Science Buddies: "Ask an Expert"

Hello:
I have been doing this sciencebuddies experiment for my school science fair: https://www.sciencebuddies.org/science- ... on#summary.

I did the experiment on a few fabrics and at different temperatures, and I have the data. However, when I got to the section of analyzing the data, some steps confused me a little. The first one is step #2, which says: "Graph the average resistance of your three readings on the y-axis versus the concentration of the standard solutions in mg/mL on the x-axis."
Another one is step #5, which says: "Using your calibration curve, determine the concentration of Red 40 dye in each of your sample solutions (C0 and Ct). Remember to account for your dilution factor if a sample had to be diluted."
I an probably missing something, and I would really appreciate it if I could get a little assistance on how to do these steps.

Hello,

This sounds like a fun project! For Step #2 to "Graph the average resistance of your three readings on the y-axis versus the concentration of the standard solutions in mg/mL on the x-axis." use the resistance readings from steps #14-15 in the "Calibrating the Spectophotometer" section for the y-axis. For the x-axis you'll need to calculate the concentrations of your calibration or standard solutions. From step #4 in the "Calibrating the Spectophotometer" section we know that standard #1 is 0.12 mg/ml and each standard after that is a two-fold dilution so you can divide by two (standard #2 = 0.06 mg/ml, standard #3 = 0.03 mg/ml, etc). This part of the procedure was confusing and I had to spend quite a bit of time reading to understand!

For Step #5 "Using your calibration curve, determine the concentration of Red 40 dye in each of your sample solutions (C0 and Ct). Remember to account for your dilution factor if a sample had to be diluted." To do this you will need to add a trend line to the graph you created in Step #2 above. This equation is the calibration curve (Resistance = m * Concentation + b) and will allow you to determine the concentration mg/ml of your C0 and Ct based on the average resistance of these solutions. The comment around accounting for your dilution factor is related to step #8 in the "Starting and Monitoring the Dyeing Process" in case the resistance of your solution exceeds the maximum resistance of your calibration curve.

Hope this helps! Let us know if you have other questions.

Audrey