Chemistry Problem: Le Chatelier's principle?

Question

I somewhat understand Le Chatelier's Principle and equilibrium but this lab hasn't really explained much which is giving me a hard time answering its Analysis Questions. Please help.



"Explain why BTB is green in neutral water solution. In terms of Le Chatelier's principle why does it turn yellow when acid is added, and blue when base is added?"




I always thought BTB turns these colors because of its function as an acid/base detector. I didn't know there was an inside explanation behind it. How to explain this behavior in terms of Le Chatelier's Principle?

Answer 1

HBTB dissociates into H+ and BTB-, so think of it as an equilibrium reaction between HBTB and H+ and BTB ion:

C27H28Br2O5S (yellow)↔ H+ + C27H27Br2O5S- (blue)

When the solution is at equilibrium, it is a green color because it is a mixture of the two compounds. If you add acid, the equation shifts to the left because H+ is a product and therefore by adding acid you are increasing product. If you add base, the equation shifts to the right because the base neutralizes the H+, removing product.

Answer 2

This is sort of a chicken and the egg type problem. BTB 'works' because it is an organic dye chemical that has one form in acid solution and another in basic solution. In one form, the dye emits a yellow color; the other, a blue color; and in neutral pH, the in-between green color.

Answer 3

Endothermic reactions have the enthalpy substitute on the reactants section. Exothermic reactions have the enthalpy substitute on the products section. Enthalpy is the warmth content textile of the equipment in case you have been thinking so having it on the terrific could propose that the equipment is liberating warmth or exothermic.