Concentration, Molarity, Absorbance, Transmittance

This week in class we focused on the concept of concentration and using Molarity.We learned that Molarity is the moles of a solute divided by L of the solution.

We also talked about absorbance and transmittance and how they are related to concentration. We talked about how Beer's Law relates absorbance to concentration: A=KC where A is the absorbance and K is the constant of 130,000 M^-1 cm^-1 and C is the concentration. We learned through our experiment that the more concentrated a solution is the less transmittance it will have.

 To do some more investigation about concentration, we did a lab with Blue #1 dye. In this lab we learned how to dilute a stock solution of Blue #1 by mixing together a certain number of milliliters of the stock solution with a certain number of milliliters of water. 

 For example  my group did 6/4 would mean 6mL of the stock solution and 4 mL of water and 1/9. 

Here is the link to the Blue #1 Lab Procedure which will detail more information about the lab and post lab questions.

Blue #1 Lab

We then learned how to operate a colorimeter, which is a device that sends a certain wavelength of light into the liquid to measure its absorbance. The dye that we were using is blue because the solution is allowing the blue light to pass through it. In order to measure the absorbance we used the wavelength of red light (635nm) because red is the furthest away from blue on the visible spectrum of light.

We placed the dilutions of the stock solution, and the gatorade and powerade into the colorimeter to figure out the absorbance of each of the solutions. From the stock solution we were able to as a class make a calibration curve for absorbance vs. concentration.

By using the equation provided by the calibration curve we were able to figure out the concentration of Blue #1 in the powerade and gatorade.

We figured out that the concentration of blue #1 in gatorade is 1.1 micromolar and the concentration in the powerade was2.8 micromolar.

From here we were able to use dimensional analysis to determine the concentrations of Blue #1 that would be in 500 mL of each drink.

Over all I think that this lab helped me to gain a better understanding of the relationship between molar concentration and absorbance. I liked being able to take one reading from the colorimeter and then being able to use that number to figure out absorbance and then from that number to figure out concentration. I like when we are forced to work through things on our own because I feel like I learn better when this happens. In particular when we had to do calculations on our own at home I really liked that.

I feel that I would give my understanding of the material a 7.5/10. This is because I feel that I understand the major concepts but I'm still having problems setting up problems that deal with this content. The last 3 questions on the lab made me think very hard and I had a difficult time figuring out what equation to use for question 1 (see Blue #1 lab under post lab assessments), even though it was an M1V1=M2V2. My group also had a hard time figuring out the grams of Blue #1 in  500 mL of the two drinks.  It was just hard to piece the calculations together with the information we were given. I feel that this is something that I need to work on, so that I can get to the point where I can do these types of problems with ease.

I'm now curious if the concentration of  different colored dye in other types of  gatorade and powerade  is the same as or different as the concentration of Blue #1 in the gatorade or powerade.