International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What color is methyl orange in acidic solutions?

1. Yellow

2. Blue

3. Red

4. Pink

The correct answer is: Red

Methyl orange is an acid-base indicator that changes color depending on the pH of the solution. In acidic environments, methyl orange exhibits a red color. This occurs because the compound primarily exists in its protonated form at lower pH levels, which absorbs light in a way that produces a red appearance. As the pH increases and the solution becomes more alkaline, methyl orange transitions to a yellow color. However, in highly acidic solutions, the distinct red coloration is evident, making it a useful indicator for determining acidity in various chemical applications.