Cr-CrCL3-Cr(OH)3-Cr2O3-Cr2(SO4)3-K2Cr2O7

1) 2Cr + 3CaCl2 = 2CrCl3 + 3Ca 2) CrCl3 + 3NaOH = Cr(OH)3↓ + 3NaCl 3) 2Cr(OH)3 = Cr2O3 + 3H2O 4) Cr2O3 + 3K2S2O7 = Cr2(SO4)3 + 3K2(SO4)3 5) Cr2(SO4)3 + 3Br2 + 16KOH  = K2Cr2O7 + 3K2SO4 + 6KBr + 8H2O