What’s in the water? Colorimetry and conductivity of solutions Presenter: Part 2

Investigation 13C: Colored Solutions Chapter 13 How does the light that is absorbed into the solution related to the color of the solution?

Think About It Describe each of the colors of light as it is shined on the crystals below. Why is the blue light the only light that is reflected? What happened to the red and/or green light?

Safety Considerations Follow these important safety precautions in addition to your regular classroom procedures. Wear safety goggles at all times. Lab Preparation The solutions are made by putting one drop of food coloring per 100ml of water. However, the yellow solution needs two drops per 100 mL. If the colored solution is reading an absorbance of greater than 1.5, the color is too dark and should be diluted with some more water.

What You Will Need Device with SPARKvue software / Colorimeter / Cuvettes (5) Food Coloring (red, green, blue, yellow) / Wash bottle with distilled water Test tube rack / Test tubes, 20 mm x 150 mm (5) Need pic of heater stirrer

Connecting a Sensor Turn on the colorimeter sensor and then connect it using Bluetooth.

Open the Lab File Open the 13C Colored Solutions lab file in SPARKvue under Experiments > Essential Chemistry.

Procedure Put 1 drop of each food coloring in each test tube. Add 10 mL of water to each test tube and mix. Using the pipette, take 3 mL of each solution and put it in the cuvettes. You should have four cuvettes, each with a different color. Place 3 mL of water in the fifth cuvette. This cuvette will be used as a reference in your measurements.

Procedure Wipe off the sides of the cuvette with solution and water. Only handle it by the top, then close the lid. Calibrate the colorimeter with the distilled water (the water sample is called a “blank”). 10. Start data collection.

Procedure 11. Record the % Transmittance and absorbance at each available wavelength.

Procedure 12. Stop collecting data.

Analysis Soluti ons Red light Green light Blue light Orange light 660 nm 565 nm 468 nm 610 nm %T A water Red Green Blue Yellow

Analysis Soluti ons Red light Green light Blue light Orange light 660 nm 565 nm 468 nm 610 nm %T A water 100 0.00 Red 92.8 0.032 75.3 0.123 30.0 0.523 89.4 0.049 Green 27.5 0.561 36.9 0.433 33.7 0.473 7.1 1.150 Blue 19.8 0.704 21.6 0.666 72.3 0.141 3.1 1.502 Yellow 99.3 0.003 99.2 31.7 0.499 99.0 0004

Questions If a solution has a high transmittance for a certain color of light, what does that mean in terms of photons of light interacting with electrons in the solution? Use specific evidence from the Data Table to justify your answer.

Questions If a solution has a high transmittance for a certain color of light, what does that mean in terms of photons of light interacting with electrons in the solution? Use specific evidence from the Data Table to justify your answer. If the light goes through the solution, the photons are not interacting. One example could be the Red solution with a transmittance of 92.8.

Questions When a solution has a high transmittance for a certain color of light, does it also have a high absorbance for that color? Use specific evidence from the Data Table to justify your answer. 3. State the color of the solution which absorbed the most a) green light b) blue light c) red light

Questions When a solution has a high transmittance for a certain color of light, does it also have a high absorbance for that color? Use specific evidence from the Data Table to justify your answer. No. When the transmittance of light for a certain color is high the absorbance is very low. One example could be the red solution with an absorbance of 0.032.   3. State the color of the solution which absorbed the most a) green light b) blue light c) red light

Questions When a solution has a high transmittance for a certain color of light, does it also have a high absorbance for that color? Use specific evidence from the Data Table to justify your answer. No. When the transmittance of light for a certain color is high the absorbance is very low. One example could be the red solution with an absorbance of 0.032.   3. State the color of the solution which absorbed the most a) green light b) blue light c) red light red

Questions When a solution has a high transmittance for a certain color of light, does it also have a high absorbance for that color? Use specific evidence from the Data Table to justify your answer. No. When the transmittance of light for a certain color is high the absorbance is very low. One example could be the red solution with an absorbance of 0.032.   3. State the color of the solution which absorbed the most a) green light b) blue light c) red light red orange/yellow

Questions When a solution has a high transmittance for a certain color of light, does it also have a high absorbance for that color? Use specific evidence from the Data Table to justify your answer. No. When the transmittance of light for a certain color is high the absorbance is very low. One example could be the red solution with an absorbance of 0.032.   3. State the color of the solution which absorbed the most a) green light b) blue light c) red light red orange/yellow green

Questions Do the dye molecules in food color absorb a single color of light or a range of colors? How do you know? When light matches the color of the solution, is it mostly transmitted or absorbed? Justify your answer with data.

Questions Do the dye molecules in food color absorb a single color of light or a range of colors? How do you know? A range of colors. This is evident from the different shades of color that can exist. When light matches the color of the solution, is it mostly transmitted or absorbed? Justify your answer with data.

Questions Do the dye molecules in food color absorb a single color of light or a range of colors? How do you know? A range of colors. This is evident from the different shades of color that can exist. When light matches the color of the solution, is it mostly transmitted or absorbed? Justify your answer with data. The light that matches the color of the solution is mostly transmitted. For example, the red solution mostly transmitted red light.

Questions Consider the color wheel below. Red and green are considered complementary colors, as are violet and yellow. When light is shone through a solution that is a complementary color to that of the solution, is it mostly transmitted or absorbed? Justify your answer with data.

Questions Consider the color wheel below. Red and green are considered complementary colors, as are violet and yellow. When light is shone through a solution that is a complementary color to that of the solution, is it mostly transmitted or absorbed? Justify your answer with data. The complementary color has the highest absorbance. This is most evident in the blue solution since it mostly absorbed the complimentary orange color.

Questions What does the absorbance of red, green and blue tell us about the way the yellow color in our experiment is made? 


Questions What does the absorbance of red, green and blue tell us about the way the yellow color in our experiment is made? 
 For the yellow the most absorbed color is blue. The other colors are highly transmitted.

Questions Research the way color books and magazines are printed. Explain the acronym CMYK. Why do printers use CMYK color instead of RGB? 


Questions Research the way color books and magazines are printed. Explain the acronym CMYK. Why do printers use CMYK color instead of RGB? 
In the printing press days, to achieve color, each ink (cyan, magenta, yellow, and black) had its own plate. First the printer would lay down one color, wait for it to dry, lay down another color, and wait for it to dry and so on. Printing presses still work on that same theory to this day with the exception that offset printers can use a “spot” color which can be added to achieve a specific color (usually a Pantone color). As the printing age has progressed, the digital printer has come a long way, allowing printing in RGB as well.

Questions? loschiavo@pasco.com