Question

Alizarin yellow is a pH indicator that transitions from red to yellow when the pH falls from a value of 11 to below 10. Why is phenol red a better pH indicator than alizarin yellow for detecting a change in pH of broth containing pathogenic bacteria such as E. coli

Answer 1

The correct answer is - acidic conditions wouldn't trigger a change in the color of Alizarin yellow.

Step-by-step explanation:

The growth of E. coli generally occurs at neutral pH, however, its growth is normal at acidic conditions as well. The change in the growth of E. coli is not able to detect by alizarin.

The phenol red turns yellow in the presence of an acid, and the change in pH in an alkaline environment can be detected by the red color of phenol red. Growth of E.coli will grow in pH of 10-12 . But, very slowly. The color change in alizarin is also apparent at pH 10.2 to 12 only.