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LeChatelier's principle in equilibria

Observations:
1 1mL Ba(NO3)2 + 0.5mL K2CrO4 + drops HCl? + drops NaOH? "Ba(NO3)2=clear and colourless
Ba(NO3)2 + K2CrO4= yellow turbid solution (precipitate)
HCl= clear yellow solution (precipitate dissolved)
NaOH= yellowish turbid solution (precipitate returns by neutralizing acid) "
2 1mL Ba(NO3)2 + 0.5mL K2Cr2O7 + 10 drops HCl "Ba(NO3)2=clear and colourless
Ba(NO3)2 + K2Cr2O7= orange-yellow slightly cloudy solution (cloudy d/t reaction with distilled water))
HCl= clear yellowish solution (no precipitate) "
3 1mL Ba(NO3)2 + 5 drops HCl + 5 drops K2CrO4 "Ba(NO3)2=clear and colourless
Ba(NO3)2 + HCl= clear and colourless (acidified Barium Nitrate)
+K2CrO4= yellow clear solution (No precipitate d/t rapid conversion to dichromate) "
4 1mL Ba(NO3)2 + 5 drops CH3CO2H + 5 drops K2CrO4 "Ba(NO3)2=clear and colourless
Ba(NO3)2 + CH3CO2H (acetic acid)= clear and colourless
+K2CrO4= yellow cloudy solution (precipitate formed b/c acetic acid is a weak acid) "

1) Explain what happened in each test regarding Le Chateliers principle

2) When few drops if sodium fluoride solution are added to a solution containing iron (III) ions a colourless solution is obtained. However, when a few drops if sodium chloride are added to a solution
Fe³⁺(aq) + 6F‾ (aq) ⇋ FeF₆³‾(aq)
(pale yellow) (colourless)
containing iron (III) ions a pale yellow solution is obtained, with the yellow colour deepening as more sodium chloride is added.
Fe³⁺(aq) + 4Cl‾ (aq) ⇋ FeCl₄‾(aq)
(pale yellow) (Intense yellow)
Predict what will occur, if a solution of sodium fluoride is added to the solution prepared from the iron (III) and sodium chloride solutions. Justify your prediction in terms of Le Chatelier's principle.

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Ba 2+ + 2 NO3- + CrO42- + 2K+ ----> BaCrO4 + K+ + NO3-
colorless yellowish yellow ppt

Adding HCl is like adding H+ ions. The CrO42- ion will react with H+ to form the dichromate ion Cr2O72-. This amounts to a lower concentration of CrO42-, a reactant. In order to counter this stress on the equilibrium, the reaction will form more reactant which can happen if solid BaCrO4 dissolves.
Adding NaOH is like adding OH- ions. The added OH- will react with H+. This means that H+ added in the previous step will ...

Solution Summary

Some examples of LeChatelier's principle are explained using barium and iron salts equilibria.

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