<h2><u>Full Question:</u></h2>
The pH indicator bromothymol blue is blue in an alkaline solution and yellow in an acidic solution. A slight increase in acidity, such as when CO2 gas is added, causes a solution with the indicator to change from blue to yellow.
A solution with the indicator would turn from blue to yellow when which combination of factors exists? Select the two correct answers.
A. A person blows air into the solution through a straw.
B. Algae in the solution are placed under a bright light.
C. Yeast cells and sugar are placed in the solution.
D. A water plant in the solution is placed on a sunny windowsill.
<h2><u>Answer</u>:</h2>
Option A and C are correct options.
<h3><u>Explanation</u>:</h3>
Bromothymol is just a very good indicator just like phenolphthalein or litmus. The colour changes of Bromothymol is yellow in acid and blue in basic solution. Bromothymol is quite sensitive with respect to pH changes. That's why a slight changes of pH in the solution makes it change its colour.
Solution of carbon dioxide in water has the acid carbonic acid in it. So as the blue Bromothymol is added to such solution it turns yellow.
So, when air is blown through straw, carbon dioxide concentration in water increase which leads to formation of more carbonic acid. This causes change in colour.
Similarly the action of yeast on sugar also releases carbon dioxide. So as blue Bromothymol is added to this solution, there's a color change.
