QUESTION IMAGE
Question
consider the following chemical reaction of bromothymol blue indicator. it appears yellow in undissociated form and blue in its dissociated aqueous solution.
\\\ce{hc_{2}h_{3}o_{2}(aq) \
ightleftharpoons h^{+}(aq) + c_{2}h_{3}o_{2}^{-}(aq)} \\
\quad\quad\quad\quad\quad yellow \quad\quad\quad\quad\quad\quad\quad\quad blue
what will be the color of the solution if a large amount of \\(\ce{h_{2}co_{3}}\\) is added?
\\(\bigcirc\\) the solution will remain yellow.
\\(\bigcirc\\) the solution will turn blue.
\\(\bigcirc\\) the solution will turn pink.
\\(\bigcirc\\) the solution will turn green.
- First, recall the properties of \( \ce{H2CO3} \): Carbonic acid (\( \ce{H2CO3} \)) is an acid, and in aqueous solution, it dissociates to produce \( \ce{H+} \) ions (\( \ce{H2CO3(aq)
ightleftharpoons H+(aq) + HCO3-(aq)} \), and further dissociation of \( \ce{HCO3-} \) also produces \( \ce{H+} \)).
- Now, look at the given equilibrium for bromothymol blue: \( \ce{HC2H3O2(aq)
ightleftharpoons H+(aq) + C2H3O2-(aq)} \) (yellow form on the left, blue form on the right).
- According to Le Chatelier's principle, when we add a large amount of \( \ce{H2CO3} \), the concentration of \( \ce{H+} \) ions in the solution increases significantly.
- An increase in \( \ce{[H+]} \) will shift the equilibrium of the bromothymol blue reaction to the left (because the system tries to counteract the increase in \( \ce{H+} \) by consuming it, so the reverse reaction is favored).
- Shifting the equilibrium to the left means more of the undissociated (yellow) form \( \ce{HC2H3O2} \) is present, so the solution will remain yellow (or become more yellow - dominated, but since it was likely in some equilibrium before, adding \( \ce{H+} \) pushes it left). The options of pink or green are not related to the given indicator's color change (bromothymol blue is yellow or blue, not pink/green), and turning blue would require the equilibrium to shift right (which would happen with a base, not an acid adding \( \ce{H+} \)).
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A. The solution will remain yellow.