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Chemistry 151

Chemistry 151. Chemistry and Color (from an elementary school perspective). Electromagnetic radiation. Light is a form of energy that travels through space like a wave and is characterized by its wavelength. Electromagnetic radiation.

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Chemistry 151

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  1. Chemistry 151 Chemistry and Color (from an elementary school perspective)

  2. Electromagnetic radiation • Light is a form of energy that travels through space like a wave and is characterized by its wavelength.

  3. Electromagnetic radiation • Only certain wavelengths of light can be detected by the human eye.

  4. White Light • “White” light is actually composed of all colors in equal amounts.

  5. Color Perception • Specialized conecells in our eyes respond to visible light and signal color to the brain.

  6. Color Perception • There are three different kinds of human cone cells varying in their sensitivities to different colors of light: blue, green, and red. • Leads to trichromatic color vision. • Sometimes called long, medium and short cones.

  7. Color Perception • Birds have four different kinds of cones (one in the UV). • Dogs have only two (no green).

  8. Color Perception The Bird’s View • Birds have four different kinds of cones (one in the UV). • Dogs have only two (no green).

  9. Color Perception • A defect in one of the three types of cones leads to “color blindness,” difficulty in distinguishing colors.

  10. Color Perception • Objects appear colored when they reflect light of that color. • Red cones respond, signalling to the brain that the apple is “red”.

  11. Color Perception • Adding red, green, and blue light in equal amounts leads to white light. • Adding red, green, and blue light in unequal amounts leads to all possible colors of light. • Red, green, and blue are the primary colors of light.

  12. Color Perception • Pigments are molecules that absorb certain colors of light and reflect the others. • The brain integrates the responses of the cone cells to perceive the pigment’s color. The yellow filter absorbs blue light; reflects red and green.

  13. Absorbance of Light • A pigment generally absorbs light that is complementary to that observed. • Absorbance data can be correlated to the identity of pigment. Color Wheel

  14. Absorbance of Light • For example: a purple pigment absorbs yellow-green light.

  15. Absorbance of Light Food Coloring Data: Yellow: 425 nm (absorbs violet) Red: 522 nm (absorbs cyan) Blue: 610 nm (absorbs orange)

  16. Absorbance of Light • The absorbance of light can be measured with a spectophotometer.

  17. Magenta pigment absorbs green light. Absorbance of Light • The three primary colors of pigments arise from subtracting out one of the three primary colors of light.

  18. Absorbance of Light • The three primary colors of pigments arise from subtracting out one of the three primary colors of light. Magenta pigment absorbs green light. Yellow pigment absorbs blue light.

  19. Absorbance of Light • The three primary colors of pigments arise from subtracting out one of the three primary colors of light. Magenta pigment absorbs green light. Yellow pigment absorbs blue light. Cyan pigment absorbs red light.

  20. Color Perception • Adding magenta, cyan, and yellow pigments in equal proportions leads to black. • Adding magenta, cyan, and yellow pigments in unequal proportions leads to all possible colors of pigments. • Magenta, cyan, and yellow are the primary colors of pigments.

  21. primary colors secondary colors tertiary colors Primary Colors of Pigments • Equally adding adjacent pigments leads to the development of color wheels.

  22. yellow green red cyan blue magenta Complementary colors • Colors opposite each other on color wheels are complementary colors. • Pigments of complementary colors add in equal amounts to give black.

  23. Complementary colors Yellow and blue Magenta and green Red and cyan

  24. 2012: Color Wheels Primary and secondary colors are introduced to show that some colors are made when mixing other colors together. Students make their own color wheels using homemade paint.

  25. Colors in art • Paints are a homogeneous mixture of a pigment, which provides color, and a binder, which cements the pigment to the solid support after drying.

  26. charcoal brown ochre Pigments in nature • Early artists had primarily earth tones in their palettes, many mineral-based.

  27. hematite (Fe2O3 · nH2O) is a source of red, yellow, and brown ochre cinnabar (HgS) is a source of the red pigment vermilion azurite (2 CuCO3 · Cu(OH)2) Mineral-Based (Inorganic) Pigments

  28. 2010: Alien Rocks Students analyze rock samples from the newly discovered planet of Zircondrion to determine if they are similar to Earth minerals. Analysis includes: • Color • Iron? (absorbance of light) Properties such as magnetism and fluorescence • Chemical reactions

  29. Tyrian purple Madder lake (alizarin) Plant & Animal-Based (Organic) Pigments Indigo

  30. Common Sources of Pigments Marigolds Grape Juice Beets Cochineal Beetles Walnut hulls Kool-Aid

  31. CH112: Color Activity • Learning Goals: • Investigate the interaction of dyes with different fabrics. • Identify ionic and polar groups in dyes and fabrics. • Identify the different types of bonding interactions between dyes and fabrics.

  32. The chemistry of fraud detection History of blue pigment use Pigment/Metal Dates in use Azurite/Cu until 1800 Ultramarine/Al until 1828 Prussian Blue/Fe post-1704 Synthetic Ultramarine/Al post-1828 Cerulean Blue/Co, Sn post-1850 Manganese Blue/Mn post-1935

  33. 2008: Art Fraud Activity Last Friday, a priceless masterpiece was stolen from the little-known Waterville Museum of Old Weird Art. The painting was the masterpiece of the great Italian finger painter, Alfredo Fettuccini. However, yesterday the caretaker told police he forgot he had taken the painting home to clean it, and found it in his bedroom the next morning. An original painting by Fettuccini and the painting produced by the caretaker have been confiscated, packaged, and sent to the Colby Chemistry Lab for analysis. Alfredo Fettuccini 1600 - 1650

  34. The case of the missing masterpiece You suspect that the caretaker, Ebenezer Wheezingeezer, stole the real painting and replaced it with a fake. You will investigate the pigments used in the paintings and then look for clues on the paintings themselves. The Waterville Museum of Old Weird Art has granted you special permission to handle these rare paintings. The police are standing by, awaiting your judgment. Ebenezer Wheezingeezer 1950 - ????

  35. The case of the missing masterpiece • Experiment 1: • Absorbance spectra of the following pigments: • Pigment from the “Masterpiece” Ebenezer found • Pigment from a modern painting • Pigment found on the floor of the museum • Pigment from a preserved brush of Fettuccini • Pigment stain found on Ebenezer’s overalls

  36. The case of the missing masterpiece • Experiment 2: • Chemical reactivity of the pigments: • pH • Reaction with aspirin • Reaction with potassium hexacyanoferrate(II) Tests for Fe

  37. The case of the missing masterpiece • Experiment 3: • Examination for possible restoration: • Fluorescent paint detected with UV light

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