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 Form 4 Chemistry lessons on electrochemistry

Action of potassium dichromate (VI) on iron (II) ions (Fe2+):

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Answer Text:
Action of potassium dichromate (VI) on iron (II) ions (Fe2+):
(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.
figelectrochemistry11820201524.JPG
Note:
-The oxidation number of dichromate ions in K2Cr2O7 decreases from 6 to 3 (in Cr3+) hence reduction; while oxidation number of iron increases
from 2 (in Fe2+) to 3 (in Fe3+); hence oxidation;
-The presence of Fe3+ at the end of the reaction can be detected by adding sodium hydroxide solution to form a red brown precipitate of Fe(OH)3;


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