Determination of metal salts in the presence of mineral acids by a combination of turbidimetric and catalytic thermometric titrimetry

Abstract

Water-soluble salts of copper(II), nickel, chromium(III), iron(III), aluminium, cobalt, manganese(II), cadmium, zinc and lead(II) are determined titrimetrically in amounts down to 0.1 mequiv. in the presence and absence of hydrochloric, nitric and sulphuric acids. Ammonium salts are determined in the absence of free acids. When the mixture of metal salt and acid is titrated with aqueous potassium hydroxide, the end-point corresponding to the neutralisation of the free acid is determined by the onset of turbidity caused by precipitation of the hydroxide of the metal by the first excess of titrant. The titration is continued, and when all of the metal hydroxide is precipitated the final excess of titrant initiates the thermometric indicator reaction. The thermometric indicator, acetaldehyde, is diluted 1 + 1 with water to ensure solubility of the metal salts.

The method has been used to analyse four representative electroplating solutions for free acid and total metal content, the free acids being boric, acetic, succinic and glycollic acids.