Answer:
See below
Explanation:
a) Adding HCl
HBTB is yellow in acid solution.
b) Adding NaOH
HBTB is blue in basic solution.
c) Explanation
HBTB is a weak acid in which the undissociated and ionized forms have different colours.
[tex]\underbrace{\hbox{\text{HBTB }}}_{\hbox{\text{yellow}}} + \text{{ H$_{2}$O}}\rightleftharpoons \text{H$_{3}$O$^{+}$} +\underbrace{\hbox{\text{ BTB$^{-}$}}}_{\hbox{\text{blue}}}[/tex]
Around pH 7 , the indicator consists of roughly equal amounts of the yellow and blue forms, so it appears green
According to Le Châtelier's Principle, if you apply a stress to a system at equilibrium, it will respond in a way that will relieve the stress.
When you added HCl, you increased the concentration of H₃O⁺. The system responded in a way that would decrease the H₃O⁺. That is, the position of equilibrium shifted to the left and produced more of the yellow form.
When you added NaOH, the base removed some of the H₃O⁺. The system responded in a way that would increase the H₃O⁺. That is, the position of equilibrium shifted to the right and produced more of the blue form
