How blue is your sports drink HELP!

[deleted-406640]

I am kinda confused with this project (How blue is your sports drink?) and need help with the relation of the resistance and the absorbance. Is the resistance showing up in the multimeter the sample's absorbance? Also, I cannot find the megohms in my multimeter (it came with the it that was recommended) for when I am measuring the resistance with the LED off, so I am not sure if I am getting inaccurate results. Overall, I am just not sure if the results I am getting are accurate, since the measurement of the resistance with only the blank substance and the orange absorption filter had a higher number than some pigmented substances.

[norman40]

Hi nicolarios,

I’m assuming that you’re working on the project described here:

https://www.sciencebuddies.org/science- ... ml#summary

In this project the amount of light passing through the various drink solutions is measured with a photoresistor. The resistance of the photoresistor increases when the amount of light passing through a solution decreases. If less light passes through then the absorption of the solution is higher. So the light absorption of the solution is directly proportional to the resistance of the photoresistor.

Your multimeter may have a 2000K ohms range setting. This is the same as 2 mega-ohms. If you have this setting or something similar, use it for the resistance measurement with the LED off.

Your resistance measurements for the blank (water only) and the orange filter should be lower than for any of the sports drink samples. The measurements are sensitive to the distance between the LED and the photoresistor (this is the path length discussed in the project background). When making the measurements take care to keep this distance constant. Also, it’s important to keep the alignment of the LED and photoresistor constant for your measurements.

I hope this helps. Please post again if you have more questions.

A. Norman

[deleted-406640]

Thanks! We did these previous step in the "How blue is your sports drink" project and figured it out, but now we are stuck on the analyzing your results part.

We calculated the average of every standard solution and sports drink. But in the calibration curve, we are not sure what we have to write. First it says to write the average resistance of the standard solutions on the y-axis and the concentration of the standard solutions on the x-axis. It then says that we have to graph the average resistance of the sports drinks on the graph. How and where do we graph the average resistance of our sports drinks? After that, how do we calculate the concentration by losing at the graph? Sorry for asking so much, I just want to have the most accurate results possible!
Thanks in advance.

[deleted-406640]

We are stuck in the analyzing results part of the "How blue is your sports drink" project.

We calculated the average of every standard solution and sports drink. But in the calibration curve, we are not sure what we have to write. First it says to write the average resistance of the standard solutions on the y-axis and the concentration of the standard solutions on the x-axis. It then says that we have to graph the average resistance of the sports drinks on the graph. How and where do we graph the average resistance of our sports drinks? After that, how do we calculate the concentration by losing at the graph? Sorry for asking so much, I just want to have the most accurate results possible!
Thanks in advance.

[norman40]

Hi nicolarios,

The purpose of the calibration curve is to show the relationship between the concentration of the blue dye and the absorbance (resistance) of the dye solution. Once you have this relationship you can use it to find the concentration of blue dye in “unknown” solutions like the sports drinks.

The calibration curve is a graph of the dye concentration on the x-axis and the resistance on the y-axis. Your calibration curve should be a straight line. The data analysis will be a little easier if you draw in a straight line though the calibration data. If you are using a spreadsheet, the software can add this line to your chart.

Use the resistance you measured for a sports drink sample by finding its resistance value on the y-axis of the calibration graph. Next, move along a horizontal line from the resistance value on the y-axis to the point where the horizontal line intersects the calibration curve. Now move along a vertical line to the x-axis. The intersection at the x-axis is the concentration for your sports drink sample.

After you have found concentrations of you sports drink samples, you can add these data to your graph if you like. Another suggestion is to make a bar chart to compare the concentrations of the different drinks.

I hope this helps. Please post again if you have more questions.

A. Norman

[deleted-406640]

I got it, thanks! But does the line HAVE to be straight? Because ours turned out a little wonky, even though it goes up.

[norman40]

Hi nicolarios,

You should draw in a straight line that is positioned so that your calibration data points are as close to the line as possible. It’s OK if some of your data lie above and below the line. Just try to draw in a line with the data evenly distributed around it. This is called a “best fit” line and it represents the average relationship between the independent variable (dye concentration) and the dependent variable (resistance).

Some more information on adding a “best fit” line to a graph is available at the following links:

http://serc.carleton.edu/mathyouneed/gr ... stfit.html

http://mathbits.com/MathBits/TISection/ ... ineFit.htm


I hope this helps. Please post again if you have more questions.

A. Norman