Question

Bromothymol Blue is a liquid indicator that changes color from blue to green when carbon dioxide gas is mixed into the solution. When carbon dioxide leaves the solution, the color of the indicator changes from green to blue. Based on the information above, which of the following describes the kind of change present?

A. The color change shows this is a chemical change, because every time there is a color change this indicates a chemical change.

B. The color change shows this is a chemical change, because adding the gas caused the unexpected color change.

C. The color change shows this is a physical change, because blue and green are similar colors and the gas did not cause the change.

D. The color change shows this is a physical change, because the indicator only changed colors slightly.

Answer 1

The correct answer is option B, that is, the color change shows this is a chemical change because adding the gas caused the unexpected color change.

The bromothymol blue refers to a pH indicator that is used to determine the concentration of carbon dioxide in a solution. It changes its color to green in the existence of carbon dioxide gas. It is present in solid form and can be deprotonated or protonated that produces variations in color, that is, either green or yellow.  

The modification in the color of indicator suggests the chemical change as all this is taking place in the existence of carbon dioxide gas.