Thermometric titration of thorium with EDTA in the presence of large excess of neutral sodium salts

Abstract

The thermometric titration of Th(IV) in the presence of neutral sodium salts, sulphuric acid or acetic acid with EDTA has been studied. The effect of each on the observed heat values for the titration is discussed. For sodium perchlorate media, Δ H values of −9 and −21 kJ/mole have been estimated for the formation of the Th(IV)-EDTA chelate at μ → 0 and μ = 0.5 (NaClO 4), respectively. The −Δ H values increase steadily with increase in concentration of sodium perchlorate up to at least 3 M. For the titration of Th(IV) in the presence of a large excess of sodium nitrate the use of sodium iodide as a masking reagent has been examined: large amounts of Bi and Cu(II) are masked and a masking effect is observed for small amounts of Ni.