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Form 4 Chemistry lessons on electrochemistry

Action of potassium dichromate (VI) on iron (II) ions ( $Fe^(2+)$ ):

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Answer Text:
Action of potassium dichromate (VI) on iron (II) ions ( $Fe^(2+)$ ):
(i). Procedure:
- A solution containing iron (II) ions is added into a solution of oxidized potassium dichromate (VI).
(ii). Observations:
- The orange solution of potassium dichromate turns green.
(iii). Explanations:
- The iron (II) ions are oxidized to iron (III) ions
- The chromium (VI) ions (orange) are reduced to chromium (III) ions
- This is thus a REDOX reaction.

Note:
-The oxidation number of dichromate ions in $K_2Cr_2O_7$ decreases from 6 to 3 (in $Cr^(3+)$ ) hence reduction; while oxidation number of iron increases
from 2 (in $Fe^(2+)$ ) to 3 (in $Fe^(3+)$ ); hence oxidation;
-The presence of $Fe^(3+)$ at the end of the reaction can be detected by adding sodium hydroxide solution to form a red brown precipitate of $Fe(OH)_3$ ;