Chemistry Lab
INTRODUCTION:
The purpose of this experiment is to measure the formation constant of the tetraamminecopper(II) ion by colorimetry. Anhydrous copper sulfate (CuSO4) is white, which means that it does not absorb light in the visible region of the spectrum. The hydrated copper sulfate (CuSO4 - 5H2O) is blue. The structure of the compound can be represented more accurately as Cu(H2O)4 SO4 - H2O where four water molecules are bound to the copper ion and the fifth is a water of crystallization. The water molecules are arranged at the corners of a square, with the copper at the center. Such an arrangement is called square coplanar. The oxygen of each water molecule shares one pair of electrons with the central copper ion. The absorption spectrum of 0.01M copper sulfate is shown, in Figure 1, by the dotted line, A. Absorbance is plotted against wavelength in angstroms (Å). Notice that the compound absorbs light of wavelengths from 6000 to above 8000 Å, which is the yellow-to-red region of the visible spectrum. The light transmitted through the solution comes out richer in light of blue wavelengths (4000 to 5000 Å) than white light, and so the solution looks blue. When ammonia is added to a solution of copper(II) cation, a deep blue color is formed immediately. The blue color is due to the complex. ion Cu(NH3)42+.
Cu(H2O)42+ + 4NH3 Cu(NH3)42+ + 4H2O
This complex ion, the tetraamminecopper(II) cation, has a square co-planar geometry also. The absorption spectrum of this complex ion in 0.05M ammonia is shown in Figure 1 as the solid line, B. In this complex, also, the light of yellow and red wavelengths is absorbed more than the blue, so the solution appears blue. The tetraamminecopper(II) cation is the principal copper species present in ammonia solution of concentration 0.01 to 5M. However, at lower concentrations of ammonia, other copper species having 3, 2 or 1 molecules of ammonia may be present. At higher concentrations of ammonia, a
The purpose of this experiment is to measure the formation constant of the tetraamminecopper(II) ion by colorimetry. Anhydrous copper sulfate (CuSO4) is white, which means that it does not absorb light in the visible region of the spectrum. The hydrated copper sulfate (CuSO4 - 5H2O) is blue. The structure of the compound can be represented more accurately as Cu(H2O)4 SO4 - H2O where four water molecules are bound to the copper ion and the fifth is a water of crystallization. The water molecules are arranged at the corners of a square, with the copper at the center. Such an arrangement is called square coplanar. The oxygen of each water molecule shares one pair of electrons with the central copper ion. The absorption spectrum of 0.01M copper sulfate is shown, in Figure 1, by the dotted line, A. Absorbance is plotted against wavelength in angstroms (Å). Notice that the compound absorbs light of wavelengths from 6000 to above 8000 Å, which is the yellow-to-red region of the visible spectrum. The light transmitted through the solution comes out richer in light of blue wavelengths (4000 to 5000 Å) than white light, and so the solution looks blue. When ammonia is added to a solution of copper(II) cation, a deep blue color is formed immediately. The blue color is due to the complex. ion Cu(NH3)42+.
Cu(H2O)42+ + 4NH3 Cu(NH3)42+ + 4H2O
This complex ion, the tetraamminecopper(II) cation, has a square co-planar geometry also. The absorption spectrum of this complex ion in 0.05M ammonia is shown in Figure 1 as the solid line, B. In this complex, also, the light of yellow and red wavelengths is absorbed more than the blue, so the solution appears blue. The tetraamminecopper(II) cation is the principal copper species present in ammonia solution of concentration 0.01 to 5M. However, at lower concentrations of ammonia, other copper species having 3, 2 or 1 molecules of ammonia may be present. At higher concentrations of ammonia, a