the copper ammonia is blue, but its maximum absorption is at 615 nm, whic is orange. Why?

Question

This was done in a visible absorption spectroscopy: Determination of Cu (II) experiment and i don't know how to answer this question...

Answer 1

Any substance appears coloured because it absorbs all other wavelengths of the visible spectrum other than the wavelength of its colour.i.e if a substance is blue in colour then it absorbs all other wavelenths of the visible spectrum including red,orange yellow, green except those pertaining to the blue region of the spectrum. Hence when these wavelenths strike the retina of the eye ,we perceive it as a blue coloured substance.
Now though it absorbs all other wavelenths ,it absorbs maximally those of a coloured region complementary to its physical colour.Thus for blue the complementary colour is orange(oppt ends of the spectrum),for violet eg KMnO4 it is red etc.So if you have to study the absorption power of a blue solution you have to use an orange filter in the colorimeter and for an orange coloured solution eg K2Cr2O7 you will use a blue filter.

Answer 2

Good buffers for measuring difference spectra ideally should not absorb light in the wavelength range of the experiment. For work in the near-UV, buffer absorbance should be small above 230 nm, and indeed most of the solvents commonly used in biochemical experiments do not absorb in this spectral region . Buffer absorbance is a major problem, however, in the far-UV region below 220 nm, because buffers that contain carboxyl and/or amino groups absorb light in this wavelength
range. Buffers with negligible absorbance in the far-UV include phosphate, cacodylate, and borate.

Answer 3

The colour of the solution is going to be the one corresponding to wave lengths where absorption is minimal-whatever is absorbed is in a way "lost" from the light passing through the solution.

Answer 4

That's how the colors you see work. Substances absorb the color opposite to what you see. You can't see the absorbed color, the color opposite that on the color wheel is what is reflected. That's what you see, the reflected light. Blue is opposite orange, you see blue, because the molecules absorb the orange, and it's gone from sight.