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UV vis (1 Viewer)
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synthesisFR
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200-400nm is the uv range right
main use of uv vis on organic compounds is to detect conjugation so it should be A
main use of uv vis on organic compounds is to detect conjugation so it should be A
wizzkids
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Agree with @Unovan this is a weirdly worded set of answers.
UV-Vis Spectroscopy relies on photons that are more energetic than infrared, so these photons are not absorbed in rotation, translation or stretching of bonds. These photons are absorbed in electron energy transitions.
(A) is sort-of correct because UV spectroscopy is sensitive to the energy levels of bonding electrons.
(B) is incorrect because it has got nothing to do with molecular mass
(C) is incorrect because if we assume the three samples contain the same solute, they have quite different absorbance so their concentrations are not the same
(D) is probably incorrect. The visible spectrum extends from 300 nm to 700 nm and we have no data in that part of the e-m spectrum. If we assume these samples don't absorb in that part, so they are probably colourless, but we can't tell for sure.
UV-Vis Spectroscopy relies on photons that are more energetic than infrared, so these photons are not absorbed in rotation, translation or stretching of bonds. These photons are absorbed in electron energy transitions.
(A) is sort-of correct because UV spectroscopy is sensitive to the energy levels of bonding electrons.
(B) is incorrect because it has got nothing to do with molecular mass
(C) is incorrect because if we assume the three samples contain the same solute, they have quite different absorbance so their concentrations are not the same
(D) is probably incorrect. The visible spectrum extends from 300 nm to 700 nm and we have no data in that part of the e-m spectrum. If we assume these samples don't absorb in that part, so they are probably colourless, but we can't tell for sure.
Short version - BAD QUESTION. I agree that (B) and (C) are unreasonable, and (A) and (D) may be true... or not... and we lack the information to decide.
With no information about the absorbance beyond the range of wavelengths given, guessing that they have similar (lack of) absorbance at longer wavelengths (and so are colourless) is at least consistent with the low levels of absorbance at the edges of the spectra shown. Trying to infer anything about the structure and bonding is equally a guess... similar structures can have similar spectra, which is why coloured acid-base indicators usually have different structures in their acidic and basic forms, but similar spectra provide far from definitive proof of structural similarity.
This question looks like it comes from an Independent paper, which had a similarly inaccurate portrayal of UV-Vis Spectroscopy in a question on tartrazine in the past. At HSC level, the only things that can be guessed from UV-Vis are conjugation in organic compounds and accessible d orbital transitions in transition metal complexes.
This is why many transition metal complexes are coloured - think FeSCN2+ or why colourimetry works. TM complexes aren't abosrbing in the UV-Vis range because of conjugation of multiple bonds.