Question

Which of the following liquids can be used to check pH?

• A. Phenolphthalein
• B. Bromothymol blue
• C. Both $A$ and $B$
• D. None of the above

Answer 1

The correct option is C Both $A$ and $B$

A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually. Hence, a pH indicator is a chemical detector for hydronium ions ($H_3{O}^{+}$) or hydrogen ions ($H^{+}$). Bromophenol blue is used as a pH indicator, a color marker, and a dye. As an acid-base indicator, its useful range lies between pH 3.0 and 4.6. It changes from yellow at pH 3.0 to blue at pH 4.6; this reaction is reversible. Phenolphthalein is often used as an indicator in acid-base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions.