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

Which of the following is the correct color change of methyl orange in alkaline solutions?

1. Red

2. Blue

3. Orange

4. Yellow

The correct answer is: Yellow

Methyl orange is a pH indicator that is commonly used in titrations and other chemical analyses. It exhibits a distinct color change depending on the pH of the solution. In acidic environments, methyl orange appears red, and as the pH increases, it transitions through orange before becoming yellow in alkaline (basic) solutions. In alkaline solutions, the pH is typically above 4.4, where methyl orange is fully deprotonated, resulting in a yellow color. This behavior makes methyl orange particularly useful for identifying the acidity or alkalinity of a solution. The yellow color in alkaline conditions indicates that the solution has moved past the transition range, confirming a basic environment.