UV visible spectroscopy

[gordda]

Howdy,
i was wondering is anyone knows how a UV-visible spectroscopy works and how it differs to a double beam scanning spectrophotometer?
i know that UV visible spectroscopy needs a radiation source that is passed into a silt and then in a monochromator but how do u know how to poistion the monochromator to produce a red light to let's say to pass through a blue solution of CuSO4. And double beam scanning spectrophotometer uses motor what do those serve for?

and i have another question about equilibrium. if a 0.1 mole of N2O4 is introduced into 1L flask. the N2O4 dissociates into NO2 at equilibrium. 0.06 mole of N2O4 remain. Calculate the equilibrium constant for the reaction.
N2O4----->2NO2

Any help for any of the two questions would be awesome
Thanx :)

 

[Gokul43201]

UV-Vis spectroscopy is a technique for analyzing samples through the excitation and emission spectra of known constituents. A double beam Scanning Spectrophotometer is an (expensive piece of) instrument that is used for such a measurement. It is more reliable than a (cheaper) single beam spectrophotometer, as it splits the incident beam, directing one part to the sample being analyzed and the other to a blank (reference sample). This way, variations in the sample composition as well as drift in the lamp output is eliminated.

As far as I'm aware, the optical components (including the monochromator) are positioned so as to make the beam pass through the sample/s (when placed in the sample holder/s). Adjustments to settings will depend on the exact model of the instrument being used.