look at. It's an advanced project, but I think the introduction and looking at how the measurements were done might be useful for you.

Electrolyte Challenge: https://www.sciencebuddies.org/science- ... orts-drink

Amy
Science Buddies

Thank you! That's helpful

[IgnoramusRex]

Oops - I wrote the above in reply to your original post, and missed the follow up about how you have ditched the copper/zinc electrodes and were trying to just measure conducitivity. I have never used a conductivity meter like the one you linked, so I'm not sure how sensitive they are. I would expect that you'd at least see lower conductivity for distilled water, but you may get similar results for the other liquids you mentioned. You can try googling the conductivities of those different liquids to see if your results line up with expected values.

Thank you! We definitely had two concepts mixed together at the beginning. I think we may want to explore the battery idea later on, since we have lots of extra pH test strips and it seems like a fun idea.

Thankfully the meter works just well enough, I think, to illustrate the basic concept.