If a solution appears yellow, approximately what wavelength of light is it absorbing? 400 nm 470 nm 520 nm 580 nm 630 nm 700 nm
The Correct Answer and Explanation is:
Correct answer: 470 nm
When a solution appears yellow, it means that the color yellow is being transmitted or reflected to our eyes. In color theory and spectroscopy, the observed color of a solution is typically the complement of the color it absorbs. This concept is based on the visible light spectrum, which ranges from about 400 nm (violet) to 700 nm (red). Each color in this spectrum corresponds to a specific wavelength of light.
Yellow is approximately centered around 580 to 590 nm in the visible spectrum. The complementary color of yellow is violet-blue, which falls in the 470 nm range. Therefore, a solution that appears yellow is most likely absorbing violet or blue light, not yellow itself.
Here is a simplified complementary color relationship in terms of wavelengths:
- Red (absorbs green, ~520 nm)
- Orange (absorbs blue-green, ~500 nm)
- Yellow (absorbs violet-blue, ~470 nm)
- Green (absorbs red, ~630 nm)
- Blue (absorbs orange, ~600 nm)
- Violet (absorbs yellow-green, ~560 nm)
Since the solution appears yellow, it is not absorbing light near 580 nm (which is the wavelength of yellow). Instead, it absorbs the opposite on the color wheel — in this case, violet-blue light, close to 470 nm. This is why 470 nm is the correct choice.
Understanding which wavelengths are absorbed and which are transmitted or reflected is a key concept in both analytical chemistry (such as UV-Vis spectroscopy) and color perception. It allows scientists to determine the presence of specific substances in a solution based on their color and absorption characteristics.
