A and B formed in the following reactions are: CrO2Cl2 + 4NaOH A + 2NaCl + 2H2O, A + 2HCl + 2H2O2 B + 3H2O
- A = Na2Cr2O7, B = CrO5
- A = Na2CrO4, B = CrO5
- A = Na2Cr2O4, B = CrO4
- A = Na2Cr2O7, B = CrO3
Answer
(2) A = Na2CrO4, B = CrO5
Solution
CrO2Cl2 + 4NaOH Na2CrO4 + 2NaCl + 2H2O ⇒ A = Na2CrO4 (yellow)
∵ in alkali chromium(VI) stays as chromate CrO42- (dichromate needs acid)
Na2CrO4 + 2HCl + 2H2O2 CrO5 + 2NaCl + 3H2O ⇒ B = CrO5 (blue chromium peroxide)
(the second equation as printed omits 2NaCl)
Answer: (2)