Question

[Cu(NH3)4]^+2 solutions exhibit a deep blue-violet color. How can you use spectrophotometry to confirm that this reaction has occurred and that the product formed is in fact tetraamminecopper (ll) sulfate? would you expect the wavelength of maximum absorbance (lambda max) for Cu(NH3)4^+2 to be greater than or less than lambda max for Cu(H20)6^+2? explain

Answer 1

One would record the UV-Visible absorption spectrum of teh solution and compare it with the literature spectrum of [Cu(NH3)4]2+. 

Answer 2

Answer : Use of spectrophotometry to study the absorbance changes during the course of reaction which can confirm that tetraamine copper(II) sulfate is formed or not is by comparing the absorbance of the solution with the literature absorbance value of tetraamine copper(II) sulfate. After comparison if both are found to be almost similar then it can be confirmed that tetraamine copper(II) sulfate is the product formed.

The wavelength of
`[Cu (NH_(3))_(4)]^(2+)` is less than λ max for
`Cu_(2+)` because it absorbs in the range of shorter wavelength of yellow light. Therefore, the solution appears to be deep blue-violet color.