Science Buddies: "Ask an Expert"

Hello, I am doing a project called “Electrolyte Challenge: Orange Juice vs. Sports Drink” and I have three questions on it:

1)Is it possible for you to explain how to make a simple conductance sensor better because when I was reading the guide lines to making the sensor it didn’t make sense?

2)How come you have to dip the sensor into distilled water 3 times after you immerse the sensor into the orange juice or sports drink???

3)Lastly, do you have to change the distilled water after you wash the sensor in it.

I hope you can help me and thank you very much for your advice!!!

Hi J.O.L.T88,

I hope I can help you out with some of your questions. For the first one, I thought that maybe rephrasing the directions for simple conductance sensor because sometimes that can be helpful. So I'm taking the directions from https://www.sciencebuddies.org/science- ... p053.shtml.
1. cut two pieces of copper wire (6 inches long)
2. cut a one inch piece of plastic tubing
3. On one end of the plastic tubing wrap one piece of copper wire several times around the tube (like you are winding a yo-yo or something). Leave about 2 inches unwound because you will need to connect it to the battery.
4. Do step 3 again on the other side of the plastic tube and make sure the two pieces of copper wire don't touch.
5. Connect your battery to the battery clip... the battery clip should fit over the end of the battery and have two wires coming out, usually a red one and a black one
6. So here's probably part of the problem. The picture that is on the website isn't the same as the directions so let me see if I can explain it better. Take one of the copper wires and attach an alligator clip to it. The other end of the alligator clip should be connected to the positive terminal of the battery (this should be the red wire or have a positive symbol on the end of the battery). Attach the other copper wire to an alligator clip and then attach the other end to the black terminal on the multimeter. Take another alligator clip and attach it to the other wire on the battery clip and then attach it to the red terminal on the multimeter. So now you should have a closed circuit. It should look similar to figure 2 in the directions... just don't pay attention to the positive and negative signs. There is additional information on the forum that talks about problems that other people have had with this step. If you want to look at those responses just type in "electrolyte challenge" in the search engine at the top of the page.

For your other questions...you dip your sensor in distilled water three times before changing from OJ to sports drink because you want to get all of the ions off of your sensor. So the ions that are present in the solutions cause the conductivity of the solution. After you take the sensor out of the solution there will still be some ions stuck on the surface. If you wash it in distilled water then it washes away all of the ions and when you dip them in the other solution you won't contaminate it. You wash it three times because when you wash you only get about 90% of the ions off with one wash, so you can be pretty sure that you will get almost all of it off if you wash three times. So to make sure your experiment is more accurate, I would change your distilled water after you wash your sensor.

Hope this is helpful

tzforbes

Thank you very much!!!! This explanation was so much easier to understand!!! The only problem i have now is buying another fuse for my multimeter because i let the positive and negative sides of the conductance sensor meet!!!

Thanks a bunch,

J.O.L.T88

Hello, I am doing a project called “Electrolyte Challenge: Orange Juice vs. Sports Drink” and I have three questions on it:

1)Is it possible for you to explain how to make a simple conductance sensor better because when I was reading the guide lines to making the sensor it didn’t make sense?

2)How come you have to dip the sensor into distilled water 3 times after you immerse the sensor into the orange juice or sports drink???

3)Lastly, do you have to change the distilled water after you wash the sensor in it.

4)how many alligator wires do i need?

I hope you can help me and thank you very much for your advice!!! [/quote]

angie panda wrote:2)How come you have to dip the sensor into distilled water 3 times after you immerse the sensor into the orange juice or sports drink???

Sports drinks and Orange juice have salts and acids in them (in other words electrolytes that ionize). If you fail to rinse them off the probe, you will contaminate the next test with carry over from the previous test. This is a similar question to why did your mother tell you to always wash your hands after going to the bathroom or playing in the dirt, contamination!

angie panda wrote:3)Lastly, do you have to change the distilled water after you wash the sensor in it.

Maybe. This is a question of dillution. If you dried off the probe on a clean piece of paper towel, then you imerse it into the first container of distilled water, then the amount of carry over is small. When you then dry it off on another clean piece of paper towel, and then dip it into the second container of distilled water, there will be even less carry over. When you then dry it off on another piece of paper towel, and imerse it in the third container, there shouldn't be much carry over left. Each time you repeat this process, the potential carry over gets diluted. Back when people washed dishes by hand in the sink, you could visually detect the soap carry over into the rinse water and determine when you wanted to change it.

angie panda wrote:4)how many alligator wires do i need?

Enough to complete the circuit reliably. If your meter test leads have clips on them already, then the only connection that an alligator clip might be useful for is between the battery and one of the conductance probes. If your meter test leads do not have clips or the clips aren't appropriate for the wire diameter you are using, then 3 might be useful.

Do I have to use alligator clips with rubber coverings or just plastic?

sciencewiz wrote:Do I have to use alligator clips with rubber coverings or just plastic?

The voltages and current levels in this experiment do not require insulated alligator clips for any safety purpose.

Rubber, plastic, bare metal makes no difference as long as the connections aren't touching each other and aren't immersed in the liquid.

The rubber and plastic sleeves aren't water tight so you can't make connections in the liquid without affecting the experiment to some extent.