Analysing sports drinks electrolyte experiment data

Ask questions about projects relating to: biology, biochemistry, genomics, microbiology, molecular biology, pharmacology/toxicology, zoology, human behavior, archeology, anthropology, political science, sociology, geology, environmental science, oceanography, seismology, weather, or atmosphere.

Moderators: MelissaB, kgudger, Ray Trent, Moderators

Analysing sports drinks electrolyte experiment data

Postby joshuashjacoby » Sun Jun 03, 2012 5:50 pm

Hi
I have analysed the electrolyte content of a range of sports drinks bymeasuring the resistance of each using a multimeter, and then converting ohms to siemens by G=1/resistance. However, my data is in the exact opposite order to what I would have expected, apart from tap water, which had the lowest conductivity reading. The drink that marketed itself as having 50% more electrolytes than any other sports drink in fact scored the lowest; the one that said 33% more was the second lowest etc. What does this mean? I tested each drink 3 times using a fresh sample each time, and i rinsed the probes in distilled water and dried them between each test. I kept the probes in each drink for 15 seconds. Is there something I could have done to mess up my results, or have I shown that the advertsing is wrong?


My results are below
Reading 1 Reading 2 Reading 3 Average Ohms Average Siemens
Tap water 70.9 69.7 69.3 69.96666667 0.014
drink 1 (50% more) 7.96 8.44 7.87 8.09 0.124
drink 2 (33% more) 8.7 6.09 4.54 6.443333333 0.155
drink 3 6.02 5.8 6.69 6.17 0.162
drink 4 6.44 5.86 5.65 5.983333333 0.167
drink 5 5.84 4.95 5.75 5.513333333 0.181

Thanks for your help.
joshuashjacoby
 
Posts: 4
Joined: Sun Jun 03, 2012 5:38 pm
Occupation: Student 8 Grade
Project Question: Electrolytes in sports drinks
Project Due Date: 22 June
Project Status: I am finished with my experiment and analyzing the data

Re: Analysing sports drinks electrolyte experiment data

Postby rmarz » Sun Jun 03, 2012 6:35 pm

joshuashjacoby - I'm afraid there is something wrong with your test setup. Tap water would never measure a resistance as low as 70.9 Ω. You said you were reading resistance, not current flow with the multimeter. This experiment usually is set up using a 9 volt battery in series with the test solution and a multimeter. I just took a digital multimeter and put the probes into a small cup of tap water. It measured about 1.4 meg Ω before some electrolysis occurred on the leads and the resistance started increasing. So you are many magnitudes away from a correct reading. Can you send us a description of your setup, the ranges you used on the multimeter, and whether or not you were using an external battery and actually measuring DC current as opposed to using the ohmmeter scales and settings. We'll help you get to the right answers.

Rick Marz
rmarz
Expert
 
Posts: 451
Joined: Sat Oct 25, 2008 1:26 pm
Occupation: Technology Consultant
Project Question: n/a
Project Due Date: n/a
Project Status: Not applicable

Re: Analysing sports drinks electrolyte experiment data

Postby joshuashjacoby » Sun Jun 03, 2012 10:22 pm

Hi Rick
When we used the original setup measuring current using a 9v battery in series we got no readings at all on 2 multimeters. A science teacher then said we could just use the resistance setting on the multimeter and invert the result, but the results are weird.

When we did the resistance readings, we used a multimeter set to Ω. It doesn't have any other ranges. We just inserted the probes into the water straight from the meter, not using an external battery. We timed each reading at 15 seconds to allow for the same amount of electrolysis in each sample.

I've just tried another meter with a range of ohm settings. On the 2M setting I get a reading of 0.415 for distilled water. If I use any other setting on the meter I get a reading of 1. I'm not sure what this means!

