Name: ______Block: ______Date: ______

LCPS Core Experience | Light Investigation ONE

Hold up a piece of white paper and then a piece of black paper to the light and look through them. Observe the differences that you see looking through the two papers.

  1. Which one lets the most light through? Black or White
  2. The least? Black or White
  1. Which color absorbs the most light? Black or White
  1. Which color transmits the most light? Black or White

Light Investigation ONE

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LCPS Core Experience | Light Investigation ONE

Lesson One: Observing the Relationship Between Absorption and Transmission of Light

  1. Look at the table and make predictions. Which solution will transmit more light and which will absorb more light?

Table A: Light Transmittance Through Colored Solutions

Beaker / Transmits
the Most Light / Absorbs the Most Light
A / CONTROL
B
C
D

Question: Explain the reasons for your predictions.

______

  1. Stand the flashlight upright on the table. Turn on the flashlight (the light should shine toward the ceiling). Turn off the overhead lights.
  1. Place Beaker A on top of the flashlight.
  1. Hold each steady to avoid spilling.
  2. Observe the amount of light transmitted through the beaker and on to the ceiling.
  1. Repeat with beakers B, C, and D by following steps 3 a – b for each beaker.
  1. Record: Use a checkmark to record your observations in Table B.

Table B: Light Transmittance Through Colored Solutions

Beaker / Transmits the Most Light / Absorbs the Most Light
A / CONTROL
B
C
D

Question: How does the shade of the water affect how much light is transmitted and absorbed in each beaker?

There appears to be a ______relationship between the shade of the solutions and the transmittance of light. The ______the shade of the solution, the______light transmitted. The______the shade of the solution, the_____light transmitted.

  1. Watch the teacher demonstrate how to use the spectrophotometer to measure absorbance and transmittance of light.
  1. Go back to your assigned spectrophotometer station. Follow the spectrophotometer directions to complete the lab. Record your results in Table C.

Table C: The Effect of Food Coloring Concentration on Light Transmittance and Absorbance

Beaker / Concentration of Green Food Coloring / Transmittance
(0 – 100%) / Absorbance
(0 – 2)
B / 1 drop per 200 mL water
C / 5 drops per 200 mL water
D / 10 drops per 200 mL water
Unknown / ?
  1. Empty out the cuvette and obtain a sample of the unknown solution at the “filling station.”
  1. Question: Compare the unknown sample to the solutions in beakers B, C, and D. What would you predict as the concentration of green food coloring in the unknown solution? Why?

I Can predict: A. Concentration, of unknown solution

B. Evaporation of unknown solution

C. My own prediction______

  1. Using the spectrophotometer, determine the absorbance and transmittance of the unknown solution. Record the values onTable C.
  1. Graph:Use the absorbance data from Beakers B, C, and D to create a concentration curve.
  1. Determine which variable is the independent variable and which is the dependent variable. Label each axis appropriately.
  2. Draw a best fit line. A line of best fit is a line that is drawn through the midpoint between all of the points without connecting each point.

List three things that you learned about absorbance and transmittance.

a.Absorbance and transmittance have an ______relationship.

b.As the concentration of the food coloring increases the absorbance ______.

c.As the concentration of food coloring increases the transmittance ______.

1.How does the amount of food coloring in solutions B, C, and D affect how much light will be absorbed by the solutions?

  1. The higher the concentration of food coloring, more light was absorbed. As the concentration of green food coloring increased from one to ten drops of food coloring per 200 mL of water, the absorbance values increased.
  2. The higher the concentration of food coloring, less light was absorbed. As the concentration of green food coloring increased from one to ten drops of food coloring per 200 mL of water, the absorbance values decreased.
  3. Not enough information to determine.

2.How does the amount of food coloring in solutions B, C, and D affect how much light will be transmitted by the solutions?

  1. The higher the concentration of food coloring, more light was transmitted. As the concentration of green food coloring increased from one to ten drops of food coloring per 200 mL of water, the transmittance values increased.
  2. The higher the concentration of food coloring, less light was transmitted. As the concentration of green food coloring increased from one to ten drops of food coloring per 200 mL of water, the transmittance values decreased.

3.Study the concentration curve. What is the concentration of food coloring in the unknown sample?

  1. Approximately 8 drops of food coloring per 200 mL water.
  2. Approximately 7 drops of food coloring per 200 mL water.
  3. Approximately 10 drops of food coloring per 200 mL water.

4.Looking at your concentration curve, if you had an unknown solution with nine drops of food coloring, what would be the absorbance?

A.The absorbance would be between 1.1 and 1.2.

B.The absorbance would be between 1.1 and 1.8.

C.The absorbance would be between 1.1 and 1.6

5.What is the relationship between the absorption and transmission of light through transparent substances?

  1. There is an inverse relationship between the amount of light that is transmitted versus that which is absorbed as light interacts with a transparent liquid. The more light that is transmitted, the less that is absorbed. As more light is absorbed, less is transmitted through the transparent medium.
  2. There is an transverse relationship between the amount of light that is transmitted versus that which is absorbed as light interacts with a transparent liquid. The more light that is transmitted, the more that is absorbed. As more light is absorbed, less is transmitted through the transparent medium.

6.An artist is using a blue dye a friend gave her to color strips of cotton cloth for a rug she is making. She realizes that she will not have enough dye to complete staining the white cotton cloth. She knows her friend started with 2 liters of water, and then added blue dye until she obtained the blue color she wanted. How could she use a spectrophotometer to know exactly how much blue dye to add to the 2 liters of water?

The artist would first determine the______of the blue dye solution she is using. For example, if the transparency of the dye solution and it is 75%. She would use this reading as a guide when mixing the blue dye with the water. She would use the s______to make sure that the transparency of the new dye solution is also 75%.

Light Investigation ONE

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