Cobalt yellow - K3Co(NO2)6ĚH2O
Cobalt yellow, also known as potassium hexanitritocobaltate (III) monohydrate. This is used as a yellow pigment in certain paints. It is fairly stable, but on acidification it decomposes and on addition of sulfide, it is turned in black cobalt sulfide. This is a potassium salt, which is only very sparingly soluble.