MCAT® ExamChemical and Physical Foundations of Biological SystemsMedium
A student is analyzing a reaction involving a transition metal complex. They determine that the central metal ion has a coordination number of 6 and is bonded to six identical ligands. If the complex absorbs red light, what color is the complex most likely to appear?
- AOrange
- BBlue-green
- CRed
- DYellow
Show answer & explanationAnswer & explanation
Correct answer: B. Blue-green
The color of a transition metal complex is determined by the wavelengths of visible light that it *does not* absorb, but instead reflects or transmits. If a complex absorbs red light, its perceived color will be the complementary color to red. On the color wheel, the complementary color to red is blue-green (or cyan).
Why the other options are wrong
- A. Incorrect. Orange is complementary to blue. If the complex absorbed red, it would not appear orange.
- C. Incorrect. If the complex absorbs red light, it would not appear red; it would appear the complementary color.
- D. Incorrect. Yellow is complementary to violet. If the complex absorbed red, it would not appear yellow.
Complementary Colors
Complementary colors are pairs of colors that, when combined, produce white light (or black pigment). In chemistry, they describe the perceived color of a substance that absorbs a specific wavelength of light.
- If a substance absorbs a color, it appears as its complementary color.
- Common complementary pairs: Red ↔ Blue-Green (Cyan), Orange ↔ Blue, Yellow ↔ Violet, Green ↔ Magenta (Red-Violet).
- Transition metal complexes absorb specific wavelengths due to d-orbital splitting.
Memory trick: Opposite on the Wheel is what you'll See.