a.) Removal of chemically bound impurities, e.g. corrosion products / oxidation products, by means of a pickling agent. b.) Roughening of surfaces, especially plastic surfaces. c.) Etching of printed circuit boards with sodium persulfate.
To a.)

In order to galvanize a metal surface properly, it must be active, i.e. an electron exchange (reduction of metal ions) must take place unhindered.

In addition, the substrate surface must be solid to prevent the galvanic layer from lifting off, i.e. a good bond between the galvanic layer and the workpiece surface must be guaranteed. Often, however, the surface of the workpieces is covered with tarnish, rust, oxide, salt layers and the like which do not meet the above requirements. These layers must therefore be removed. In addition to the mechanical treatment, a chemical treatment, pickling, is often also suitable.