3K[Sn(OH)3] + 2K2CrO4 + 5KOH + 8H2O → 2K3[Cr(OH)6] + 3K2[Sn(OH)6]
Potassium trihydroxostannate(II) react with potassium chromate, potassium hydroxide and water to produce potassium hexahydroxochromate(III) and potassium hexahydroxostannate(IV). Potassium hydroxide - concentrated solution.