[orangebanana]

A beaker contains a solution that when phenolphthalein is added it turns pink. The uncovered beaker is left out and slowly the solution turns colorless. Explain what has happened. What chemical reaction has taken place?

Thanks in advance for any help.


EDIT - I've come up with the idea that carbonic acid would be formed from CO2 dissolving in solution, but what might this reaction be called?

[Borek]

A beaker contains a solution that when phenolphthalein is added it turns pink.

What does it tell you about the initial composition of the solution?

EDIT - I've come up with the idea that carbonic acid would be formed from CO2 dissolving in solution

Yes.

but what might this reaction be called?

Answer my first question and look at what you have in the solution when CO₂ dissolves.