Chemical workshop in IB DP program 28.06.18

One of the chemical workshops of the IB DP program was devoted to the solid-phase synthesis of cobalt-based dyes - CoO•ZnO (Rinman green) and CoO•Al2O3 (Cobalt blue).

Rinman green was synthesized in several stages. First, the carbonates of zinc (ZnCO3) and cobalt (CoCO3) were prepared by treatment of aqueous solution containing ZnSO4 and Co(NO3)2 (molar ratio 1:1) with a small excess of aqueous K2CO3 (Photos 1-3).

The Precipitate washed on a Schott filter (Photo 4, Video 1) with a large amount of distilled water (in order to remove soluble potassium salts) and dried (Photo 5).

Calcination of sediment in the muffle furnace at a temperature of 900-1000 °C for 30 minutes resulted in to the decomposition of cobalt and zinc carbonates to the corresponding oxides (Video 2). The video clearly shows how "trembling" of the solid due to CO2 emissions. The cup was removed from the oven, the residue was triturated to a state of fine dust. Repeated annealing of the oxides mixture (900-1000 ºС, 1 hour) led to the formation of a dark green CoO·ZnO.

Cobalt blue was synthesized in two stages. In the beginning, a solid mixture of Co(NO3)2·6H2O and Al(NO3)3·9H2O (1:1 molar ratio) was heated in a porcelain dish on an electric stove. At elevated temperatures, these crystalline hydrates melt in their own crystallization water to form a dark violet solution (Photo 6).

Heating was continued until the water was completely removed, after which the dry residue was grinded (Photo 7).

Calcination in a muffle furnace at a temperature of 900-1000 ºС for 45 minutes yields intense dark-blue CoO∙Al2O3 solid. This process shows the evolution of brown gas (NO2), which indicates the thermal decomposition of aluminium and cobalt nitrates.

See the photo report.