Question

Chemistry Lab Help!

Answer 1

Vanadium can have many oxidation states. Based on these oxidation states (i.e., the number of electrons present around the central metal ion) and the nature of the species bonded to the metal ion, vanadium compounds can appear in a variety of colors, including green and violet.

i. Explain how the appearance (color) of the solution is related to the wavelength of light that is absorbed? (Think: What wavelengths of light are present? Do you see the light transmitted or absorbed?)

ii. What wavelength of light would you expect the green species to absorb in a UV-Vis spectrum?

iii. What wavelength of light would you expect the violet species to absorb in a UV-Vis spectrum?

iv. Dr. Hayden trusty lab tech John was trying to synthesize a new vanadium compound, but his reaction yielded a solution that appears brownish.
a. Dr. Hayden points out that UV-Vis spectroscopy does not definitely prove that the solution is a mixture, and that it might be that there is a single compound that is causes the brown appearance. John decides to run a tlc separation. Under what conditions would a tlc separation be definitive? Under what conditions would the tlc procedure be inconclusive?

b. John finds that the brown appearance means that there is a mixture of green and violet compounds. Describe a procedure (using one of the techniques we have used this term) that would allow John to quantitatively determine the ratio of green to violet.

Answer 2

here is the second one @aaronq

Answer 3

I knnw that the light seen is the one reflected.

Answer 4

I also know that the absorption of green is about 530nm and for violet its about 410

Answer 5

iv. a)

do you know what thin-layer chromatography (TLC) is?

it's basically a method that uses a polar surface (the stationary phase) and non-polar solvent (the mobile phase) to separate compounds that is dependent on the selective retardation of a given compound (by a favoured association with one of the phases).

So, the TLC will tell you that there is several compounds in there, given that they have very different polarities (otherwise they'll look like the same spot). For example Mix 1 separates very well, but mix 2 doesn't and so i'll look like the same spot on the plate and you won't be able to know that there is more than 1 compound.



b) what techniques have you used?