Final answer:
Bromothymol blue is an acid-base indicator that changes color in the presence of carbon dioxide, which forms carbonic acid in water, lowering the pH. Other indicators, such as phenolphthalein and litmus, have different color change intervals and are suitable for different types of titrations.
Step-by-step explanation:
The liquid that changes color based on CO₂ levels is bromothymol blue. This substance is an acid-base indicator that can indicate the presence of carbon dioxide by changing color. When CO₂ is dissolved in water, it forms carbonic acid, which lowers the pH of the solution. Bromothymol blue is yellow in acidic conditions and blue in basic conditions. For example, it is often used in experiments where exhaled breath, which contains CO₂, is bubbled through a solution containing the indicator, causing a color change.
Other indicators mentioned, such as phenolphthalein and litmus, also change color in the presence of acids or bases, but they have different color change intervals and are suitable for different types of titrations. Phenolphthalein turns pink in basic solutions and is colorless in acidic solutions, making it useful for titrations that reach a pH above 8.3. Meanwhile, litmus turns blue in basic solutions and red in acidic solutions, though its color change occurs over a broader pH range and is less precise than phenolphthalein for titrations.