HOSA Dental Terminology Practice

What effect does acidity have on litmus paper?

1. Changes it to blue

2. Makes it turn yellow

3. Causes it to become colorless

4. Makes it red

The correct answer is: Makes it red

Litmus paper is a common pH indicator used to determine the acidity or alkalinity of a solution. When litmus paper, which is originally blue or red, is exposed to an acidic solution (with a pH less than 7), it undergoes a color change. Specifically, blue litmus paper turns red in the presence of acid. This color shift occurs because the chemical structure of the dye in the litmus paper interacts with the hydrogen ions present in acidic environments, resulting in this visible change. In this context, the other outcomes presented do not align with the behavior of litmus paper in acidic conditions. For example, blue litmus turning blue (which would suggest no change and thus neutrality or alkalinity) and colorless (which does not typically occur with litmus indicators) do not reflect the expected results. The transformation to red is a clear and reliable indicator of acidity, making it essential for various applications in chemistry and biology.