Correlate the observations with Le Chatelier's principle?

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The discussion centers on the application of Le Chatelier's principle to a chemical reaction involving iron(III) nitrate (Fe(NO3)3) and potassium thiocyanate (KSCN) in a solution that forms the complex ion Fe(SCN)2+. In test tube 1, the addition of Fe(NO3)3 does not change the color, indicating no shift in equilibrium. In test tube 2, the addition of KSCN results in a darker red color due to increased formation of Fe(SCN)2+. Test tube 3 shows a color change to yellow upon adding NaOH, as Fe(OH)3 precipitates, removing Fe3+ ions and shifting the equilibrium left. Test tube 4 demonstrates dilution effects, leading to a lighter color as the concentration of the complex decreases.

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(see image below) A solution made with 3mL of 0.1 M Fe(NO3)3, 3mL 0.1 M KSCN, and 35 mL of distilled water is poured into 4 test tubes. The color of the solution in each test tube is a blood red due to the formation of Fe(SCN)2+.

Test tube 1: a few drops of 0.1 M Fe(NO3)3 are added (the blood red color remains the same)

Test tube 2: a few drops of 0.1 M KSCN are added (the blood red color turns darker)

Test tube 3: 25 drops of 6 M NaOH are added (the blood red color turns to yellow)

Test tube 4: more distilled water is added (the blood red color becomes lighter in appearance)Okay, I'm confused when it comes to correlating my color observations of each test tube with Le Chatelier's principle. Test tube 1 and 2 throw me off because shouldn't they both turn darker because more Fe3+ and SCN ions are added which help produce more Fe(SCN)2+? Also, why does test tube 3 turn yellow, where does the yellow color come from? Test tube 4 is obvious because the concentration lessons. Please help, thanks you.

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When you add NaOH, the OH- ions combine with the Fe+3 ions to form a precipitate, Fe(OH)3, effectively removing the Fe+3 ions from solution. This causes the system to shift to the left, to replace the Fe +3 ions.
 
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imconfused said:
solution made with 3mL of 0.1 M Fe(NO3)3, 3mL 0.1 M KSCN

Test tube 1: a few drops of 0.1 M Fe(NO3)3 are added (the blood red color remains the same)

Think about stoichiometry of the reaction.

Test tube 2: a few drops of 0.1 M KSCN are added (the blood red color turns darker)

This system is much more complicated and FeSCN2+ is not the final product. All complexes up to Fe(SCN)63- are produced.
 

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