P 2186 (OTTO) Potassium chromate, solution 5% w/v Cas 7789-00-6 - used as an indicator in the volumetric estimation of Mohr chloride. P 2186 (OTTO) Potassium chromate, solution 5% w/v Cas 7789-00-6 - used as a corrosion inhibiting additive during the surface preparation of mild steel.