Question

What is the purpose of sulfuric acid, hydroxylamine hydrochloride and sodium acetate in 1, 10-phenanthroline determination of total iron? Also provide the balanced equation for hydroxylamine hydrochloride in this experiment. (NH₄)₂Fe(SO₄)₂・6H₂O is given. Sulfuric acid is used in dissolving the (NH₄)₂Fe(SO₄)₂・6H₂O and after diluted (NH₄)₂Fe(SO₄)₂・6H₂O is taken for specific volume and other two is added to the specific volume of taken diluted (NH₄)₂Fe(SO₄)₂・6H₂O solution.

Answer 1

Use of NH₂OH.HCl :- It is a spectroscopic method of determination iron. Fe in its +2 oxidation state form red-orange color complex with 1,10-phenanthroline having wavelength ~500 nm. However, Fe(II) is unstable and readily oxidize to Fe(III) in presence of air. Therefore, hydroxylamine hydrochloride is used as reducing agent if small quantity of Fe(III) is present in the sample. Other reducing agents like sodium sulfite or stannous chloride can be used. But hydroxylamine hydrochloride is found to be most efficient (Journal of Dairy Science, vol 45, 1945, 401-412).

Use of Acetate buffer :- CH₃COONa-CH₃COOH is used as buffer solution to maintain P^H at the range 2-4. In this P^H range, Cu (an interfering radical), if present, can not react with 1,10-phenanthroline to form complex and the result would accurate.

Use of H₂SO₄ :- It is used to dissolve ferrous ammonium sulphate to prepare sample solution.