Investigation 1: What Is the Relationship Between the
Concentration of a Solution and the Amount of Light Transmitted Through the
Solution? (1/2 pt)
Lab Partners: (1/2 pt)
Challenge: (1 pt)
Measure the amount of blue dye in blue sports drink using light.
Introduction/Background: (DON’T write in your
lab book):
Measuring how much of different wavelengths of light are absorbed by a
substance, and getting useful information about the substance from the
results, is the scientific discipline of spectroscopy. The visible spectrum
is the only part of the electromagnetic spectrum that we can access with the
equipment found in a typical high school chemistry laboratory. The basic
principles of spectral analysis that you learn in high school can also be
applied to more sophisticated instrumentation required to access the
ultraviolet, infrared, and x-ray regions. What you learn by performing this
lab will help you understand more sophisticated instruments that you may
encounter in a college or
university. In a visible spectrophotometer, we shine a beam of light into a
solution containing the sample and detect how much of it comes out of the
other side of the solution. By comparing the amount of light transmitted by
the pure solvent to the amount transmitted when the sample is dissolved in
it, we can calculate a quantity called the absorbance. Spectrophotometers
can report measurements as percent transmittance (%T) or directly as
absorbance. In this investigation, you will be guided to discover the
relationship between transmittance and concentration and, ultimately, the
relationships among transmittance, absorbance, and concentration of
solution.
In this lab, you will be given a known concentration (“stock solution”) of
the blue #1 due (Brilliant Blue) molecule dissolved in water (see Figure 1).
The blue #1 dye molecule is the only chemical species in the solution. You
will be measuring the percent transmittance of light through a solution
containing only this chemical species.
Pre-Lab Questions: (answer in your lab book in
complete sentences) (3 pt)
1) How does a spectrophotometer/colorimeter work?
2) What is transmittance?
3) The spectrophotometer will be set at 635 nm for this experiment. What
color is light
with a wavelength of 635 nm? Is this the same color as the sports drink we
will use or
different?
4) What is the frequency of a photon of light with a wavelength of 635 nm?
5) What is the energy of one photon with a wavelength of 635 nm?
Pre-Lab Testing:
Materials – (DON’T list in your lab book):
5 cuvettes
Vernier Colorimeter
Vernier Go! Link
Chromebook with Graphical Analysis
droppers
10.0 ml graduated cylinder
distilled water
5.0 X 10-3 M stock solution of FD & C Blue #1 dye (0.404g of blue
dye/100ml of solution) Molar mass: 792.84 g/mol
Procedure -(DON’T list in your lab book):
1. Connect Go! Link to Chromebook and Colorimeter to Go! Link
2. Set the colorimeter to 635 nm.
3. Physically and chemically clean the five cuvettes
5. Make two of the following dilutions assigned to your group using the
dropper and 10 ml graduated cylinder:
10 mL stock/0 mL water 5 mL stock/5 mL water
9 mL stock/1 mL water 4 mL stock/6 mL water
8 mL stock/2 mL water 3 mL stock/7 mL water
7 mL stock/3 mL water 2 mL stock/8 mL water
6 mL stock/4 mL water 1 mL stock/9 mL water
7. Collect the absorbance values of your group’s assigned diluted
solutions using
the colorimeter.
8. Enter your group's data in the class data table.
9. Clean up.
Pre-lab testing questions (Answer in lab book and show work): (8
total pt)
1) Calculate the molar concentration of each of the diluted solutions you
tested using M1V1 = M2V2. (2
pts)
2) Copy class data table into your notebook (3 pts)
3) Make a graph of absorbance (y-axis) vs. molar concentration (x-axis).
(3 pts)
MSDS: (1 pt)
Look up Blue #1 dye
Procedure: (4 pt)
Write a detailed procedure to test the concentration and mass of
the blue dye in a Gatorade drink.
Include a drawing of the set-up
Data Table: (2 pt)
Create a data table to collect your data for three trials of the blue sports
drink
Analysis Questions:
(Answer in lab book and show work): (5 pt)
1) Calculate average absorbance for sports drink.
2) Calculate standard deviation for sports drink data.
3) Determine the molar concentration of blue #1 dye in the sports drink.
Show all work or highlight and label value on graph.
4) Determine the mass of blue #1 dye found in the drink. Show all work.
(Hint: See materials above for molar mass!)
5) Suppose a solution was too concentrated for an accurate reading with the
colorimeter. The concentrated solution was diluted by placing 1.00 mL of the
concentrated solution in 4.00 mL of water. The solution was then placed in
the
colorimeter and an absorbance was obtained. After a few calculations, the
molar
concentration was calculated to be 3.5 × 10–6 M. What was the
concentration of the
original stock solution before dilution?
Conclusion: (6 pt)
As usual using the blue lab format sheet
Lab handout based on the experiment “Investigation 1: What Is the
Relationship Between the
Concentration of a Solution and the Amount of Light Transmitted Through the
Solution?” in AP
Chemistry Guided-Inquiry Experiments: Applying the Science Practices
(College Board, 2013