Mineral acids are measured by titration to a pH of 4.3 using which indicator?

Mineral acids are measured by titration to a pH of 4.3 using which indicator?

• A. 4.3, methyl red
• B. 8.3, methyl red
• C. 4.3, methyl orange
• D. 8.3, methyl orange

Answer: (B)

Think about where the titration should stop and which indicator changes color right at that pH. If you’re aiming for an endpoint around pH 4.3, you want an indicator whose color transition occurs in that acidic region. Methyl orange is the best fit because its color change happens roughly from pH 3.1 to 4.4, so it signals clearly right around 4.3. Methyl red, on the other hand, changes from about pH 4.4 to 6.2, which would indicate a later endpoint and could miss the cleaner endpoint near 4.3. So methyl orange provides the most accurate, noticeable endpoint at that pH.

Think about where the titration should stop and which indicator changes color right at that pH. If you’re aiming for an endpoint around pH 4.3, you want an indicator whose color transition occurs in that acidic region. Methyl orange is the best fit because its color change happens roughly from pH 3.1 to 4.4, so it signals clearly right around 4.3. Methyl red, on the other hand, changes from about pH 4.4 to 6.2, which would indicate a later endpoint and could miss the cleaner endpoint near 4.3. So methyl orange provides the most accurate, noticeable endpoint at that pH.