The structure of the polydentate ligand, EDTA4—, is shown in Fig. 4.1. :0: :0: :O-CCH2 CH2C-O: NCH₂CH₂N :O-CCH CH₂C- :0: :0: Fig. 4.1 The stability constants, at 298K, of five octahedral complexes are given in Table 4.1. Table 4.1 complex Kstab [Cu(EDTA)]2- 6.31 x 1019 [Cr(EDTA)]2- 1.00 x 1013 [Cr(EDTA)]- 1.00 x 1024 [Fe(EDTA)]2- 2.00 x 1014 [Fe(EDTA)]- 1.26 x 1025

1. (a)Define stability constant.[1]
2. (b)Calculate the oxidation states of Cu in [Cu(EDTA)]2– and Cr in [Cr(EDTA)]-. Cu ............................................ Cr ............................................[1]
3. (c)Deduce the number of lone pairs donated by each EDTA4— ligand in a single [Fe(EDTA)]2– complex ion.[1]
4. (d)Identify the most stable complex in Table 4.1. Explain your choice.[1]
5. (e)In a solution at equilibrium at 298K, [[Cu(H2O)6]2+] = 3.00 × 10–10 moldm¯³ and [EDTA4–] = 5.00 × 10–12 moldm−3. Use the expression for Kstab to calculate the concentration of [Cu(EDTA)]2– in this solution. Show your working. [[Cu(EDTA)]2-] = ............................ moldm-3[2]
6. (f)A solution of [Cu(EDTA)]2– ions is pale blue while a solution of [Cu(NH3)4(H2O)2]2+ ions is deep blue. Explain this difference in colour.[2]

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