Thanks
joshuashjacoby
 
Posts: 4
Joined: Sun Jun 03, 2012 5:38 pm
Occupation: Student 8 Grade
Project Question: Electrolytes in sports drinks
Project Due Date: 22 June
Project Status: I am finished with my experiment and analyzing the data

Re: Analysing sports drinks electrolyte experiment data

Postby rmarz » Mon Jun 04, 2012 7:39 am

joshuashjacoby - To explain a few things you just mentioned. Your reading of 0.415 on the 2 MΩ scale is interpreted as 415 KΩ. A better start. When you just see a '1' on the display, and a decimal to the far right, with no other digits, the value is 'out of range' and another range should be selected. Typically in the more ionized electrolytes, you may be required to use the 2 KΩ range on the meter. You might typically see values that range from less than 100 Ω to several thousand Ω's in your test solutions. These would be consistent with expected results and can be converted into siemen units. The original meter you used didn't seem capable of these high value readings. An inexpensive digital multimeter can be used in this experiment. One caution, do not leave the probes in the solution too long. Your earliest reading (a second or so) will be your best. A slight amount of electrolytic action will start and produce micro-bubles of hydrogen and oxygen on the probes and create errors in your readings. Consistency in measurement technique helps here as well. Your process of cleaning the probes in distilled water and drying them between measurements is also a good practice.

Rick Marz
rmarz
Expert
 
Posts: 451
Joined: Sat Oct 25, 2008 1:26 pm
Occupation: Technology Consultant
Project Question: n/a
Project Due Date: n/a
Project Status: Not applicable

Re: Analysing sports drinks electrolyte experiment data

Postby joshuashjacoby » Mon Jun 04, 2012 2:13 pm

Hi
Thanks very much for the help. I'll redo the readings using the immediate reading rather than waiting 15 seconds.
joshuashjacoby
 
Posts: 4
Joined: Sun Jun 03, 2012 5:38 pm
Occupation: Student 8 Grade
Project Question: Electrolytes in sports drinks
Project Due Date: 22 June
Project Status: I am finished with my experiment and analyzing the data

Re: Analysing sports drinks electrolyte experiment data

Postby joshuashjacoby » Fri Jun 08, 2012 2:11 pm

Hello
Thanks for your help - the readings make more sense now. I was just wondering though, is the reason you use the copper wire and battery and test current rather than resistance to avoid the problem of electrolysis?
J
joshuashjacoby
 
Posts: 4
Joined: Sun Jun 03, 2012 5:38 pm
Occupation: Student 8 Grade
Project Question: Electrolytes in sports drinks
Project Due Date: 22 June
Project Status: I am finished with my experiment and analyzing the data

Re: Analysing sports drinks electrolyte experiment data

Postby rmarz » Fri Jun 08, 2012 6:07 pm

joshuajacoby - You raise an interesting question about this experiment. In the past, I have sampled some juices and beverages as well as tap and distilled water using the 9V battery and ammeter procedure. Obviously the water represents a very high resistance (low conductivity) liquid. Using the 9V battery and measuring current, values were very low, in the order of microamps. The high conductance drinks measured between 40 and 100 milliamps, a very high current. Electrolysis is a greater factor in the high current measurements. When using a digital multimeter in the ohmmeter ranges, the measured currents in the loop are very low, just over 1 milliamp on the 200 Ω range and going even lower on the high ohm ranges like 20KΩ and 200KΩ, as low as a few 10's of microamps on the other scales. This suggests that the electrolysis error is actually minimal when using the ohmmeter compared to the 9V battery and ammeter. As you know, the way the ohmmeter works is to use an internal battery as a current source, often a 9V battery to measure resistance, but clearly in a much higher resistance loop. This may introduce some errors over several measurement ranges, but reduce other errors at the same time.

I will suggest to the team to consider correlating the results of the two procedures and documenting it in any future revision of this experiment. There are no doubt some trade-offs and non-linearity issues when dealing with measurements over several magnitudes of values, but that is one of the reasons we call them experiments. We're not quite invoking Heisenberg's Principle, but we are dealing with some measurement interactions.

Rick Marz
rmarz
Expert
 
Posts: 451
Joined: Sat Oct 25, 2008 1:26 pm
Occupation: Technology Consultant
Project Question: n/a
Project Due Date: n/a
Project Status: Not applicable


Return to Grades 6-8: Life, Earth, and Social Sciences

Who is online

Users browsing this forum: No registered users and 4 guests