Final answer:
Blowing into a bromothymol blue water solution introduces carbon dioxide, leading to the formation of carbonic acid, which lowers the pH and changes the solution's color from blue to green and finally to yellow, depending on the amount of CO2 introduced.
Step-by-step explanation:
When you blow into a straw causing bromothymol blue water solution to bubble, you introduce carbon dioxide (CO2) into the solution. Bromothymol blue is a pH indicator that changes color depending on the acidity or alkalinity of the solution it is in. Normally, it is blue in neutral water, turning green in slightly acidic solutions, and yellow when the solution is more acidic.
By blowing into the water, you are exhaling CO2, which reacts with water to form carbonic acid (H2CO3). This acid will decrease the pH of the solution, making it more acidic and causing the bromothymol blue to change from blue to green and eventually to yellow if enough CO2 is bubbled through.
Why bromothymol blue was used
Bromothymol blue was used when mixing hydrochloric acid and sodium hydroxide because it can indicate the endpoint of the neutralization reaction taking place. The color change signifies whether the solution is acidic, neutral, or basic after the reaction.