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 tetraamminecopper (II) sulfate?

Answer 1

Spectrophotometry can confirm the formation of the tetraammine copper (II) sulfate complex by identifying its characteristic absorbance peak, which differs from that of a simple copper(II) sulfate solution due to the alterations in the electrons' energy states after complexation.

Step-by-step explanation:

To confirm that the complex ion tetraamminecopper (II) sulfate ([Cu(NH3)4]2+) has formed, you can use spectrophotometry, which measures the absorption of light by a solution at various wavelengths. When white light passes through a solution, certain wavelengths are absorbed by the solution. This absorption corresponds to the energy difference between the ground and excited states of the electrons in the compound. For copper(II) ions in a solution, such as copper(II) sulfate, they absorb light in the red part of the spectrum, causing the solution to appear pale blue. However, when ammonia is added to the solution and the tetraamminecopper (II) complex is formed, the color changes to a deep blue-violet due to the different arrangement of ligands around the copper ion, which alters the energy states of the electrons.

To perform the spectrophotometry, a sample of the solution to be tested is placed in a spectrophotometer. The instrument then passes light through the solution and measures the intensity of light before and after passing through the sample. The difference in intensity corresponds to the amount of light absorbed. By examining the absorbance at different wavelengths, you can identify the characteristic absorbance peak for the [Cu(NH3)4]2+ complex, confirming its presence in the solution.

Answer 2

Analyzing the wavelength of maximum absorbance

Step-by-step explanation:

Using spectrophotometry during the course of the reaction can confirm that the reaction took place.

The complex [Cu(NH₃)₄]²⁺ has a characteristic wavelength of maximum absorbance (
`λ_(max)` ), which can be looked up in literature. This characteristic λmax is different from the characteristic λmax of the reagents, as [Cu(NH₃)₄]²⁺ absorbs red-orange light and thus appears with a deep blue-violet color.