Question

Consider the following chemical reaction of bromothymol blue indicator. It appears yellow in undissociated form and blue in its dissociated aqueous solution.

HC2H3O2(aq) mc012-1.jpg H+(aq) + C2H3O2–(aq)
yellow blue

What will be the color of the solution if a large amount of H2CO3 is added?
The solution will remain yellow.
The solution will turn blue.
The solution will turn pink.
The solution will turn green.

Answer 1

The solution will remain yellow.

Answer 2

Answer is: The solution will remain yellow.

Balanced chemical reaction: HC₂H₃O₂(aq) ⇄ H⁺(aq) + C₂H₃O₂⁻(aq).

Carbonic acid dissociation in water: H₂CO₃ ⇄ H⁺(aq) + HCO₃⁻(aq).

According to Le Chatelier's Principle the position of equilibrium moves to counteract the change.

The position of equilibrium will move so that the concentration of hydrogen cations (H⁺) decreases and than concetration of acid (HC₂H₃O₂) increases.