Final answer:
In acidic solution, the color of dichromate ions changes due to redox reactions with other ions. The pH affects the equilibrium between dichromate ions and HCrO4- ions, causing a change in color. The formation of different complexes and ions during redox reactions in acidic solution contributes to the color change.
Step-by-step explanation:
In acidic solution, the color change of dichromate ions (Cr₂O² ¯) occurs due to the redox reaction with iodide ions (I¯), resulting in the formation of a green Cr³+ complex and brown I₂ (aq) ions. The balanced equation for this reaction is: Cr₂O²¯(aq) + I¯(aq) → Cr³+ (aq) + I₂ (aq). In acidic solution, the dichromate ion is reduced to Cr³+ and changes from yellow to green.
The change in pH affects the equilibrium between dichromate ions (Cr₂O²¯) and HCrO4¯ ions. At a pH between 2 and 6, CrO4²- forms HCrO4¯, which is in equilibrium with dichromate ion. The balanced reaction is: 2HCrO4 (aq) → Cr₂O7²- (aq) + H₂O(l). At other acidic pH values, Cr³+ forms and the balanced reaction is: 4Cr³+ (aq) + 12H₂O(l).
Overall, the color change of dichromate ions with pH can be attributed to the formation of different complexes and ions during redox reactions in acidic solution.