Provide an explanation/analysis for these observations using le chatellier\'s pr

Question

Provide an explanation/analysis for these observations using le chatellier's principle. (what chemical is yellow? what chemical is blue? why is the solution green?)

-started with 2 drops of aqueous Bromocresol Green Indicator and diluted it with 10 drops of DI water: HIn(aq)<--->H+(aq)+In-(aq) or HIn(aq)+H2o(l)<--->H3O+(aq)+In-(aq) *color=emerald green liquid

-now add the following stresses: add 1-2 drops of 0.1M HCl(aq) *color=orange liquid

-now add 1-2 drops of 0.1M NaOH(aq)   *color=purple liquid

-now add 1-2 drops of 0.1M HCl *color=red/orange liquid

Explanation / Answer

For bromocresol green, the HIn indicator non-ionized form is yellow, which goes to In- after losing a H+ and gives a blue color.

- When diluted with water, the increase in volume favors dissociation or ionization. Thus going from yellow to emerald green color.

- When we add H+ in the form of HCl, we have excess of H+ on the product side, which would combine with In- to regenerate HIn and establish equilibrium once again. This is according to LeChatellier's principle which states that any change in the reaction will cause the equilibrium shift to a side so as to reestablish equilibrium. the color changes to orange, that is less of dissociated form.

- when NaOH is added. HIn would get neutralized with added base and we would get more of In- species in solution. The color thus changes to purple.

- Finally If we add addition HCl to the solution, reformation of more of HIn would occur from In- state and thus the color changes to red/orange.

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