Chromium(III) hydroxide formation, 3 of 3. When 2.9M ammonium hydroxide (NH4OH) is poured into a beaker with 0.025M chromium(III) potassium sulfate (KCr(SO4)2), green chromium(III) hydroxide (Cr(OH)3) is formed. The reaction is Cr3+ + OH- -> Cr(OH)3. This reaction had been used as a test for Cr3+ ions in classic qualitative inorganic analysis.