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Spectrophotometry LAB
How is color measured?
Color is an important part of life and chemistry. Dyes are chemicals that create color by absorbing
light. If it seems odd that you can create color by taking away light, do this investigation and you
will be surprised! We will use a spectrophotometer to measure various colors. We will measure
the amount of red (R), blue (B) and green (G) colors absorbed by each colored solution.
Part 1 – Setting up the Lab-Master and Reference
1) Using a plastic pipette transfer water from a beaker to 3/4th in a clean cuvette.
2) Turn on the Lab Master by pressing the red/ green button at the bottom of the Lab Master.
3) Press “RGB ON” under Spectrophotometer.
4) Place the cuvette with water gently into the Lab-Master cuvette slot.
5) Press Reference twice.
6) Press Measure to get R, G and B reading for water and note the value in “clear” in Table 1.
7) Make sure that your observed value should be close to zero before you proceed to Part 2.
Part 2 – Measuring R, G and B for the colored solutions
1) Transfer 1 mL of one of the colored solutions from a beaker into another clean cuvette. Dilute
with water to 5 mL.
2) Place it in the Lab-Master and press measure.
3) Note down the R, G and B value in Table 1.
4) Rinse the cuvette with sufficient water and dispose the liquid into the waste beaker.
5) Repeat steps 1-4 using 2 and 3 mL of the same colored solution.
6) Repeat this for other colors.
Precautions:
1) Do not throw water or the colored solutions.
2) Wipe the cuvette before placing it in the Lab Master.
3) Do not press reference for colored solution. Press “Reference” only for water.
4) Use one color at one time.
5) After done with one color, pour it out into waste beaker before starting another color.
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Note: Replace “drop” with “mL”
Q) Make a graph showing how absorption changes with one, two, and three mL of food coloring.
You can plot all four colors on the same graph.