A bidentate ligand forms two coordinate bonds from two donor atoms; use the structure to identify both lone-pair donors and the resulting coordination number.
21
Iron Chemistry
Iron is a typical transition metal. Due to the similar energies of the 3d and 4s electrons, iron forms compounds in a number of oxidation states.
Iron(II) and iron(III) are the most common oxidation states, and iron(III) is the most stable.
Iron ions form many complexes, including that in haemoglobin which is responsible for oxygen transport in the blood of most vertebrates. The haemoglobin-iron complex with oxygen is responsible for the red colour of blood.
Iron(III) ions may be detected in solution by the addition of thioglycolic acid (). All the water ligands of the iron(III) ion are replaced giving a complex with an intense red colour which can be detected in very low concentrations.
The complexes of iron(II) and iron(III) usually have a coordination number of six and are octahedral but the chloro complexes have a coordination number of four and are tetrahedral.
Iron and its compounds can act as catalysts. The element catalyses the Haber process, acting as a typical heterogeneous catalyst. However, the compounds and complexes of iron are usually homogeneous catalysts.
The presence of iron in sodium carbonate can affect its properties; the higher the quality of the sodium carbonate, the lower the proportion of iron.
The proportion of iron in a laboratory grade anhydrous sodium carbonate was listed as less than 20 ppm by mass.
In an experiment to check this specification, 20 g of the sodium carbonate was dissolved in sulfuric acid, and thioglycolic acid added in excess to form the iron(III) thioglycolic acid complex, . The solution was made up to in a volumetric flask and thoroughly mixed.
Colorimeter calibration graph
The transmittance of the resulting solution was determined using a colorimeter and found to be 39.8%.
Suggest what type of ligand thioglycolic acid is in the iron(III) thioglycolic acid complex. Justify your answer.